CVE-2026-34000
Description
A flaw was found in the X.Org X server. This out-of-bounds read vulnerability in the XKB geometry processing, specifically within the CheckSetGeom() and XkbAddGeomKeyAlias functions, allows an attacker to read uninitialized or out-of-bounds memory. An attacker with a connection to the X11 server, either locally or remotely, can exploit this without user interaction. This could lead to the disclosure of memory contents or cause a denial of service by crashing the server.
Statement
This out-of-bounds read vulnerability in the X.Org X server's XKB geometry processing could allow an attacker to leak memory contents or cause a denial of service. Exploitation requires an attacker to establish a connection to the X11 server, either locally or through forwarded remote sessions. Red Hat Enterprise Linux systems with a graphical environment enabled are potentially affected.
Mitigation
To mitigate this vulnerability, restrict access to the X11 server. On systems where a graphical environment is not required, consider disabling the X server entirely by setting the default system target to multi-user mode. For systems requiring the X server, ensure that X11 forwarding is disabled in SSH configurations if not explicitly needed, and restrict direct X11 connections to trusted users and networks through firewall rules. If changes are made to SSH configuration, the `sshd` service must be restarted. If the default system target is changed, a system reboot is required.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 6.1 | 9.1 | 6.1 |
| Attack Vector | Local | Network | Local |
| Attack Complexity | Low | Low | Low |
| Privileges Required | Low | None | Low |
| User Interaction | None | None | None |
| Scope | Unchanged | Unchanged | Unchanged |
| Confidentiality | High | High | High |
| Integrity Impact | None | None | None |
| Availability Impact | Low | High | Low |
Vector
Red Hat: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:L
NVD: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
cve.org: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:L
Understanding the Weakness (CWE)
Confidentiality
Technical Impact: Read Memory
An attacker could get secret values such as cryptographic keys, PII, memory addresses, or other information that could be used in additional attacks.
Confidentiality
Technical Impact: Bypass Protection Mechanism
Out-of-bounds memory could contain memory addresses or other information that can be used to bypass ASLR and other protection mechanisms in order to improve the reliability of exploiting a separate weakness for code execution.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
An attacker could cause a segmentation fault or crash by causing memory to be read outside of the bounds of the buffer. This is especially likely when the code reads a variable amount of data and assumes that a sentinel exists to stop the read operation, such as a NUL in a string.
Other
Technical Impact: Varies by Context
The read operation could produce other undefined or unexpected results.
Acknowledgements
Red Hat would like to thank Jan-Niklas Sohn (TrendAI Zero Day Initiative) for reporting this issue.
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