CVE-2026-35191 Affecting openssl package, versions <3.6.5-1
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-DEBIANUNSTABLE-OPENSSL-20267512
- published30 Sept 2026
- disclosed29 Sept 2026
Introduced: 29 Sep 2026
NewCVE-2026-35191 (opens in a new tab)How to fix?
Upgrade Debian:unstable openssl to version 3.6.5-1 or higher.
NVD Description
Note: Versions mentioned in the description apply only to the upstream openssl package and not the openssl package as distributed by Debian.
See How to fix? for Debian:unstable relevant fixed versions and status.
Issue summary: The OpenSSL QUIC server, when configured to not preform address validation, can be forced to count incoming packets multiple times in its unvalidated credit computation, leading to a violation of the RFC 9000 unvalidated connection amplification limit of 3 times the amount of data received.
Impact summary: A remote attacker able to spoof packets to a server using the OpenSSL QUIC implementation might use the server for an amplification of a DDoS attack.
CWE: CWE-440: Expected Behavior Violation
Description: OpenSSL's QUIC stack, when operating as a server, enforces client address validation (RFC 9000, Section 8), to confirm the peer address is not used for a traffic amplification attack. If this feature is disabled on the server, the QUIC stack limits the amount of server data that can be sent to 3 times the amount of data received from the peer address, until such time as the TLS handshake is completed.
The OpenSSL QUIC server, when operating in non-validation mode, adds the length of the whole datagram received to the unvalidated credit limit when processing each QUIC packet in the datagram. A remote peer may, after establishing a connection with an initial client hello frame, send a subsequent datagram containing multiple QUIC packets, leading the server to account the entire datagram length for each packet in the datagram, resulting in the server believing that the peer has sent more data than it actually has, thereby violating the 3x amplification limit mandated by the RFC.
FIPS impact: no As the QUIC stack lives outside the FIPS module boundary, no FIPS modules are affected by this CVE.
References
- https://security-tracker.debian.org/tracker/CVE-2026-35191
- https://github.com/openssl/openssl/commit/0fe4442d4f8ea3af8a174046dae176e0d4717239
- https://github.com/openssl/openssl/commit/2de4c35fb13fc58f43fd8dc1d261700472ce72e5
- https://github.com/openssl/openssl/commit/e44292e58b090014232ef75bd400393851b24d1a
- https://openssl-library.org/news/secadv/20260929.txt