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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
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.
Which versions are affected by CVE-2026-55407?
2 open source packages ship an affected version, including buffa.
| Package | 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.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-55407 being exploited?
There is no known exploitation of CVE-2026-55407 in the wild and no public exploit code.
Sources
Also known as GHSA-f9qc-qg88-7pq5.