Merge pull request #3083 from skylartaylor/linked-path-checks

Resolve remote links and document-supplied output names safely

ATTRIBUTION.toml

@@ -7,7 +7,7 @@ licence = "MIT OR Apache-2.0"
 licence_file = "LICENSE-MIT"
 kind = "translation"
 usage = "Greek UI strings, compiled in by crates/ui-egui/src/i18n/mod.rs"
-sha256 = "cefa955aa92790d6773cb1d1e15e19019b3165a00528d57d6617362e1d1988ab"
+sha256 = "a3234684d5318ce38213c79533d3eebb9c635497ba9e00fb9ca7ebe2fad9d73d"
 
 # ATTRIBUTION.toml: one entry per asset (AGENTS.md §1). The source of truth for provenance and licences.
 # ATTRIBUTION.md is generated from this file: `cargo xtask assets --write`. Checked by `cargo xtask assets` (part of `xtask ci`).
@@ -30,7 +30,7 @@ licence = "MIT OR Apache-2.0"
 licence_file = "LICENSE-MIT"
 kind = "translation"
 usage = "Simplified Chinese UI strings, compiled in by crates/ui-egui/src/i18n/mod.rs"
-sha256 = "dbfebf4e9b2e9ac31ecf72202c2098173e72ebfaf90e9fee8f0563a6734fe31f"
+sha256 = "c5e0206846b009bcb366d092c3d64fd8b9e42d29d5406fb73ae36ecb1f2083d5"
 
 [[asset]]
 path = "crates/ui-egui/src/i18n/zh-hant.tsv"
@@ -41,7 +41,7 @@ licence = "MIT OR Apache-2.0"
 licence_file = "LICENSE-MIT"
 kind = "translation"
 usage = "Traditional Chinese UI strings, compiled in by crates/ui-egui/src/i18n/mod.rs"
-sha256 = "0b0dafa3806a6b3508684f64e1f07b435113f8efd0e59201d12250c63c1d9547"
+sha256 = "349a2ead371bdbfeefb9ab2279c676b205cefe163cbef174f8123fe4bf739ab9"
 
 [[asset]]
 path = "crates/ui-egui/src/i18n/cs.tsv"
@@ -52,7 +52,7 @@ licence = "MIT OR Apache-2.0"
 licence_file = "LICENSE-MIT"
 kind = "translation"
 usage = "Czech UI strings, compiled in by crates/ui-egui/src/i18n/mod.rs"
-sha256 = "898a5240fa59cac42ef6b99cb60bcfca0094ac27370e1c8d020bd27936b56517"
+sha256 = "cb332907792d4aa760ca9862160e24a7b469afdbcfb93235e99deb8d58604ae2"
 
 [[asset]]
 path = "crates/ui-egui/src/i18n/pt-br.tsv"
@@ -63,7 +63,7 @@ licence = "MIT OR Apache-2.0"
 licence_file = "LICENSE-MIT"
 kind = "translation"
 usage = "Brazilian Portuguese UI strings, compiled in by crates/ui-egui/src/i18n/mod.rs"
-sha256 = "b4745c94797575529cd0e78c18c71fa2c0dfddfbf19b9c40b41dc2057c6f6543"
+sha256 = "ebd3a12e471ba9d9a69e6532fbac2d027dec3c91b79cdfbb1c6c386d13de3bd6"
 
 [[asset]]
 path = "crates/ui-egui/src/i18n/es.tsv"
@@ -74,7 +74,7 @@ licence = "MIT OR Apache-2.0"
 licence_file = "LICENSE-MIT"
 kind = "translation"
 usage = "Spanish UI strings, compiled in by crates/ui-egui/src/i18n/mod.rs"
-sha256 = "2acb3f6522d6d1f744343f474fe4c51ebec610a888a7fa83fc9422228e6fa3c1"
+sha256 = "f5e0553165ab0223bfbc809b1630170d1af11d6546ae5a682d4090104b6e4a05"
 
 [[asset]]
 path = "crates/ui-egui/src/i18n/fr.tsv"
@@ -85,7 +85,7 @@ licence = "MIT OR Apache-2.0"
 licence_file = "LICENSE-MIT"
 kind = "translation"
 usage = "French UI strings, compiled in by crates/ui-egui/src/i18n/mod.rs"
-sha256 = "1b739478a4f186a49900cce84edbe136206a53b46340322df4caf77bb3fb5b12"
+sha256 = "dd2171a0a940a84e512fd6408a11cddf104be897ec4ab670c5ef6f1781ccb671"
 
 [[asset]]
 path = "crates/ui-egui/src/i18n/de.tsv"
@@ -96,7 +96,7 @@ licence = "MIT OR Apache-2.0"
 licence_file = "LICENSE-MIT"
 kind = "translation"
 usage = "German UI strings, compiled in by crates/ui-egui/src/i18n/mod.rs"
-sha256 = "da3b71608ff7fe6e230b076207cee96ac01f66e068ca1be83af1ad56ac9c60eb"
+sha256 = "1b9b3d0d6dab626c3acb8c9aa64d64e56b98eb3f2faf71dcb1957067e72706db"
 
 [[asset]]
 path = "crates/ui-egui/src/i18n/te.tsv"
@@ -107,7 +107,7 @@ licence = "MIT OR Apache-2.0"
 licence_file = "LICENSE-MIT"
 kind = "translation"
 usage = "Telugu UI strings, compiled in by crates/ui-egui/src/i18n/mod.rs"
-sha256 = "989d2e5f57cf22c21a85951835ca9fbd05e314da67eb4c17332df1f03679fa00"
+sha256 = "668f23f4095120343e3f0910dc8f5844765370fae40400c48d685cad20dcf60e"
 
 [[asset]]
 path = "crates/ui-egui/src/i18n/it.tsv"
@@ -118,7 +118,7 @@ licence = "MIT OR Apache-2.0"
 licence_file = "LICENSE-MIT"
 kind = "translation"
 usage = "Italian UI strings, compiled in by crates/ui-egui/src/i18n/mod.rs"
-sha256 = "5e84916e3ad8670216360695689fe8fd624365a29886f66a3c655ba126892f5b"
+sha256 = "02f3fd4b2721b0ea9c01c99d477a0339a28180514568179d3fc420e7fb81c671"
 
 [[asset]]
 path = "crates/ui-egui/src/i18n/pl.tsv"
@@ -129,7 +129,7 @@ licence = "MIT OR Apache-2.0"
 licence_file = "LICENSE-MIT"
 kind = "translation"
 usage = "Polish UI strings, compiled in by crates/ui-egui/src/i18n/mod.rs"
-sha256 = "988bcf2e0322a46c0464ff7b91ab5d90193b0ea7f454812d12595eb843de6fc7"
+sha256 = "26eb438c309d34e55eba959a21f139db91fa5fd1d6d4b7c3d1cd0fa79a60a5b0"
 
 [[asset]]
 path = "crates/ui-egui/src/i18n/ru.tsv"
@@ -140,7 +140,7 @@ licence = "MIT OR Apache-2.0"
 licence_file = "LICENSE-MIT"
 kind = "translation"
 usage = "Russian UI strings, compiled in by crates/ui-egui/src/i18n/mod.rs"
-sha256 = "084f4ea06f31c632ad90b0e87f66240ce5b5dc012ac7770987d44918ee66f452"
+sha256 = "c04b6d0320bce999b33bd189bffcec8a196d4169e56cc65675dc920c5a671dac"
 
 [[asset]]
 path = "crates/ui-egui/src/i18n/hu.tsv"
@@ -151,7 +151,7 @@ licence = "MIT OR Apache-2.0"
 licence_file = "LICENSE-MIT"
 kind = "translation"
 usage = "Hungarian UI strings, compiled in by crates/ui-egui/src/i18n/mod.rs"
-sha256 = "973cd90ec34c8a973d146a0e2c73c1d632e17357c3d87ccf10c59e64d12c1587"
+sha256 = "37b042977d934b0b550e5f52faa5d90abbcb9e7ff61ff9588021610ce709e474"
 
 [[asset]]
 path = "crates/ui-egui/src/i18n/bg.tsv"
@@ -162,7 +162,7 @@ licence = "MIT OR Apache-2.0"
 licence_file = "LICENSE-MIT"
 kind = "translation"
 usage = "Bulgarian UI strings, compiled in by crates/ui-egui/src/i18n/mod.rs"
-sha256 = "485f85d4053c9661ddda2ed9394a0644c77b489feb598d02f12ef209e11f2ee3"
+sha256 = "3d1f1d2558eec1271fa653bc38616feeefc6559deeb2a0cdbf07d67634e9ac97"
 
 [[asset]]
 path = "crates/ui-egui/src/i18n/kk.tsv"
@@ -173,7 +173,7 @@ licence = "MIT OR Apache-2.0"
 licence_file = "LICENSE-MIT"
 kind = "translation"
 usage = "Kazakh UI strings, compiled in by crates/ui-egui/src/i18n/mod.rs"
-sha256 = "24524864022ab2abeff68b5979519eee4e92134d0c4053d40c741bc7f01c249c"
+sha256 = "03071249bd6c13f79da72262415e484fb1aa36098a37a49094b9dab58cebc4e2"
 
 [[asset]]
 path = "crates/ui-egui/src/i18n/ja.tsv"
@@ -184,7 +184,7 @@ licence = "MIT OR Apache-2.0"
 licence_file = "LICENSE-MIT"
 kind = "translation"
 usage = "Japanese UI strings, compiled in by crates/ui-egui/src/i18n/mod.rs"
-sha256 = "bc6d123bdb34d5d7c22717fed1a86ff20e7e493acc1e155e61e61e2dc74459aa"
+sha256 = "c0ba73b27b95b275f5eebc040ab1c3c6c3b227c63e1c637b4cdb27d0a9264a8b"
 
 [[asset]]
 path = "crates/ui-egui/src/i18n/uk.tsv"
@@ -195,7 +195,7 @@ licence = "MIT OR Apache-2.0"
 licence_file = "LICENSE-MIT"
 kind = "translation"
 usage = "Ukrainian UI strings, compiled in by crates/ui-egui/src/i18n/mod.rs"
-sha256 = "82678dbe730f56062037ea78de165b2c016b3fa670fb1cbfc7cd713eca900bac"
+sha256 = "e3af76714ee9899328a453ec83195f4dc462fe48ba445fbe3688c777e74bc9dc"
 
 [[asset]]
 path = "crates/ui-egui/src/i18n/ar.tsv"
@@ -206,7 +206,7 @@ licence = "MIT OR Apache-2.0"
 licence_file = "LICENSE-MIT"
 kind = "translation"
 usage = "Arabic UI strings, compiled in by crates/ui-egui/src/i18n/mod.rs"
-sha256 = "304d661b27cdb5246f6b2974b4b5e78667f0928cda3588440be3d8f35f254679"
+sha256 = "0855d7f785c433799da83400ebc932f987eb543008486bc4f553aadb4102c2ba"
 
 [[asset]]
 path = "crates/ui-egui/src/i18n/tr.tsv"
@@ -217,7 +217,7 @@ licence = "MIT OR Apache-2.0"
 licence_file = "LICENSE-MIT"
 kind = "translation"
 usage = "Turkish UI strings, compiled in by crates/ui-egui/src/i18n/mod.rs"
-sha256 = "05e2b7d5401166d362ba055120fba9a1645d6ec324997cf670e19fafcb0c54cf"
+sha256 = "884ab18d60db52f65cd0e30530e196c73c0e627f450bc948517e2f4b7deeb04b"
 
 [[asset]]
 path = "crates/ui-egui/src/i18n/lt.tsv"
@@ -228,7 +228,7 @@ licence = "MIT OR Apache-2.0"
 licence_file = "LICENSE-MIT"
 kind = "translation"
 usage = "Lithuanian UI strings, compiled in by crates/ui-egui/src/i18n/mod.rs"
-sha256 = "17c8579e0e9d1524ffbeb87e7b30c14562dbaac64400826ee786cecfe31648fa"
+sha256 = "c805a2c6da08e77a9a7455856d82c168cf6f353d96e1dc140fcc8898f12ba538"
 
 
 [[asset]]
@@ -3352,7 +3352,7 @@ licence = "MIT OR Apache-2.0"
 licence_file = "LICENSE-MIT"
 kind = "translation"
 usage = "Vietnamese UI strings, compiled in by crates/ui-egui/src/i18n/mod.rs"
-sha256 = "2d1c4b4276d02512a4e20101be95a1671de5c4f5cdfd661887af5ebab0db06a6"
+sha256 = "11619064ae9edaeee5d601b7008e40095a40375a3e1a298155d59cb758fe7d34"
 
 [[asset]]
 path = "crates/ui-egui/src/i18n/sl.tsv"
@@ -3363,7 +3363,7 @@ licence = "MIT OR Apache-2.0"
 licence_file = "LICENSE-MIT"
 kind = "translation"
 usage = "Slovene UI strings, compiled in by crates/ui-egui/src/i18n/mod.rs"
-sha256 = "8f8a259264cda06eb6d9a9bf91dc7d873a8561213a9a9e7acbd32623bef40be0"
+sha256 = "89f2c7495cfb0fc9d36d35b95c056dbeda18ccae521250babac719ff5df62d89"
 
 [[asset]]
 

Cargo.lock

@@ -1142,6 +1142,11 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "craft-docpath"
+version = "0.1.0"
+source = "git+https://github.com/storytold/craft-libs?rev=82a24b006eefa036b43c09a67fb9a3fbd17ffe63#82a24b006eefa036b43c09a67fb9a3fbd17ffe63"
+
 [[package]]
 name = "craft-print"
 version = "0.1.0"
@@ -4100,6 +4105,7 @@ name = "pdfcraft-engine"
 version = "0.8.0"
 dependencies = [
  "chrono",
+ "craft-docpath",
  "icu_properties",
  "idna",
  "image",

Cargo.toml

@@ -18,6 +18,8 @@ craft-ui = { git = "https://github.com/storytold/craft-libs", version = "0.1.0",
 craft-quit = { git = "https://github.com/storytold/craft-libs", version = "0.1.0", rev = "f58bc1a3df490992d633393d0898af0588ce882c" }
 # Shared system spooler; document composition remains in pdfcraft-print.
 craft-print = { git = "https://github.com/storytold/craft-libs", version = "0.1.0", rev = "666c358065261a2816b376fa3bb10538dbf53040" }
+# Whether a path stored in a document may be opened (GoToR link targets).
+craft-docpath = { version = "0.1.0", git = "https://github.com/storytold/craft-libs", rev = "82a24b006eefa036b43c09a67fb9a3fbd17ffe63" }
 # internal
 pdfcraft-geom = { path = "crates/geom", version = "0.8.0" }
 pdfcraft-filters = { path = "crates/filters", version = "0.8.0" }

apps/pdfcraft/src/main.rs

@@ -231,7 +231,10 @@ fn main() -> eframe::Result {
     // running and exits (#282, #317, #1726). Any option means the caller wants this launch's own
     // window.
     let may_hand_off = !new_window && !files.is_empty() && options.is_empty() && control_file.is_none() && !create_images;
-    let instance = match single_instance::claim(&single_instance::absolute(&files), may_hand_off) {
+    // Absolute for this instance too: links relative to a document resolve against its folder,
+    // never the working directory.
+    let files = single_instance::absolute(&files);
+    let instance = match single_instance::claim(&files, may_hand_off) {
         single_instance::Claim::HandedOff => return Ok(()),
         single_instance::Claim::Primary(server) => Some(server),
         single_instance::Claim::Alone => None,

crates/engine/Cargo.toml

@@ -9,6 +9,7 @@ license.workspace = true
 workspace = true
 
 [dependencies]
+craft-docpath = { workspace = true }
 pdfcraft-measure = { workspace = true }
 image = { version = "0.25", default-features = false, features = ["png", "jpeg", "tiff"] }
 pdfcraft-render = { workspace = true }

crates/engine/src/links.rs

@@ -137,7 +137,8 @@ pub enum RemoteDocumentPathError {
     Empty,
     TooLong,
     Hidden,
-    UrlOrNetwork,
+    /// A URL, a network or device path, or a path that climbs above its root.
+    NotLocal(craft_docpath::Refused),
     MissingSourcePath,
     /// The target doesn't end in `.pdf`.
     NotPdf,
@@ -155,7 +156,7 @@ impl std::fmt::Display for RemoteDocumentPathError {
             Self::Empty => f.write_str("the file specification is empty"),
             Self::TooLong => f.write_str("the file specification is too long"),
             Self::Hidden => f.write_str("the file specification contains hidden or control characters"),
-            Self::UrlOrNetwork => f.write_str("only local document paths are supported"),
+            Self::NotLocal(r) => write!(f, "only local document paths are supported: {r}"),
             Self::MissingSourcePath => f.write_str("a relative link needs a source document path"),
             Self::NotPdf => f.write_str("the linked file is not a .pdf file"),
             Self::NotAFile => f.write_str("the linked path is not a regular file"),
@@ -173,7 +174,9 @@ pub fn remote_document_path_is_absolute(raw: &str) -> bool {
 }
 
 /// Resolve a PDF remote-Go-To file specification to a local path without opening it.
-/// Relative paths are based on the source document; an in-memory source has no fallback to CWD.
+/// Relative paths are based on the source document, which should be an absolute path; an
+/// in-memory source has no fallback to CWD. URLs (including `file:`), network and device paths are
+/// refused ([`craft_docpath::resolve`]).
 pub fn resolve_remote_document_path(source: Option<&Path>, raw: &str) -> Result<PathBuf, RemoteDocumentPathError> {
     if raw.is_empty() || raw.trim().is_empty() {
         return Err(RemoteDocumentPathError::Empty);
@@ -184,25 +187,22 @@ pub fn resolve_remote_document_path(source: Option<&Path>, raw: &str) -> Result<
     if raw.chars().any(hides_text) {
         return Err(RemoteDocumentPathError::Hidden);
     }
-    if raw.starts_with("//") || raw.starts_with("\\\\") || raw.starts_with("/\\") || raw.starts_with("\\/") {
+    // A GoToR file specification is a path, not a URL: any scheme of two or more characters is
-        return Err(RemoteDocumentPathError::UrlOrNetwork);
+    // refused (one letter is a drive), `file:` and names such as `custom:target.pdf` included.
-    }
-    let path = Path::new(raw);
-    let drive_absolute = remote_document_path_is_absolute(raw);
     if let Some((scheme, _)) = raw.split_once(':') {
-        let valid_scheme = scheme.chars().next().is_some_and(|c| c.is_ascii_alphabetic())
+        let is_scheme = scheme.len() > 1
+            && scheme.chars().next().is_some_and(|c| c.is_ascii_alphabetic())
             && scheme.chars().all(|c| c.is_ascii_alphanumeric() || matches!(c, '+' | '-' | '.'));
-        let windows_drive = scheme.len() == 1 && drive_absolute;
+        if is_scheme {
-        if valid_scheme && !windows_drive {
+            return Err(RemoteDocumentPathError::NotLocal(craft_docpath::Refused::Url));
-            return Err(RemoteDocumentPathError::UrlOrNetwork);
         }
     }
-    if drive_absolute {
+    let path = craft_docpath::resolve(raw, source).map_err(RemoteDocumentPathError::NotLocal)?;
-        return Ok(path.to_path_buf());
+    // A relative result would be read against the working directory.
+    if !path.is_absolute() {
+        return Err(RemoteDocumentPathError::MissingSourcePath);
     }
-    let source = source.ok_or(RemoteDocumentPathError::MissingSourcePath)?;
+    Ok(path)
-    let parent = source.parent().ok_or(RemoteDocumentPathError::MissingSourcePath)?;
-    Ok(parent.join(path))
 }
 
 /// Largest linked PDF a GoToR link may open (1 GiB, the largest size the large-file work measures).
@@ -503,23 +503,56 @@ mod tests {
         use super::{RemoteDocumentPathError as E, resolve_remote_document_path as resolve};
         use std::path::Path;
 
-        let source = Path::new("/docs/chapter/source.pdf");
+        let source = std::env::temp_dir().join("chapter").join("source.pdf");
-        assert_eq!(resolve(Some(source), "../target.pdf").as_deref(), Ok(Path::new("/docs/chapter/../target.pdf")));
+        let source = source.as_path();
+        let folder = source.parent().unwrap();
+        assert_eq!(resolve(Some(source), "target.pdf"), Ok(folder.join("target.pdf")));
+        assert_eq!(resolve(Some(source), "../target.pdf").as_deref(), Ok(folder.parent().unwrap().join("target.pdf").as_path()));
+        #[cfg(unix)]
         assert_eq!(resolve(Some(source), "/manual/target.pdf").as_deref(), Ok(Path::new("/manual/target.pdf")));
         assert_eq!(resolve(None, "target.pdf"), Err(E::MissingSourcePath));
+        assert_eq!(resolve(Some(Path::new("source.pdf")), "target.pdf"), Err(E::MissingSourcePath), "a relative source is not used");
         assert_eq!(resolve(Some(source), ""), Err(E::Empty));
         assert_eq!(resolve(Some(source), "   "), Err(E::Empty));
-        for url in ["file:///tmp/a.pdf", "https://example.org/a.pdf", "smb://host/share/a.pdf", "ftp://host/a.pdf", "custom:target.pdf"] {
+        for url in
-            assert_eq!(resolve(Some(source), url), Err(E::UrlOrNetwork), "{url}");
+            ["file:///tmp/a.pdf", "file://h/s/a.pdf", "https://example.org/a.pdf", "smb://host/share/a.pdf", "ftp://host/a.pdf", "custom:target.pdf"]
-        }
-        for network_path in ["//server/share/a.pdf", "\\\\server\\share\\a.pdf", "\\\\?\\C:\\a.pdf", "\\\\.\\device\\a.pdf", "/\\server/share/a.pdf"]
         {
-            assert_eq!(resolve(Some(source), network_path), Err(E::UrlOrNetwork), "{network_path:?}");
+            assert!(matches!(resolve(Some(source), url), Err(E::NotLocal(_))), "{url}");
         }
         assert_eq!(resolve(Some(source), "folder/hidden\u{200B}.pdf"), Err(E::Hidden));
         assert_eq!(resolve(Some(source), &"a".repeat(super::MAX_REMOTE_DOCUMENT_PATH_BYTES + 1)), Err(E::TooLong));
     }
 
+    #[test]
+    fn remote_document_paths_to_other_computers_and_devices_are_refused() {
+        use super::{RemoteDocumentPathError as E, resolve_remote_document_path as resolve};
+
+        let source = std::env::temp_dir().join("chapter").join("source.pdf");
+        let source = source.as_path();
+        // Refused before any filesystem access: none of these exist, and a stat of a network path
+        // would contact its host.
+        for not_local in [
+            "//server/share/a.pdf",
+            "\\\\server\\share\\a.pdf",
+            "\\\\h\\s\\a.pdf",
+            "\\\\?\\UNC\\h\\s\\a.pdf",
+            "\\??\\UNC\\h\\s\\a.pdf",
+            "/??/x",
+            "\\??\\C:\\a.pdf",
+            "\\\\.\\device\\a.pdf",
+            "/\\server/share/a.pdf",
+            "NUL.pdf",
+        ] {
+            assert!(matches!(resolve(Some(source), not_local), Err(E::NotLocal(_))), "{not_local:?}");
+        }
+        // Linux reads `//tmp/x` as `/tmp/x`, but on Windows it names a share.
+        #[cfg(unix)]
+        {
+            let doubled = format!("/{}", source.with_file_name("a.pdf").display());
+            assert!(matches!(resolve(Some(source), &doubled), Err(E::NotLocal(_))), "{doubled}");
+        }
+    }
+
     #[test]
     fn urls_follow_the_artcraft_scheme() {
         assert_eq!(super::APP_PAGE, format!("{}/apps/{}", super::WEBSITE, super::APP));

crates/ui-egui/src/dialogs.rs

@@ -738,8 +738,7 @@ fn dialogs(app: &mut PdfCraftApp, ctx: &egui::Context) {
                 match action {
                     Some(crate::sign_ui::CertAction::Trust(c)) => app.trust_certificate(*c),
                     Some(crate::sign_ui::CertAction::Export(c)) => {
-                        let pem = crate::sign_ui::certificate_pem(&c);
+                        app.export_certificate(&c);
-                        app.write_files(&[(format!("{}.cer", c.display_name()), std::sync::Arc::new(pem.into_bytes()))], "Export certificate");
                     }
                     None => {}
                 }

crates/ui-egui/src/files.rs

@@ -195,9 +195,9 @@ pub(crate) fn file_stem_from_user(name: &str) -> String {
     if reserved { format!("_{stem}") } else { stem.to_string() }
 }
 
-/// A safe native Save suggestion for a PDF-supplied attachment name.
+/// A plain file name for a PDF-supplied attachment name: the Save suggestion, and the tab name
-/// This changes only the suggestion, never the stored name or the selected destination.
+/// (which later names files written from that tab). It never changes the stored name or a
-#[cfg(any(test, not(target_arch = "wasm32")))]
+/// destination the user selected.
 pub(crate) fn attachment_file_name(name: &str) -> String {
     let cleaned: String = name
         .chars()
@@ -217,6 +217,14 @@ pub(crate) fn attachment_file_name(name: &str) -> String {
     if reserved { format!("_{name}") } else { name.to_string() }
 }
 
+/// Whether `name` names a file directly inside a folder: not empty, `.` or `..`, with no `/` or
+/// `\\`, and no drive (`C:`). On Windows any `:` is refused, which also rules out alternate data
+/// streams.
+pub(crate) fn is_plain_file_name(name: &str) -> bool {
+    let drive = matches!(name.as_bytes(), [letter, b':', ..] if letter.is_ascii_alphabetic());
+    !(name.is_empty() || name == "." || name == ".." || name.contains(['/', '\\']) || drive || (cfg!(windows) && name.contains(':')))
+}
+
 /// Pages ▸ Rotate Pages.
 #[derive(Clone, Debug, PartialEq)]
 pub struct RotateDraft {
@@ -667,7 +675,12 @@ impl PdfCraftApp {
 
     /// [`Self::write_files`], then `after` once every file is written: now, or on a later frame
     /// when the user chooses the folder. `after` never runs when writing fails or is cancelled.
+    /// Every name must be a plain file name ([`is_plain_file_name`]); otherwise nothing is written.
     pub(crate) fn write_files_then(&mut self, named: Vec<(String, Arc<Vec<u8>>)>, title: &str, after: impl FnOnce(&mut Self) + Send + 'static) {
+        if let Some((name, _)) = named.iter().find(|(name, _)| !is_plain_file_name(name)) {
+            self.notify_fmt("Couldn't write {name}: {e}", &[("name", name), ("e", tl!("the name is not a plain file name"))]);
+            return;
+        }
         #[cfg(not(target_arch = "wasm32"))]
         {
             let write = move |app: &mut Self, dir: std::path::PathBuf| {
@@ -996,7 +1009,7 @@ impl PdfCraftApp {
 
 #[cfg(test)]
 mod stem_tests {
-    use super::{attachment_file_name, file_stem_from_user};
+    use super::{attachment_file_name, file_stem_from_user, is_plain_file_name};
 
     #[test]
     fn user_file_names_stay_inside_the_folder_and_writable_everywhere() {
@@ -1049,4 +1062,36 @@ mod stem_tests {
             assert_eq!(attachment_file_name(&once), once);
         }
     }
+
+    #[test]
+    fn write_files_refuses_names_that_leave_the_folder() {
+        let dir = std::env::temp_dir().join(format!("pdfcraft-write-files-{}", std::process::id()));
+        let _ = std::fs::remove_dir_all(&dir);
+        let out = dir.join("a").join("out");
+        std::fs::create_dir_all(&out).unwrap();
+        let absolute = dir.join("abs.pdf").to_string_lossy().into_owned();
+        let mut app = crate::PdfCraftApp::new();
+        app.set_option("language", "en").unwrap();
+        app.export_dir_override = Some(out.to_string_lossy().into_owned());
+        for bad in ["../x.pdf", "..", ".", "", "sub/x.pdf", "sub\\x.pdf", "C:x.pdf", absolute.as_str()] {
+            assert!(!is_plain_file_name(bad), "{bad}");
+            // A plain name first: nothing is written when any name in the batch is refused.
+            app.write_files(&[("ok.pdf".into(), std::sync::Arc::new(b"%PDF".to_vec())), (bad.into(), std::sync::Arc::new(b"%PDF".to_vec()))], "t");
+            assert!(app.toast.as_ref().is_some_and(|t| t.0.contains("not a plain file name")), "{bad}");
+        }
+        let names: Vec<_> = walk(&dir);
+        assert!(names.is_empty(), "{names:?}");
+        app.write_files(&[("x.pdf".into(), std::sync::Arc::new(b"%PDF".to_vec()))], "t");
+        assert_eq!(walk(&dir), vec![out.join("x.pdf")]);
+        let _ = std::fs::remove_dir_all(&dir);
+    }
+
+    fn walk(dir: &std::path::Path) -> Vec<std::path::PathBuf> {
+        let mut out = Vec::new();
+        for entry in std::fs::read_dir(dir).unwrap() {
+            let path = entry.unwrap().path();
+            if path.is_dir() { out.extend(walk(&path)) } else { out.push(path) }
+        }
+        out
+    }
 }

crates/ui-egui/src/i18n/ar.tsv

@@ -1703,6 +1703,7 @@
 	Couldn't use {name}: {e}	تعذّر استخدام {name}: {e}
 	Couldn't extract pages: {e}	تعذّر استخراج الصفحات: {e}
 	Couldn't write {name}: {e}	تعذّرت كتابة {name}: {e}
+	the name is not a plain file name	الاسم ليس اسم ملف بسيطًا
 	Wrote 1 file to {dir}	كُتب ملف واحد في {dir}
 	Wrote {n} files to {dir}	كُتب {n} ملفات في {dir}
 	No pages match those choices	لا صفحات تطابق هذه الاختيارات

crates/ui-egui/src/i18n/bg.tsv

@@ -1664,6 +1664,7 @@
 	Couldn't use {name}: {e}	{name} не можа да бъде използван: {e}
 	Couldn't extract pages: {e}	Страниците не можаха да бъдат извлечени: {e}
 	Couldn't write {name}: {e}	{name} не можа да бъде записан: {e}
+	the name is not a plain file name	името не е обикновено име на файл
 	Wrote 1 file to {dir}	Записан е 1 файл в {dir}
 	Wrote {n} files to {dir}	Записани са {n} файла в {dir}
 	No pages match those choices	Няма страници, отговарящи на този избор

crates/ui-egui/src/i18n/cs.tsv

@@ -1755,6 +1755,7 @@ key	Space	Mezerník
 	Couldn't use {name}: {e}	{name} nelze použít: {e}
 	Couldn't extract pages: {e}	Stránky nelze extrahovat: {e}
 	Couldn't write {name}: {e}	{name} nelze zapsat: {e}
+	the name is not a plain file name	název není prostý název souboru
 	Wrote 1 file to {dir}	Zapsán 1 soubor do {dir}
 	Wrote {n} files to {dir}	Zapsáno souborů: {n} (složka {dir})
 	No pages match those choices	Těmto volbám neodpovídají žádné stránky

crates/ui-egui/src/i18n/de.tsv

@@ -1637,6 +1637,7 @@
 	Couldn't use {name}: {e}	{name} konnte nicht verwendet werden: {e}
 	Couldn't extract pages: {e}	Seiten konnten nicht extrahiert werden: {e}
 	Couldn't write {name}: {e}	{name} konnte nicht geschrieben werden: {e}
+	the name is not a plain file name	der Name ist kein einfacher Dateiname
 	Wrote 1 file to {dir}	1 Datei nach {dir} geschrieben
 	Wrote {n} files to {dir}	{n} Dateien nach {dir} geschrieben
 	No pages match those choices	Keine Seiten entsprechen dieser Auswahl

crates/ui-egui/src/i18n/el.tsv

@@ -1215,6 +1215,7 @@
 	Couldn't use {name}: {e}	Δεν ήταν δυνατή η χρήση του {name}: {e}
 	Couldn't extract pages: {e}	Δεν ήταν δυνατή η εξαγωγή σελίδων: {e}
 	Couldn't write {name}: {e}	Δεν ήταν δυνατή η εγγραφή του {name}: {e}
+	the name is not a plain file name	το όνομα δεν είναι απλό όνομα αρχείου
 	Wrote 1 file to {dir}	Γράφτηκε 1 αρχείο στον φάκελο {dir}
 	Wrote {n} files to {dir}	Γράφτηκαν {n} αρχεία στον φάκελο {dir}
 	No pages match those choices	Καμία σελίδα δεν αντιστοιχεί σε αυτές τις επιλογές

crates/ui-egui/src/i18n/es.tsv

@@ -1714,6 +1714,7 @@ action wizard	Start	Iniciar
 	Couldn't use {name}: {e}	No se pudo usar {name}: {e}
 	Couldn't extract pages: {e}	No se pudieron extraer las páginas: {e}
 	Couldn't write {name}: {e}	No se pudo escribir {name}: {e}
+	the name is not a plain file name	el nombre no es un nombre de archivo simple
 	Wrote 1 file to {dir}	Se ha escrito 1 archivo en {dir}
 	Wrote {n} files to {dir}	Se han escrito {n} archivos en {dir}
 	No pages match those choices	Ninguna página coincide con esas opciones

crates/ui-egui/src/i18n/fr.tsv

@@ -1632,6 +1632,7 @@
 	Couldn't use {name}: {e}	Impossible d'utiliser {name} : {e}
 	Couldn't extract pages: {e}	Impossible d'extraire les pages : {e}
 	Couldn't write {name}: {e}	Impossible d'écrire {name} : {e}
+	the name is not a plain file name	le nom n'est pas un simple nom de fichier
 	Wrote 1 file to {dir}	1 fichier écrit dans {dir}
 	Wrote {n} files to {dir}	{n} fichiers écrits dans {dir}
 	No pages match those choices	Aucune page ne correspond à ces choix

crates/ui-egui/src/i18n/hu.tsv

@@ -1622,6 +1622,7 @@
 	Couldn't use {name}: {e}	{name} használata nem sikerült: {e}
 	Couldn't extract pages: {e}	Az oldalakat nem sikerült kinyerni: {e}
 	Couldn't write {name}: {e}	{name} írása nem sikerült: {e}
+	the name is not a plain file name	a név nem egyszerű fájlnév
 	Wrote 1 file to {dir}	1 fájl ide írva: {dir}
 	Wrote {n} files to {dir}	{n} fájl ide írva: {dir}
 	No pages match those choices	Egy oldal sem felel meg ezeknek a választásoknak

crates/ui-egui/src/i18n/it.tsv

@@ -1709,6 +1709,7 @@
 	Couldn't use {name}: {e}	Impossibile usare {name}: {e}
 	Couldn't extract pages: {e}	Impossibile estrarre le pagine: {e}
 	Couldn't write {name}: {e}	Impossibile scrivere {name}: {e}
+	the name is not a plain file name	il nome non è un semplice nome file
 	Wrote 1 file to {dir}	Scritto 1 file in {dir}
 	Wrote {n} files to {dir}	Scritti {n} file in {dir}
 	No pages match those choices	Nessuna pagina corrisponde a queste scelte

crates/ui-egui/src/i18n/ja.tsv

@@ -1713,6 +1713,7 @@
 	Couldn't use {name}: {e}	{name} を使用できませんでした: {e}
 	Couldn't extract pages: {e}	ページを抽出できませんでした: {e}
 	Couldn't write {name}: {e}	{name} に書き込めませんでした: {e}
+	the name is not a plain file name	名前が単独のファイル名ではありません
 	Wrote 1 file to {dir}	{dir} に 1 ファイルを書き込みました
 	Wrote {n} files to {dir}	{dir} に {n} ファイルを書き込みました
 	No pages match those choices	条件に一致するページはありません

crates/ui-egui/src/i18n/kk.tsv

@@ -1634,6 +1634,7 @@
 	Couldn't use {name}: {e}	{name} файлын пайдалану мүмкін болмады: {e}
 	Couldn't extract pages: {e}	Беттерді шығарып алу мүмкін болмады: {e}
 	Couldn't write {name}: {e}	{name} файлына жазу мүмкін болмады: {e}
+	the name is not a plain file name	атау қарапайым файл атауы емес
 	Wrote 1 file to {dir}	1 файл {dir} ішіне жазылды
 	Wrote {n} files to {dir}	{n} файл {dir} ішіне жазылды
 	No pages match those choices	Ешбір бет бұл таңдауларға сәйкес келмейді

crates/ui-egui/src/i18n/lt.tsv

@@ -1965,6 +1965,7 @@ comment menu	Edit	Redaguoti
 	Couldn't use the photo: {e}	Nepavyko panaudoti nuotraukos: {e}
 	Couldn't use {name}: {e}	Nepavyko panaudoti {name}: {e}
 	Couldn't write {name}: {e}	Nepavyko įrašyti {name}: {e}
+	the name is not a plain file name	vardas nėra paprastas failo vardas
 	Couldn't write {path}: {e}	Nepavyko įrašyti {path}: {e}
 	Create link	Kurti saitą
 	Created 1 link	Sukurtas 1 saitas

crates/ui-egui/src/i18n/pl.tsv

@@ -1696,6 +1696,7 @@
 	Couldn't use {name}: {e}	Nie można użyć {name}: {e}
 	Couldn't extract pages: {e}	Nie można wyodrębnić stron: {e}
 	Couldn't write {name}: {e}	Nie można zapisać {name}: {e}
+	the name is not a plain file name	nazwa nie jest zwykłą nazwą pliku
 	Wrote 1 file to {dir}	Zapisano 1 plik w {dir}
 	Wrote {n} files to {dir}	Liczba plików zapisanych w {dir}: {n}
 	No pages match those choices	Żadna strona nie pasuje do wybranych opcji

crates/ui-egui/src/i18n/pt-br.tsv

@@ -1538,6 +1538,7 @@
 	Couldn't use {name}: {e}	Não foi possível usar {name}: {e}
 	Couldn't extract pages: {e}	Não foi possível extrair páginas: {e}
 	Couldn't write {name}: {e}	Não foi possível gravar {name}: {e}
+	the name is not a plain file name	o nome não é um nome de arquivo simples
 	Wrote 1 file to {dir}	1 arquivo gravado em {dir}
 	Wrote {n} files to {dir}	{n} arquivos gravados em {dir}
 	No pages match those choices	Nenhuma página corresponde a essas opções

crates/ui-egui/src/i18n/ru.tsv

@@ -1704,6 +1704,7 @@
 	Couldn't use {name}: {e}	Не удалось использовать {name}: {e}
 	Couldn't extract pages: {e}	Не удалось извлечь страницы: {e}
 	Couldn't write {name}: {e}	Не удалось записать {name}: {e}
+	the name is not a plain file name	имя не является простым именем файла
 	Wrote 1 file to {dir}	Записан 1 файл в {dir}
 	Wrote {n} files to {dir}	Записано {n} файлов в {dir}
 	No pages match those choices	Страницы не соответствуют этим выбору

crates/ui-egui/src/i18n/sl.tsv

@@ -479,6 +479,7 @@
 	Couldn't take the snapshot: {e}	Posnetka ni bilo mogoče usvariti: {e}
 	Couldn't use {name}: {e}	Datoteke {name} ni bilo mogoče uporabiti: {e}
 	Couldn't write {name}: {e}	Datoteke {name} ni bilo mogoče zapisati: {e}
+	the name is not a plain file name	ime ni preprosto ime datoteke
 	Couldn't write {path}: {e}	Poti {path} ni bilo mogoče zapisati: {e}
 	Counterclockwise 90 degrees	90 stopinj v levo
 	Country/Region	Država/regija

crates/ui-egui/src/i18n/te.tsv

@@ -1623,6 +1623,7 @@ action wizard	Start	ప్రారంభించు
 	Couldn't use {name}: {e}	{name}ను ఉపయోగించడం సాధ్యం కాలేదు: {e}
 	Couldn't extract pages: {e}	పేజీలను వేరు తీయడం సాధ్యం కాలేదు: {e}
 	Couldn't write {name}: {e}	{name}ను రాయడం సాధ్యం కాలేదు: {e}
+	the name is not a plain file name	పేరు సాధారణ ఫైల్ పేరు కాదు
 	Wrote 1 file to {dir}	{dir}లో 1 ఫైల్ సేవ్ చేయబడింది
 	Wrote {n} files to {dir}	{dir}లో {n} ఫైల్‌లు సేవ్ చేయబడ్డాయి
 	No pages match those choices	ఆ ఎంపికలకు సరిపోయే పేజీలు ఏవీ లేవు

crates/ui-egui/src/i18n/tr.tsv

@@ -1603,6 +1603,7 @@
 	Couldn't use {name}: {e}	{name} kullanılamadı: {e}
 	Couldn't extract pages: {e}	Sayfalar ayıklanamadı: {e}
 	Couldn't write {name}: {e}	{name} yazılamadı: {e}
+	the name is not a plain file name	ad, basit bir dosya adı değil
 	Wrote 1 file to {dir}	1 dosya {dir} konumuna yazıldı
 	Wrote {n} files to {dir}	{n} dosya {dir} konumuna yazıldı
 	No pages match those choices	Bu seçimlerle eşleşen sayfa yok

crates/ui-egui/src/i18n/uk.tsv

@@ -1701,6 +1701,7 @@
 	Couldn't use {name}: {e}	Не вдалося використати {name}: {e}
 	Couldn't extract pages: {e}	Не вдалося видобути сторінки: {e}
 	Couldn't write {name}: {e}	Не вдалося записати {name}: {e}
+	the name is not a plain file name	назва не є простою назвою файлу
 	Wrote 1 file to {dir}	Записано 1 файл у {dir}
 	Wrote {n} files to {dir}	Записано файлів ({n}) у {dir}
 	No pages match those choices	Жодна сторінка не відповідає вибраним параметрам

crates/ui-egui/src/i18n/vi.tsv

@@ -1955,6 +1955,7 @@ comment menu	Edit	Sửa
 	Couldn't use the photo: {e}	Không thể dùng ảnh: {e}
 	Couldn't use {name}: {e}	Không thể dùng {name}: {e}
 	Couldn't write {name}: {e}	Không thể ghi {name}: {e}
+	the name is not a plain file name	tên không phải là tên tệp đơn thuần
 	Couldn't write {path}: {e}	Không thể ghi {path}: {e}
 	Create link	Tạo liên kết
 	Created 1 link	Đã tạo 1 liên kết

crates/ui-egui/src/i18n/zh-hans.tsv

@@ -1671,6 +1671,7 @@
 	Couldn't use {name}: {e}	无法使用{name}：{e}
 	Couldn't extract pages: {e}	无法提取页面：{e}
 	Couldn't write {name}: {e}	无法写入{name}：{e}
+	the name is not a plain file name	名称不是单纯的文件名
 	Wrote 1 file to {dir}	已将 1 个文件写入{dir}
 	Wrote {n} files to {dir}	已将{n}个文件写入{dir}
 	No pages match those choices	所选条件没有匹配的页面

crates/ui-egui/src/i18n/zh-hant.tsv

@@ -1615,6 +1615,7 @@
 	Couldn't use {name}: {e}	無法使用{name}：{e}
 	Couldn't extract pages: {e}	無法提取頁面：{e}
 	Couldn't write {name}: {e}	無法寫入{name}：{e}
+	the name is not a plain file name	名稱不是單純的檔案名稱
 	Wrote 1 file to {dir}	已將 1 個檔案寫入{dir}
 	Wrote {n} files to {dir}	已將{n}個檔案寫入{dir}
 	No pages match those choices	所選條件沒有匹配的頁面

crates/ui-egui/src/lib.rs

@@ -1520,7 +1520,8 @@ impl PdfCraftApp {
         match (data, open) {
             (Err(e), _) => self.notify_fmt("Couldn't read {name}: {e}", &[("name", &att.name), ("e", &e.to_string())]),
             (Ok(bytes), true) => {
-                if let Err(e) = self.open_bytes(&att.name, None, bytes) {
+                // The tab name later names files written from the tab (Split, Extract pages).
+                if let Err(e) = self.open_bytes(&crate::files::attachment_file_name(&att.name), None, bytes) {
                     self.notify_fmt("Couldn't open {name}: {e}", &[("name", &att.name), ("e", &e.to_string())]);
                 }
             }

crates/ui-egui/src/panels.rs

@@ -784,8 +784,7 @@ pub fn right_panel(app: &mut PdfCraftApp, ui: &mut egui::Ui) {
             app.start_signing(page, None, Some(field), None);
         }
         Some(crate::sign_ui::PanelAction::ExportCertificate(c)) => {
-            let pem = crate::sign_ui::certificate_pem(&c);
+            app.export_certificate(&c);
-            app.write_files(&[(format!("{}.cer", c.display_name()), std::sync::Arc::new(pem.into_bytes()))], "Export certificate");
         }
         None => {}
     }

crates/ui-egui/src/sign_ui.rs

@@ -266,6 +266,12 @@ fn entry_unusable(u: &sign::windows::Unusable) -> DigitalIdEntry {
 }
 
 impl PdfCraftApp {
+    /// Export certificate: write `c` as PEM into a chosen folder, named after its subject.
+    pub(crate) fn export_certificate(&mut self, c: &Certificate) {
+        let name = format!("{}.cer", crate::files::attachment_file_name(&c.display_name()));
+        self.write_files(&[(name, std::sync::Arc::new(certificate_pem(c).into_bytes()))], "Export certificate");
+    }
+
     /// Start signing: the rectangle (or field) is known; show Sign with a Digital ID.
     pub fn start_signing(&mut self, page: usize, rect: Option<[f64; 4]>, field: Option<String>, certify: Option<u8>) {
         self.refresh_os_key_store_ids();
@@ -1496,6 +1502,23 @@ mod tests {
         Ok(PathBuf::from(&app.digital_ids[i].path))
     }
 
+    #[test]
+    fn an_exported_certificate_is_written_inside_the_chosen_folder() {
+        let dir = scratch();
+        let out = dir.join("out");
+        std::fs::create_dir_all(&out).unwrap();
+        let key = PrivateKey::generate_p256().unwrap();
+        let cert = Certificate::self_signed(&Name::build("../x", "", "", "", ""), &key, sign::Time::from_unix(0), 1, &[1]).unwrap();
+        let mut app = PdfCraftApp::new();
+        app.export_dir_override = Some(out.to_string_lossy().into_owned());
+        app.export_certificate(&cert);
+        let written: Vec<_> = std::fs::read_dir(&dir).unwrap().map(|e| e.unwrap().file_name()).collect();
+        assert_eq!(written, vec![std::ffi::OsString::from("out")]);
+        let pem = std::fs::read_to_string(out.join(".._x.cer")).unwrap();
+        assert!(pem.starts_with("-----BEGIN CERTIFICATE-----"), "{pem}");
+        let _ = std::fs::remove_dir_all(&dir);
+    }
+
     #[test]
     fn signature_status_style_gives_each_verdict_its_panel_icon() {
         assert_eq!(signature_status_style(SignatureStatus::Valid).0, "circle-check");

crates/ui-egui/tests/pickers.rs

@@ -748,20 +748,26 @@ fn a_background_startup_forms_script_notice_waits_until_its_tab_is_selected() {
 
 /// Embedded bytes and the PDF's original /UF name stay independent of the Save suggestion.
 fn attachment_fixture() -> Vec<u8> {
-    let name = "invoice\u{202e}fdp.exe";
+    attachment_pdf("invoice\u{202e}fdp.exe", b"hello notes")
+}
+
+/// A one-page PDF with one embedded file whose /UF name is `name`.
+fn attachment_pdf(name: &str, data: &[u8]) -> Vec<u8> {
     let uf = std::iter::once(0xfeffu16).chain(name.encode_utf16()).map(|c| format!("{c:04X}")).collect::<String>();
-    let objs = [
+    let objs: [Vec<u8>; 5] = [
-        "<< /Type /Catalog /Pages 2 0 R /Names << /EmbeddedFiles << /Names [(notes.txt) 5 0 R] >> >> >>".to_string(),
+        b"<< /Type /Catalog /Pages 2 0 R /Names << /EmbeddedFiles << /Names [(notes.txt) 5 0 R] >> >> >>".to_vec(),
-        "<< /Type /Pages /Kids [3 0 R] /Count 1 >>".to_string(),
+        b"<< /Type /Pages /Kids [3 0 R] /Count 1 >>".to_vec(),
-        "<< /Type /Page /Parent 2 0 R /MediaBox [0 0 200 200] /Resources << >> >>".to_string(),
+        b"<< /Type /Page /Parent 2 0 R /MediaBox [0 0 200 200] /Resources << >> >>".to_vec(),
-        "<< /Type /EmbeddedFile /Length 11 >>\nstream\nhello notes\nendstream".to_string(),
+        [format!("<< /Type /EmbeddedFile /Length {} >>\nstream\n", data.len()).as_bytes(), data, b"\nendstream"].concat(),
-        format!("<< /Type /Filespec /F (notes.txt) /UF <{uf}> /EF << /F 4 0 R >> >>"),
+        format!("<< /Type /Filespec /F (notes.txt) /UF <{uf}> /EF << /F 4 0 R >> >>").into_bytes(),
     ];
     let mut out = b"%PDF-1.7\n".to_vec();
     let mut offsets = Vec::new();
     for (i, o) in objs.iter().enumerate() {
         offsets.push(out.len());
-        out.extend_from_slice(format!("{} 0 obj\n{o}\nendobj\n", i + 1).as_bytes());
+        out.extend_from_slice(format!("{} 0 obj\n", i + 1).as_bytes());
+        out.extend_from_slice(o);
+        out.extend_from_slice(b"\nendobj\n");
     }
     let xref = out.len();
     out.extend_from_slice(b"xref\n0 6\n0000000000 65535 f \n");
@@ -824,3 +830,42 @@ fn attachment_save_preserves_bytes_metadata_and_selected_destination() {
     assert_eq!(doc.info.attachments[index].name, raw_name);
     assert_eq!(doc.bytes.as_ref(), &original);
 }
+
+/// Every file under `dir`, recursively, sorted.
+fn files_under(dir: &std::path::Path) -> Vec<std::path::PathBuf> {
+    let mut out = Vec::new();
+    for entry in std::fs::read_dir(dir).unwrap() {
+        let path = entry.unwrap().path();
+        if path.is_dir() { out.extend(files_under(&path)) } else { out.push(path) }
+    }
+    out.sort();
+    out
+}
+
+#[test]
+fn files_written_from_an_attachment_tab_stay_inside_the_chosen_folder() {
+    let dir = AttachmentDir::new();
+    let absolute = dir.0.join("elsewhere").join("x.pdf").to_string_lossy().into_owned();
+    for name in ["../../x.pdf", absolute.as_str()] {
+        let out = dir.0.join("a").join("b").join("out");
+        std::fs::create_dir_all(&out).unwrap();
+        let mut h = harness(&[]);
+        h.state_mut().open_bytes("outer.pdf", None, attachment_pdf(name, &fixture(2))).unwrap();
+        h.run_steps(2);
+        let id = h.state().views[0].id;
+        h.state_mut().attachment_action(id, 0, true);
+        h.run_steps(2);
+        assert_eq!(h.state().views.len(), 2, "{name}: the attachment opens as a tab");
+        h.state_mut().export_dir_override = Some(out.to_string_lossy().into_owned());
+        h.state_mut().split_active(&pdfcraft_ui_egui::SplitPlan::By(pdfcraft_engine::SplitBy::PageCount(1)));
+        let written = files_under(&dir.0);
+        assert_eq!(written.len(), 2, "{name}: two split parts, got {written:?}");
+        assert!(written.iter().all(|p| p.parent() == Some(out.as_path())), "{name}: {written:?}");
+        // Extract writes page 1 under the name Split gave it.
+        h.state_mut().extract_draft = pdfcraft_ui_egui::ExtractDraft { separate: true, ..Default::default() };
+        h.state_mut().extract_selection();
+        assert!(h.state().toast.as_ref().is_some_and(|t| t.0.starts_with("Wrote 1 file")), "{name}: {:?}", h.state().toast);
+        assert_eq!(files_under(&dir.0), written, "{name}");
+        std::fs::remove_dir_all(dir.0.join("a")).unwrap();
+    }
+}