# Buffa Vulnerable to Memory Exhaustion Denial of Service in decode_unknown_field via Unbounded Allocation

Advisory record · `GHSA-f9qc-qg88-7pq5`

- **Identifiers:** `GHSA-f9qc-qg88-7pq5` · `CVE-2026-55407`
- **State:** Confirmed
- **Severity:** CVSS 6.3 Medium
- **Critical:** No
- **Weakness (CWE):** [CWE-400](https://cwe.mitre.org/data/definitions/400.html) · [CWE-770](https://cwe.mitre.org/data/definitions/770.html) · [CWE-789](https://cwe.mitre.org/data/definitions/789.html)
- **Tags:** [Denial of service](https://agentprime.io/advisories/tag/dos.md)
- **Published:** 28 Aug 2026
- **Updated:** 28 Aug 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 28 Aug 2026, 18:34 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `buffa` (crates.io): affected `<0.8.0`; fixed in `0.8.0`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> Buffa versions before 0.8.0 are vulnerable to memory exhaustion in the decode_unknown_field function, which allocates memory in proportion to unknown fields in untrusted protobuf input without an allocation budget. An unauthenticated attacker can send a small crafted payload to any message decoded with code generated using preserve_unknown_fields=true (the default), causing a large heap allocation that can crash the process. Upgrade to buffa 0.8.0, which enforces per-message unknown field count limits, or set preserve_unknown_fields=false in generated code.

Written 8 Nov 2026.

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 6.3 Medium, CVSS 4.0: `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`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0076, the 55th percentile, on 8 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 15:18 UTC: First seen by agentprime
- 31 Oct 2026, 15:18 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-f9qc-qg88-7pq5)

## Sources

- [GitHub Advisory Database: GHSA-f9qc-qg88-7pq5](https://github.com/advisories/GHSA-f9qc-qg88-7pq5)
- [OSV: GHSA-f9qc-qg88-7pq5](https://osv.dev/vulnerability/GHSA-f9qc-qg88-7pq5)
- <https://github.com/anthropics/buffa/security/advisories/GHSA-f9qc-qg88-7pq5>
- <https://nvd.nist.gov/vuln/detail/CVE-2026-55407>
- <https://github.com/anthropics/buffa/pull/184>
- <https://github.com/anthropics/buffa/commit/278fa43fcff661d4ee6bd83b75955a153d4281fc>
- <https://github.com/anthropics/buffa>
- <https://github.com/anthropics/buffa/releases/tag/v0.8.0>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-f9qc-qg88-7pq5>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-f9qc-qg88-7pq5/>. Everything for agents: <https://agentprime.io/llms.txt>.