CVE-2026-85670

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CVE-2026-85670

Summary: tokenizers BpeBuilder Buffer Overflow via merge token

Details: tokenizers (Hugging Face) is affected by an out-of-bounds buffer access in BpeBuilder::build (tokenizers/src/models/bpe/model.rs). When loading a tokenizer.json via Tokenizer::from_file/from_str, the builder sizes a scratch buffer to the longest vocabulary key, then writes each concatenated merge rule into it. A merge whose concatenated token exceeds the longest vocabulary key overruns the buffer, which Rust turns into a panic that aborts the process in Rust and FFI embeddings. This occurs at load time with no encoding required, so an attacker who supplies a crafted tokenizer.json can cause a denial of service. A secondary defect at the same location can cause a usize underflow (panic in debug, potential memory corruption in release) when continuing_subword_prefix is set and a merge token is shorter than the prefix. Observed in version 0.23.1.

References: https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/85xxx/CVE-2026-85670.json, https://nvd.nist.gov/vuln/detail/CVE-2026-85670, https://www.vulncheck.com/advisories/tokenizers-bpebuilder-buffer-overflow-via-merge-token, https://github.com/huggingface/tokenizers/issues/2094, https://github.com/huggingface/tokenizers, https://github.com/huggingface/tokenizers/blob/v0.23.2/tokenizers/src/models/bpe/model.rs