With a specially crafted WebP lossless file, libwebp may write data out of bounds to the heap.

The ReadHuffmanCodes() function allocates the HuffmanCode buffer with a size that comes from an array of precomputed sizes: kTableSize. The color_cache_bits value defines which size to use.

The kTableSize array only takes into account sizes for 8-bit first-level table lookups but not second-level table lookups. libwebp allows codes that are up to 15-bit (MAX_ALLOWED_CODE_LENGTH). When BuildHuffmanTable() attempts to fill the second-level tables it may write data out-of-bounds. The OOB write to the undersized array happens in ReplicateValue.

References

• https://nvd.nist.gov/vuln/detail/CVE-2023-5129
• https://chromium.googlesource.com/webm/libwebp/+/2af26267cdfcb63a88e5c74a85927a12d6ca1d76
• https://chromium.googlesource.com/webm/libwebp/+/902bc9190331343b2017211debcec8d2ab87e17a