---
id: CVE-2026-42772
title: |-
  Issue summary: The QUIC stream reassembly algorithm performance deteriorates
  progressively as packets are arriving out of order
summary: |-
  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…
severity: none
cwe:
  - CWE-407
vendor: OpenSSL
product: OpenSSL
affected:
  - OpenSSL >= 4.0.0 < 4.0.3
  - OpenSSL >= 3.6.0 < 3.6.5
  - OpenSSL >= 3.5.0 < 3.5.9
  - OpenSSL >= 3.4.0 < 3.4.8
published: '2026-09-29'
updated: '2026-09-29'
sourceUpdated: '2026-09-29T16:17:07.640'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-42772'
references:
  - url: >-
      https://github.com/openssl/openssl/commit/32d0ed8afe1b8c3e7ece725b44663da3d7087a09
    label: openssl-security@openssl.org
  - url: >-
      https://github.com/openssl/openssl/commit/ca8402e273af4de5b3f04fa61a0f0c02ce3ae20e
    label: openssl-security@openssl.org
  - url: >-
      https://github.com/openssl/openssl/commit/eb2becc0a4baea7f3050a247834d0e5c2ebe1773
    label: openssl-security@openssl.org
  - url: >-
      https://github.com/openssl/openssl/commit/f42ae513bbda513b3c121d54834040ee4a0eae1a
    label: openssl-security@openssl.org
  - url: 'https://openssl-library.org/news/secadv/20260929.txt'
    label: openssl-security@openssl.org
tags:
  - nvd
  - cve.org
ingestedAt: '2026-09-29T16:39:33.265Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.