---
id: CVE-2026-102559
title: 'Libsoup: libsoup: heap buffer overflow during websocket client-frame masking'
summary: >-
  A flaw was found in libsoup. When constructing a masked WebSocket client frame
  for a very large outgoing payload, size values passed to GByteArray allocation
  APIs could be truncated while the masking routine still used the full length,
  c…
severity: high
cvss: 8.6
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H'
cvssSource: cna
cwe:
  - CWE-125
vendor: Red Hat
product: libsoup3
affected:
  - libsoup3 (all versions)
  - libsoup
  - libsoup (all versions)
  - libsoup (all versions)
  - libsoup (all versions)
published: '2026-09-29'
updated: '2026-09-29'
sourceUpdated: '2026-09-29T17:15:34.470Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-102559'
references:
  - url: 'https://access.redhat.com/security/cve/CVE-2026-102559'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2543285'
    label: RHBZ#2543285
tags:
  - cve.org
ingestedAt: '2026-09-29T17:41:02.260Z'
---

## Overview

A flaw was found in libsoup. When constructing a masked WebSocket client frame for a very large outgoing payload, size values passed to GByteArray allocation APIs could be truncated while the masking routine still used the full length, causing a heap buffer overflow.

## Affected

- `libsoup3 (all versions)`
- `libsoup`
- `libsoup (all versions)`
- `libsoup (all versions)`
- `libsoup (all versions)`

## Remediation

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

### Workarounds

To mitigate this enforce application-level limits on outgoing WebSocket message sizes. Do not send untrusted bulk data as a single WebSocket message.