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

Severity: high (CVSS 8.6 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-09-29 · updated 2026-10-29
Weakness: CWE-125

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.

Affected products

GNOME libsoup: before 3.7.3 — fixed in 3.7.3
Red Hat Enterprise Linux: 7.0, 8.0, 9.0, 10.0 (and their updates)
Red Hat Enterprise Linux 10: all versions — fixed in 0:3.6.5-3.el10_2.20
Red Hat Enterprise Linux 7: all versions
Red Hat Enterprise Linux 8: all versions — fixed in 0:2.62.3-19.el8_10
Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support: all versions — fixed in 0:2.62.3-2.el8_4.14
Red Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-On: all versions — fixed in 0:2.62.3-2.el8_4.14
Red Hat Enterprise Linux 9: all versions — fixed in 0:2.72.0-16.el9_8.8

How to fix

Upgrade to a fixed version: GNOME libsoup 3.7.3; Red Hat Enterprise Linux 10 0:3.6.5-3.el10_2.20; Red Hat Enterprise Linux 8 0:2.62.3-19.el8_10; Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support 0:2.62.3-2.el8_4.14; Red Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-On 0:2.62.3-2.el8_4.14; Red Hat Enterprise Linux 9 0:2.72.0-16.el9_8.8. Check the vendor advisory for mitigations.

References

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