2026-06-30 · 2026-Q2
Anthropic "buffa" Rust protobuf Memory-Amplification DoS (CVE-2026-55407)
Outside the model: AI capability Agent tooling was not the attack surface, so no layer applies.
- Fixable:
- Yes, vendor patch
- Vendor response:
- Patched
- In the wild:
- No
Target
buffa, Anthropic's Rust protobuf library, versions before 0.8.0
Impact
An attacker sending crafted protobuf wire data to any service that decodes untrusted input with the default `preserve_unknown_fields=true` can force unbounded heap allocation; a nested-group path amplifies roughly 22x, so a 64 MiB message triggers about 1.4 GB of allocation and out-of-memory crashes
Root Cause
The `decode_unknown_field` path allocates memory proportional to attacker-controlled data with no per-message field-count limit; the 0.8.0 fix caps unknown fields (default 1 million) and bounds overhead. Found by Endor Labs' AI SAST engine (Peyton Kennedy)