CVE-2026-42772: OpenSSL

Medium severity, CVSS 5.3. EPSS: 0.3% chance of exploitation in the next 30 days.

Issue summary: The QUIC stream reassembly algorithm performance deteriorates progressively as packets are arriving out of order. The worst case has a quadratic complexity proportional to the number of stream frames kept in the buffer for the received stream data. Impact summary: A remote QUIC peer that completes the handshake can create a connection-scoped CPU pressure and potentially a Denial of Service using compliant STREAM frames inside the advertised receive window, with low attacker bandwidth. CWE: CWE-407: Inefficient Algorithmic Complexity Description: OpenSSL manages received QUIC stream fragments using a doubly-linked list. While it optimizes for append operations (at the end of the list), it falls back to a head-to-tail linear search for any fragment that does not immediately follow the current `tail`. By manipulating the sequence of offsets, an attacker can force the server to perform O(n^2) operations, consuming excessive CPU time for the QUIC process. FIPS impact: no The FIPS module is not affected as the QUIC implementation is outside of the OpenSSL FIPS module boundary.

Affected products

• OpenSSL OpenSSL: from 3.4.0, before 3.4.8 (fixed in 3.4.8); from 3.5.0, before 3.5.9 (fixed in 3.5.9); from 3.6.0, before 3.6.5 (fixed in 3.6.5); from 4.0.0, before 4.0.3 (fixed in 4.0.3)

Published 2026-09-29. Last modified 2026-10-08.