Images: a WebP with an ICC chunk longer than the file is read without its profile

* Images: a WebP whose ICC chunk declares more than the file holds is read without it

crates/images/src/lib.rs

@@ -433,9 +433,32 @@ pub fn decode_rgba(bytes: &[u8]) -> Option<image::RgbaImage> {
     to_display_rgba(px, Some(&icc), &DisplayColour::active())
 }
 
+/// False when `bytes` is a WebP whose `ICCP` chunk declares more bytes than the file holds or than
+/// [`colour::MAX_ICC_BYTES`]. The decoder sizes its buffer from the declared length before it reads
+/// anything, so such a file must not reach `icc_profile()`; its pixels decode without it.
+pub fn webp_icc_is_sane(bytes: &[u8]) -> bool {
+    if bytes.get(0..4) != Some(b"RIFF") || bytes.get(8..12) != Some(b"WEBP") {
+        return true;
+    }
+    let mut pos = 12usize;
+    while let Some(head) = bytes.get(pos..pos.saturating_add(8)) {
+        let size = u32::from_le_bytes([head[4], head[5], head[6], head[7]]) as usize;
+        let body = pos + 8;
+        if &head[..4] == b"ICCP" {
+            return size <= colour::MAX_ICC_BYTES && body.saturating_add(size) <= bytes.len();
+        }
+        // Chunks are padded to an even size.
+        pos = body.saturating_add(size).saturating_add(size & 1);
+    }
+    true
+}
+
 /// The ICC profile embedded in a PNG, JPEG, TIFF or WebP.
 fn embedded_icc(bytes: &[u8]) -> Option<Vec<u8>> {
     use image::ImageDecoder;
+    if !webp_icc_is_sane(bytes) {
+        return None;
+    }
     let mut d = image::ImageReader::new(std::io::Cursor::new(bytes)).with_guessed_format().ok()?.into_decoder().ok()?;
     d.icc_profile().ok().flatten()
 }

crates/images/src/tests.rs

@@ -534,3 +534,30 @@ fn gif_tone_and_cmyk_inks_check_the_rgba_budget() {
     assert!(too_large_to_decode(&tiff));
     assert_eq!(decode_cmyk_tiff(&tiff), None);
 }
+
+fn webp_with(chunks: &[(&[u8; 4], u32, &[u8])]) -> Vec<u8> {
+    let mut v = b"RIFF\0\0\0\0WEBP".to_vec();
+    for (id, declared, body) in chunks {
+        v.extend_from_slice(*id);
+        v.extend_from_slice(&declared.to_le_bytes());
+        v.extend_from_slice(body);
+        if body.len() % 2 == 1 {
+            v.push(0);
+        }
+    }
+    v
+}
+
+/// A WebP that declares an `ICCP` chunk larger than the file (or than the ICC cap) never reaches the
+/// decoder's profile read, which would size a buffer from the declared length.
+#[test]
+fn a_webp_icc_chunk_that_declares_more_than_it_holds_is_refused_before_decoding() {
+    assert!(webp_icc_is_sane(&webp_with(&[(b"VP8X", 10, &[0; 10]), (b"ICCP", 4, &[1; 4])])));
+    // An odd-sized chunk before it is padded to even.
+    assert!(webp_icc_is_sane(&webp_with(&[(b"EXIF", 3, &[0; 3]), (b"ICCP", 4, &[1; 4])])));
+    assert!(!webp_icc_is_sane(&webp_with(&[(b"VP8X", 10, &[0; 10]), (b"ICCP", u32::MAX, &[1; 4])])));
+    assert!(!webp_icc_is_sane(&webp_with(&[(b"ICCP", 100, &[1; 4])])));
+    assert!(embedded_icc(&webp_with(&[(b"ICCP", u32::MAX, &[1; 4])])).is_none());
+    assert!(webp_icc_is_sane(b"\x89PNG not a webp"));
+    assert!(webp_icc_is_sane(&webp_with(&[(b"VP8L", 6, &[0; 6])])));
+}

crates/pdf/src/export/images.rs

@@ -47,6 +47,9 @@ pub(super) struct RasterMode {
 /// The ICC profile embedded in an image file, if it has one.
 pub(super) fn embedded_icc(data: &[u8]) -> Option<Vec<u8>> {
     use image::ImageDecoder;
+    if !designcraft_images::webp_icc_is_sane(data) {
+        return None;
+    }
     let mut dec = image::ImageReader::new(std::io::Cursor::new(data)).with_guessed_format().ok()?.into_decoder().ok()?;
     dec.icc_profile().ok().flatten()
 }
@@ -89,6 +92,9 @@ pub(super) fn jpeg(data: krilla::Data, icc: impl FnOnce() -> Option<Vec<u8>>, mo
 /// its own.
 fn untagged_rgb(data: &[u8]) -> bool {
     use image::ImageDecoder;
+    if !designcraft_images::webp_icc_is_sane(data) {
+        return false;
+    }
     let Some(mut dec) = image::ImageReader::new(std::io::Cursor::new(data)).with_guessed_format().ok().and_then(|r| r.into_decoder().ok()) else {
         return false;
     };