Critical libwebp Vulnerability Under Active Exploitation – Gets Maximum CVSS Score


Google has assigned a new CVE identifier for a critical security flaw in the libwebp image library for rendering images in the WebP format that has come under active exploitation in the wild.

Tracked as CVE-2023-5129, the issue has been given the maximum severity score of 10.0 on the CVSS rating system. It has been described as an issue rooted in the Huffman coding algorithm –

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.

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