Bug 2571769 (CVE-2026-119236)

Summary: CVE-2026-119236 mvfst: mvfst: Denial of Service via unbounded memory allocation during handshake processing
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
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Priority: high    
Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in mvfst. A remote, unauthenticated attacker can cause a Denial of Service (DoS) by withholding handshake acknowledgments while continuously transmitting cryptographic frame data. Because the server treats this obsolete handshake data as delivered, it bypasses stream buffer limits, leading to unbounded memory consumption and causing the service to crash.
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Description OSIDB Bzimport 2026-11-11 17:01:16 UTC 
An mvfst QUIC server retained CRYPTO frame data received at an encryption level (Initial or Handshake) that the TLS handshake had already moved past. Because the transport treated this data as delivered, it did not count against the CRYPTO stream buffer limit. A remote, unauthenticated client could complete a handshake, withhold its acknowledgment of the server's HANDSHAKE_DONE frame so that Handshake keys stay in use, and keep sending Handshake-level CRYPTO data at increasing offsets, causing unbounded memory growth on the server and leading to denial of service. This issue affects mvfst versions prior to v2026.11.09.00.