Anthropic buffa Library Zero-Day Lets Attackers Trigger Memory

Gbhackers •Divya • July 1, 2026

Anthropic’s Rust-based protobuf library, buffa, has been discovered to have a zero-day memory amplification denial-of-service (DoS) vulnerability. This flaw allows attackers to deplete system memory using relatively small inputs. Endor Labs identified the issue through its AI-powered static application security testing (SAST) engine and is now tracked as CVE-2026-55407. This situation underscores how logic flaws […]

The full story

This article is one source in a clustered incident — the cluster page carries the summary, timeline and every other outlet covering it.

Zero-Day DoS Vulnerability Found in Anthropic's buffa Library A zero-day memory amplification denial-of-service (DoS) vulnerability has been discovered in Anthropic's Rust-based protobuf library, buffa. Identified as CVE-2026-55407, the flaw allows attackers to exploit unbounded-allocation data flows, leading to significant memory depletion with small inputs. Endor Labs' AI-powered static application security testing (SAST) engine detected the issue, which affects any message decoded from untrusted input using the default settings. The vulnerability is linked to the decode_unknown_field function in buffa's encoding module, where the allocation size is derived directly from untrusted input. Anthropic has engaged with Endor Labs following the disclosure to assess the severity based on deployment scenarios. The vulnerability is classified as moderate with a CVSS score of 6.3. Immediate action is advised for users of the library to mitigate potential impacts. 3 sources 58

Extracted Entities

Attack Types (1)

Denial of Service

CVEs (1)

CVE-2026-55407