CVE-2026-112404

Pillow is a Python imaging library. From 8.1.0 until 13.0.0, Pillow's TIFF tile and RGBA decode paths can read beyond row data produced by libtiff. In _decodeTile and the RGBA unpacker path, when Pillow and libtiff interpret duplicated PhotometricInterpretation or BitsPerSample tags differently, Pillow does not verify that the required input row fits inside the row libtiff produced, while the strip path has this validation. Loading pixels from such a crafted TIFF can expose adjacent heap data in output pixels or crash the process. This issue is fixed in version 13.0.0.

Pillow is a Python imaging library. From 8.1.0 until 13.0.0, Pillow's TIFF tile and RGBA decode paths can read beyond row data produced by libtiff. In _decodeTile and the RGBA unpacker path, when Pillow and libtiff interpret duplicated PhotometricInterpretation or BitsPerSample tags differently, Pillow does not verify that the required input row fits inside the row libtiff produced, while the strip path has this validation. Loading pixels from such a crafted TIFF can expose adjacent heap data in output pixels or crash the process. This issue is fixed in version 13.0.0.

============================================================================
OOB read in TiffDecode.c tile and RGBA paths leaks heap memory into pixels
Location: src/libImaging/TiffDecode.c:483  in _decodeTile()
Commit:   a707c6b21c313880d0771e54965d142dd42358b6
============================================================================

Pillow reads past the end of a heap buffer when decoding certain malformed compressed TIFF files, and copies the bytes it reads into the pixels of the image it returns. An attacker who can get an application to open and load an image file, for example by uploading it to a service that returns thumbnails, previews or converted images, gets back fragments of that process's heap memory, including pointer values. A slightly larger file instead crashes the process. No special settings are needed, and nothing is written out of bounds.

The bug is in _decodeTile() and _decodeAsRGBA() in src/libImaging/TiffDecode.c. Both size their decode buffer from libtiff's view of the pixel layout (TIFFTileSize()/TIFFTileRowSize(), or img.width * 4). They then unpack each row with the unpacker that TiffImagePlugin._setup() chose from Pillow's own parse of the directory, and neither checks that the unpacker's input row fits inside the row libtiff produced. _decodeStrip() has exactly this check, added for OSS-Fuzz crash-0da0 in 8.2.0, but the tile and RGBA paths never got it.

The two parsers can be made to disagree with a duplicated PhotometricInterpretation or BitsPerSample tag, because libtiff keeps the first occurrence and Pillow keeps the last. Pillow then unpacks 4 to 8 bytes per pixel from rows that libtiff filled with 1 to 4 bytes, so the last rows of each tile are read from beyond the buffer. The disclosed memory is a few tile rows past the buffer, and the attacker chooses the tile width. The amount does not grow with the number of tiles, because the buffer is reused for every tile.

The tile half was introduced in 1c295bf43 (first released in 8.2.0). The RGBA half was introduced in eb8c1206d, the CVE-2020-35654 fix (8.1.0).

The attached reproducer runs against an unmodified build. It writes three roughly 400-byte files that load without error, yet the last pixel rows of each change with glibc's malloc fill pattern and contain heap pointer bytes. A fourth file with a 65536x16 tile segfaults in copy4 ← _decodeTile (TiffDecode.c:483) in most runs, depending on what is mapped after the buffer.

Details

_decodeTile() and _decodeAsRGBA() in src/libImaging/TiffDecode.c size state->buffer from what libtiff says it will produce (TIFFTileSize(), resp. img.width * 4), but unpack each row with the shuffler that TiffImagePlugin._setup() selected from Pillow's own parse of the IFD. Nothing in either function checks that the unpacker's input row (width * state->bits / 8 bytes) fits inside the row libtiff wrote. _decodeStrip() has exactly that check; the other two do not. Whenever the two IFD parsers disagree about the pixel layout — a tag with the wrong count or type that libtiff ignores but Pillow accepts, or a duplicated PhotometricInterpretation/BitsPerSample/SamplesPerPixel entry (libtiff keeps the first occurrence, ImageFileDirectory_v2.load() the last) — the unpacker reads past the end of the heap buffer and the bytes it reads become pixels of the returned image. Any Pillow rawmode wider than libtiff's actual sample layout works (RGBX, RGB;16N, RGBA;16N, I;32, F;32F, …); RGBA;16N (64 bits/pixel) against 1-bit libtiff data is the largest ratio, where every row after the first of each tile is read almost entirely from beyond the buffer.

The ~400-byte TIFF tile_count2.tif generated by the reproducer — one 16x16 tile, BitsPerSample 8, SamplesPerPixel 1, Compression 8 (Adobe Deflate), and PhotometricInterpretation written as a SHORT with count 2 (6, 6) — is opened by Image.open() as mode RGB with libtiff…

Pillow is a Python imaging library. From 8.1.0 until 13.0.0, Pillow's TIFF tile and RGBA decode paths can read beyond row data produced by libtiff. In _decodeTile and the RGBA unpacker path, when Pillow and libtiff interpret duplicated PhotometricInterpretation or BitsPerSample tags differently, Pillow does not verify that the required input row fits inside the row libtiff produced, while the strip path has this validation. Loading pixels from such a crafted TIFF can expose adjacent heap data in output pixels or crash the process. This issue is fixed in version 13.0.0.

Pillow is a Python imaging library. From 8.1.0 until 13.0.0, Pillow's TIFF tile and RGBA decode paths can read beyond row data produced by libtiff. In _decodeTile and the RGBA unpacker path, when Pillow and libtiff interpret duplicated PhotometricInterpretation or BitsPerSample tags differently, Pillow does not verify that the required input row fits inside the row libtiff produced, while the strip path has this validation. Loading pixels from such a crafted TIFF can expose adjacent heap data in output pixels or crash the process. This issue is fixed in version 13.0.0.

Pillow is a Python imaging library. From 8.1.0 until 13.0.0, Pillow's TIFF tile and RGBA decode paths can read beyond row data produced by libtiff. In _decodeTile and the RGBA unpacker path, when Pillow and libtiff interpret duplicated PhotometricInterpretation or BitsPerSample tags differently, Pillow does not verify that the required input row fits inside the row libtiff produced, while the strip path has this validation. Loading pixels from such a crafted TIFF can expose adjacent heap data in output pixels or crash the process. This issue is fixed in version 13.0.0.