Threats tagged 'ghsa-462x-pgg6-55fp'

### Summary Pillow's libImaging `_decodeTile` decoder, used to decode tiled TIFF images, allocates a per-tile buffer using `realloc(state->buffer, TIFFTileSize(tiff))`. After each `TIFFReadTile` it then iterates `tile_y` from 0 up to `current_tile_length` and calls the configured row unpacker (here `copy4`) with the source pointer `state->buffer + tile_y * row_byte_size`. When libtiff returns a `tile_bytes_size` smaller than the worst-case `row_byte_size * tile_length`, the inner stride-and-copy loop walks past the realloc'd region and `copy4` performs a 1024-byte `memcpy` that reads up to `(tile_length-1) * row_byte_size + row_byte_size` bytes from a buffer sized only to `tile_bytes_size`. The supplied PoC TIFF triggers a 1024-byte over-read exactly 0 bytes past a 196608-byte allocation. An attacker who can convince a Pillow-using application to decode a crafted TIFF can trigger a process crash (DoS) and may cause adjacent heap memory to be copied into the decoded pixel buffer. ### Details Pillow's TIFF decoder, when libtiff reports the file is tiled, takes the `_decodeTile` path. The function: 1. Asks libtiff for `TIFFTileSize(tiff)` (the bytes-per-tile) and `TIFFTileRowSize(tiff)` (the bytes per row *as stored by libtiff*). 2. Reallocates `state->buffer` to exactly `tile_bytes_size`. 3. For each tile origin `(x, y)` and each plane, calls `TIFFReadTile` into `state->buffer`, then walks the tile row by row, calling the configured `ImagingShuffler` (here `copy4`) on each row's worth of source bytes. The validation done before the loop is: ```c if (tile_bytes_size > ((tile_length * state->bits / planes + 7) / 8) * tile_width) { state->errcode = IMAGING_CODEC_BROKEN; return -1; } ``` This rejects oversized libtiff tiles, but it does **not** reject *undersized* ones — i.e. the case where libtiff returns a `tile_bytes_size` strictly **less** than `row_byte_size * tile_length`. The loop body, however, indexes into the buffer assuming the buffer is at least `row_byte_size * tile_length` bytes long. ### Vulnerable Code ```c // src/libImaging/TiffDecode.c:446-490 — _decodeTile new_data = realloc(state->buffer, state->bytes); // bytes = tile_bytes_size if (!new_data) { ... } state->buffer = new_data; for (y = state->yoff; y < state->ysize; y += tile_length) { for (plane = 0; plane < planes; plane++) { ImagingShuffler shuffler = unpackers[plane]; for (x = state->xoff; x < state->xsize; x += tile_width) { if (TIFFReadTile(tiff, (tdata_t)state->buffer, x, y, 0, plane) == -1) { ... } current_tile_width = min((INT32)tile_width, state->xsize - x); current_tile_length = min((INT32)tile_length, state->ysize - y); for (tile_y = 0; tile_y < current_tile_length; tile_y++) { shuffler( (UINT8 *)im->image[tile_y + y] + x * im->pixelsize, state->buffer + tile_y * row_byte_size, // <-- OOB stride current_tile_width ); } } } } ``` ```c // src/libImaging/Unpack.c:1288-1291 — copy4 (the crash site) static void copy4(UINT8 *out, const UINT8 *in, int pixels) { /* RGBA, CMYK quadruples */ memcpy(out, in, 4 * pixels); // <-- ASAN-detected READ here } ``` The PoC's tile metadata yields `tile_width = tile_length = 256`, `row_byte_size = 1024` (4 bytes/pixel × 256 pixels), and `tile_bytes_size = 196608` (which is 256·256·3 = three-channel-byte storage). The realloc'd buffer is 196608 bytes. The unpacker iterates `tile_y` from 0 to 255 and for the highest rows the source pointer `state->buffer + tile_y * 1024` already lies at or past offset 196608 — the very last row's `memcpy(in=buffer+255·1024, 1024)` reads 1024 bytes starting `260096 - 196608 = 63488` bytes past the allocation; ASAN flags the very first byte past the heap region (`READ of size 1024 at … 0 bytes after 196608-byte region`). The mismatch is real: libtiff's `TIFFTileSize` returns the *packed* per-tile storage (which depends on the file's photometric/separation layout — it can legitimately be smaller than `row_byte_size × tile_length`), while the inner loop strides as if the buffer always equals `row_byte_size × tile_length`. ## Attribution This issue was found by Anthropic from using Claude to study security of open source projects, and I am from Ada Logics helping validate the found issues and report to maintainers. The data in this report has been reviewed manually.