# CVE-2026-55407: Buffa: Memory Exhaustion Denial of Service in decode_unknown_field via Unbounded Allocation

> An unauthenticated attacker can crash a process using the Buffa Rust library by sending a small, crafted protobuf payload that causes excessive memory allocation.

- **Severity:** Medium 6.3 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 16 Jul 2026
- **Updated:** 16 Jul 2026
- **Also known as:** GHSA-f9qc-qg88-7pq5

## What is CVE-2026-55407?

CVE-2026-55407 is a medium-severity denial of service vulnerability in anthropics buffa, published on 16 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-789 (Memory Allocation with Excessive Size Value), CWE-770 (Allocation of Resources Without Limits or Throttling), CWE-400 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2026-55407?

2 open source packages ship an affected version, including buffa.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `buffa` | crates.io | All versions | 0.8.0 |
| `buffa` | crates.io | All versions | 0.8.0 |

## How do I fix CVE-2026-55407?

Upgrade buffa to 0.8.0 or later.

## Is CVE-2026-55407 being exploited?

There is no known exploitation of CVE-2026-55407 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-55407 and fix it if it is affected.

What it is: CVE-2026-55407 is a medium-severity denial of service vulnerability in anthropics buffa, published on 16 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-55407 in the wild and no public exploit code.

Affected packages and fixed versions:
- buffa (crates.io): affected all versions; fixed in 0.8.0
- buffa (crates.io): affected all versions; fixed in 0.8.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-55407/ (Markdown: https://insights.sbomify.com/CVE-2026-55407/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-55407
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-55407
- OSV: https://osv.dev/vulnerability/CVE-2026-55407

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-55407/
Summaries are generated and may contain mistakes; the official description above is the record.