CVE-2026-42772 — Potential CPU DoS via O(n^2) Fragment Reassembly in QUIC

Affected: OpenSSL

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.

USN-8861-1 — openssl vulnerabilities

Affected: Ubuntu:26.04:LTS: openssl

It was discovered that OpenSSL had an inefficient algorithm in its QUIC stream reassembly implementation. A remote attacker could possibly use this issue to cause OpenSSL to use excessive CPU resources, leading to a denial of service. (CVE-2026-42772)

It was discovered that OpenSSL did not properly limit memory allocated for QUIC packet buffers. A remote attacker could possibly use this issue to cause OpenSSL to use excessive memory resources, leading to a denial of service. (CVE-2026-54873)

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CVE-2026-42772 — Potential CPU DoS via O(n^2) Fragment Reassembly in QUIC

USN-8861-1 — openssl vulnerabilities