CVE-2026-33999: Xorg: xwayland: x.org x server: denial of service via integer underflow in xkb compatibility map handling

Severity: high (CVSS 7.8 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: 2026-04-23 · updated 2026-10-26
Weakness: CWE-191

Description

A flaw was found in the X.Org X server. This integer underflow vulnerability, specifically in the XKB compatibility map handling, allows an attacker with local or remote X11 server access to trigger a buffer read overrun. This can lead to memory-safety violations and potentially a denial of service (DoS) or other severe impacts.

Affected products

Red Hat Enterprise Linux 10: all versions — fixed in 0:24.1.5-6.el10_1, 0:24.1.9-4.el10_2
Red Hat Enterprise Linux 10.0 Extended Update Support: all versions — fixed in 0:24.1.5-6.el10_0
Red Hat Enterprise Linux 6 Extended Lifecycle Support - EXTENSION: all versions — fixed in 0:1.1.0-25.el6_10.16
Red Hat Enterprise Linux 7 Extended Lifecycle Support: all versions — fixed in 0:1.20.4-34.el7_9, 0:1.8.0-36.el7_9.4
Red Hat Enterprise Linux 8: all versions — fixed in 0:1.15.0-9.el8_10, 0:1.20.11-28.el8_10, 0:21.1.3-20.el8_10
Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support: all versions — fixed in 0:1.11.0-8.el8_4.15, 0:1.20.10-4.el8_4
Red Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-On: all versions — fixed in 0:1.11.0-8.el8_4.15, 0:1.20.10-4.el8_4
Red Hat Enterprise Linux 8.6 Advanced Mission Critical Update Support: all versions — fixed in 0:1.12.0-6.el8_6.17, 0:1.20.11-7.el8_6, 0:21.1.3-2.el8_6.6
Red Hat Enterprise Linux 8.6 Extended Update Support Long-Life Add-On: all versions — fixed in 0:1.12.0-6.el8_6.17
Red Hat Enterprise Linux 8.6 Telecommunications Update Service: all versions — fixed in 0:1.20.11-7.el8_6, 0:21.1.3-2.el8_6.6
Red Hat Enterprise Linux 8.6 Update Services for SAP Solutions: all versions — fixed in 0:1.20.11-7.el8_6, 0:21.1.3-2.el8_6.6
Red Hat Enterprise Linux 8.8 Telecommunications Update Service: all versions — fixed in 0:1.12.0-15.el8_8.17, 0:1.20.11-18.el8_8, 0:21.1.3-13.el8_8
Red Hat Enterprise Linux 8.8 Update Services for SAP Solutions: all versions — fixed in 0:1.12.0-15.el8_8.17, 0:1.20.11-18.el8_8, 0:21.1.3-13.el8_8
Red Hat Enterprise Linux 9: all versions — fixed in 0:1.15.0-6.el9_7.1, 0:1.15.0-7.el9_8.1, 0:1.20.11-33.el9_7, 0:1.20.11-34.el9_8, 0:23.2.7-6.el9_7, 0:24.1.9-4.el9_8
Red Hat Enterprise Linux 9.0 Update Services for SAP Solutions: all versions — fixed in 0:1.11.0-22.el9_0.17, 0:1.20.11-13.el9_0, 0:21.1.3-5.el9_0
Red Hat Enterprise Linux 9.2 Update Services for SAP Solutions: all versions — fixed in 0:1.12.0-14.el9_2.14, 0:1.20.11-20.el9_2, 0:21.1.3-10.el9_2
Red Hat Enterprise Linux 9.4 Extended Update Support: all versions — fixed in 0:1.13.1-8.el9_4.9, 0:1.20.11-28.el9_4, 0:22.1.9-8.el9_4
Red Hat Enterprise Linux 9.6 Extended Update Support: all versions — fixed in 0:1.14.1-10.el9_6, 0:1.20.11-33.el9_6, 0:23.2.7-6.el9_6

How to fix

Upgrade to a fixed version: Red Hat Enterprise Linux 10 0:24.1.5-6.el10_1, 0:24.1.9-4.el10_2; Red Hat Enterprise Linux 10.0 Extended Update Support 0:24.1.5-6.el10_0; Red Hat Enterprise Linux 6 Extended Lifecycle Support - EXTENSION 0:1.1.0-25.el6_10.16; Red Hat Enterprise Linux 7 Extended Lifecycle Support 0:1.20.4-34.el7_9, 0:1.8.0-36.el7_9.4; Red Hat Enterprise Linux 8 0:1.15.0-9.el8_10, 0:1.20.11-28.el8_10, 0:21.1.3-20.el8_10; Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support 0:1.11.0-8.el8_4.15, 0:1.20.10-4.el8_4; Red Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-On 0:1.11.0-8.el8_4.15, 0:1.20.10-4.el8_4; Red Hat Enterprise Linux 8.6 Advanced Mission Critical Update Support 0:1.12.0-6.el8_6.17, 0:1.20.11-7.el8_6, 0:21.1.3-2.el8_6.6; Red Hat Enterprise Linux 8.6 Extended Update Support Long-Life Add-On 0:1.12.0-6.el8_6.17; Red Hat Enterprise Linux 8.6 Telecommunications Update Service 0:1.20.11-7.el8_6, 0:21.1.3-2.el8_6.6; Red Hat Enterprise Linux 8.6 Update Services for SAP Solutions 0:1.20.11-7.el8_6, 0:21.1.3-2.el8_6.6; Red Hat Enterprise Linux 8.8 Telecommunications Update Service 0:1.12.0-15.el8_8.17, 0:1.20.11-18.el8_8, 0:21.1.3-13.el8_8. Check the vendor advisory for mitigations.

References

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