CVE-2026-102559 Libsoup: libsoup: heap buffer overflow during websocket client-frame masking

High 8.6 Published 29 Sep 2026 Updated 29 Oct 2026

A heap buffer overflow in libsoup's WebSocket masking allows attackers to execute arbitrary code or cause denial of service via large payloads.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: Not needed
Fix: Available

What is CVE-2026-102559?

CVE-2026-102559 is a high-severity memory corruption vulnerability in Redhat Enterprise Linux, published on 29 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official 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.

Weakness: CWE-125

Which versions are affected by CVE-2026-102559?

It affects 2 products.

Products include Gnome Libsoup, Redhat Enterprise Linux.

How do I fix CVE-2026-102559?

Apply the vendor's patch.

Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.

Is CVE-2026-102559 being exploited?

There is no known exploitation of CVE-2026-102559 in the wild and no public exploit code.

All Redhat Enterprise Linux vulnerabilities

Sources

Also known as AZL-105558, DEBIAN-CVE-2026-102559, ECHO-c70c-d13e-fd09, GHSA-cj4p-f4hv-cp74, UBUNTU-CVE-2026-102559.