TI-2026-39977 Aliases CVE-2026-55407 GHSA-f9qc-qg88-7pq5

Buffa: Memory Exhaustion Denial of Service in decode_unknown_field via Unbounded Allocation

LOW 29CWE-400Published 2026-07-16 · Updated 2026-07-16

Key facts

Attack vector: Network
Privileges required: None
User interaction: None
Attack complexity: Low
Attack requirements: Present
Impact type: Denial of service
Confidentiality · integrity · availability: None · None · Low
Fix status: Fixed

Attack profile from CVSS 4.0 · CNA. Fix status from CNA and GitHub. Impact type from CWE-400.

Summary

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV

EPSS 0.00755 55th percentileScored 2026-11-07

Fix Fixed buffa (anthropics): 0.8.0buffa (crates.io): 0.8.0

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation: None
Automatable: No
Technical impact: Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

Vendor	Product	Affected versions	Fixed in	Status	Source
anthropics	buffa	before 0.8.0	0.8.0	Patch available	CNA
—	buffa (crates.io)	before 0.8.0	0.8.0	Patch available	GHSA-f9qc-qg88-7pq5

buffa Vendoranthropics Affected before 0.8.0 Fixed in 0.8.0 Patch available CNA
buffa (crates.io) Vendor— Affected before 0.8.0 Fixed in 0.8.0 Patch available GHSA-f9qc-qg88-7pq5

Remediation

Fix · CNA buffa (anthropics) Fixed in 0.8.0
Fix · GHSA-f9qc-qg88-7pq5 buffa (crates.io) Fixed in 0.8.0 Advisory →

Timeline

2026-10-02 Threatist record created from CVE-2026-55407
2026-10-03 Alias added: GHSA-f9qc-qg88-7pq5

References

Advisory 1

https://nvd.nist.gov/vuln/detail/CVE-2026-55407

Other 5

TI-2026-79288 Out-of-bounds write in Google Brotli decoder KEVCVSS 4.0CRITICAL 9.2
TI-2026-00421 MCP TypeScript SDK UriTemplate Exploded Array Pattern ReDoS CVSS 4.0HIGH 8.7
TI-2025-40558 Claude Code Command Validation Bypass Allows Arbitrary Code Execution CVSS 4.0HIGH 8.7
TI-2025-36683 Claude Code vulnerable to arbitrary code execution caused by maliciously configured git email CVSS 4.0HIGH 8.7
TI-2025-24240 Anthropic Slack MCP Server Data Exfiltration via Link Unfurling CVSS 4.0CRITICAL 9.3
TI-2025-32918 Claude Code IDE extensions allow websocket connections from arbitrary origins CVSS 4.0HIGH 8.8

See all 46 →

Sources

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