Endor Labs’ AI SAST Finds Zero Day Memory-Amplification DoS in Anthropic’s buffa library | Endor Labs

Summary

Endor Labs reports that its AI SAST engine flagged an unbounded-allocation flow in decode_unknown_field in buffa/src/encoding.rs, the protobuf decoder in Anthropic's Rust library buffa. A length prefix from untrusted wire data sizes a Vec<u8> allocation with no bound beyond fitting in a usize, and the researchers extended it to a memory-amplification denial of service of about 22x, tracked as GHSA-f9qc-qg88-7pq5 / CVE-2026-55407 (CVSS 4.0 6.3). Any message decoded from untrusted input with preserve_unknown_fields=true, the default, was affected.

Mitigation

Fixed in buffa and connectrpc 0.8.0 (affected versions are below 0.8.0).

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