---
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: medium
cvss: 5.3
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L'
cwe:
  - CWE-407
  - CWE-770
vendor: openssl
product: openssl
affected:
  - 'openssl >= 3.4.0, < 3.4.8'
  - 'openssl >= 3.5.0, < 3.5.9'
  - 'openssl >= 3.6.0, < 3.6.5'
  - 'openssl >= 4.0.0, < 4.0.3'
patched:
  - openssl 4.0.3
published: '2026-09-29'
updated: '2026-10-08'
sourceUpdated: '2026-10-08T01:18:57.547'
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
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-42772.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-42772'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2543249'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-42772'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-42772'
  - url: 'https://access.redhat.com/errata/RHSA-2026:74162'
  - url: 'https://access.redhat.com/errata/RHSA-2026:74166'
tags:
  - nvd
  - cve.org
  - csaf
  - vex
  - red-hat
epss: 0.00479
epssPercentile: 0.41154
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-09-30T19:35:54.157005Z'
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.

## Affected

- `openssl >= 3.4.0, < 3.4.8`
- `openssl >= 3.5.0, < 3.5.9`
- `openssl >= 3.6.0, < 3.6.5`
- `openssl >= 4.0.0, < 4.0.3`

## Remediation

Upgrade past the affected range:

- `openssl 4.0.3`

## Vendor advisories

- **Red Hat VEX** · Moderate · affected: Red Hat Developer Hub, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4, Red Hat Satellite 6 · no fix planned: Red Hat Developer Hub, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4, … · updated 2026-10-21 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-42772.json)
- **RHSA-2026:74162** · Red Hat · fixed in: Red Hat Hardened Images · released 2026-09-30 · [advisory](https://access.redhat.com/errata/RHSA-2026:74162)
- **RHSA-2026:74166** · Red Hat · fixed in: Red Hat Hardened Images · released 2026-09-30 · [advisory](https://access.redhat.com/errata/RHSA-2026:74166)