# CVE-2026-55407 — anthropics buffa

> As of 2026-07-16, CVE-2026-55407 is a Medium-severity (band derived from the CVSS v4.0 score, not stated by the CNA) vulnerability in anthropics buffa, CVSS v4.0 6.3, EPSS 0.7% (53.7th percentile). Threadlinqs Intelligence links 1 tracked threat campaign to CVE-2026-55407, most recently “CVE-2026-55407: Unbounded Heap Allocation DoS in Anthropic's Buffa Rust Protobuf Library (decode_unknown_field)”.

**Last updated:** 2026-07-16

## What is CVE-2026-55407?

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.

The record classifies CVE-2026-55407 under weakness classes [CWE-400](https://intel.threadlinqs.com/cwe/CWE-400), [CWE-770](https://intel.threadlinqs.com/cwe/CWE-770), [CWE-789](https://cwe.mitre.org/data/definitions/789.html). 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 86 days ago.

## Severity and exploitation probability

- **CVSS v4.0 base score:** 6.3 — Medium (derived from score) (`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`)
- **EPSS (FIRST):** 0.7% probability of exploitation in the next 30 days, higher than 53.7% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 5.3/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-07-16

## Is CVE-2026-55407 being exploited?

It currently carries a trending score of 27 in the Threadlinqs vulnerability feed.

## Affected products and versions

- [anthropics](https://intel.threadlinqs.com/vendors/anthropics): buffa

Affected software packages:

- `rust:buffa` — patched in 0.8.0

## How to fix CVE-2026-55407

Fixed versions are recorded for 1 package: rust:buffa 0.8.0. No vendor patch reference has been recorded for CVE-2026-55407 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

## Threat activity tracking CVE-2026-55407

1 tracked threat in the Threadlinqs corpus references CVE-2026-55407, either in the campaign’s CVE list or as an indicator on the campaign record.

- [CVE-2026-55407: Unbounded Heap Allocation DoS in Anthropic's Buffa Rust Protobuf Library (decode_unknown_field)](https://intel.threadlinqs.com/threat/TL-2026-1039) — MODERATE · 2026-07-01

## Sources

Enriched from CVE.org, FIRST EPSS, GitHub Security Advisories. Last verified by Threadlinqs on 2026-10-10.

**Vendor advisory and patch**

- [github.com](https://github.com/anthropics/buffa/security/advisories/GHSA-f9qc-qg88-7pq5)

**Other references**

- [github.com](https://github.com/anthropics/buffa/pull/184)
- [github.com (278fa43fcff661d4ee6bd83b75955a153d4281fc)](https://github.com/anthropics/buffa/commit/278fa43fcff661d4ee6bd83b75955a153d4281fc)
- [github.com (v0.8)](https://github.com/anthropics/buffa/releases/tag/v0.8.0)

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-55407
Full detection coverage and IOCs for threats exploiting CVE-2026-55407 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp