Libsoup: libsoup: heap buffer overflow during websocket client-frame masking (CVE-2026-102559) | HOL Guard CVE

High · CVSS 8.6CVE-2026-102559

Libsoup: libsoup: heap buffer overflow during websocket client-frame masking

Answer in brief

CVE-2026-102559 records a High severity (CVSS 8.6) vulnerability in Libsoup: libsoup: heap buffer overflow during websocket client-frame masking. The current sources do not mark it as known exploited. The current feed maps Red Hat/libsoup (generic), Red Hat/libsoup3 (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 29, 2026Updated Sep 29, 2026Source checked Sep 29, 2026First seen by HOL Sep 29, 2026Material review Sep 29, 2026

Upstream Advisory

Key facts

Risk: High · CVSS 8.6
Exploitation: Not marked as known exploited
Affected software: 2 mapped packages or products
Fix availability: Not reported

Why this deserves its current priority

CVSS is 8.6. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Red Hat/libsoup (generic), Red Hat/libsoup3 (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Red Hat/libsoupgeneric	*	Not reported
Red Hat/libsoup3generic	*	Not reported

Recommended response

Check inventory. Check lockfiles and deployed manifests for Red Hat/libsoup, Red Hat/libsoup3.
Review the reported fix. Source-reported workaround: To mitigate this enforce application-level limits on outgoing WebSocket message sizes. Do not send untrusted bulk data as a single WebSocket message.

Evidence timeline and material changes

Published upstream
Sep 29, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 29, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 29, 2026

Sources and claim methodology

Upstream source description

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.

Quoted source text, attributed separately from HOL analysis.