CVE-2026-50256
Stack-Based Buffer Overflow in X.Org X Server
Publication date: 2026-06-05
Last updated on: 2026-06-05
Assigner: Red Hat, Inc.
Description
Description
CVSS Scores
EPSS Scores
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Meta Information
Affected Vendors & Products
| Vendor | Product | Version / Range |
|---|---|---|
| the_x.org_foundation | xorg_x11_server | to 21.1.22 (inc) |
| the_x.org_foundation | xorg_x11_server_xwayland | to 24.1.9 (inc) |
Helpful Resources
Exploitability
| CWE ID | Description |
|---|---|
| CWE-121 | A stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function). |
Attack-Flow Graph
AI Powered Q&A
Can you explain this vulnerability to me?
CVE-2026-50256 is a stack-based buffer overflow vulnerability in the X.Org X server and Xwayland. It occurs because the X server allocates a 256-byte stack buffer for font alias names, but the libXfont2 library allows font alias names up to 1024 bytes. When a font alias name between 257 and 1023 bytes is processed, the X server copies it into the smaller buffer without checking its length, causing a buffer overflow.
This mismatch in handling font name lengths can lead to memory corruption, which may be exploited to crash the server or escalate privileges if the X server is running with root permissions.
How can this vulnerability impact me? :
This vulnerability can be exploited by any X client connected to the X server to cause a denial of service by crashing the server.
More seriously, if the X server is running with root privileges, an attacker could exploit this buffer overflow to escalate their privileges, potentially gaining unauthorized root access to the system.
How can this vulnerability be detected on my network or system? Can you suggest some commands?
This vulnerability can be detected by checking the versions of the xorg-x11-server and xorg-x11-server-Xwayland packages installed on your system, as vulnerable versions are up to 21.1.22 for xorg-x11-server and up to 24.1.9 for xorg-x11-server-Xwayland.
You can use package management commands to verify the installed versions. For example, on a Red Hat-based system, you can run:
- rpm -q xorg-x11-server
- rpm -q xorg-x11-server-Xwayland
If the versions are at or below the vulnerable versions, your system is susceptible to this vulnerability.
Additionally, monitoring for crashes or abnormal behavior of the X server when processing font alias names could indicate exploitation attempts, but no specific detection commands or signatures are provided.
What immediate steps should I take to mitigate this vulnerability?
The immediate mitigation step is to update the xorg-x11-server and xorg-x11-server-Xwayland packages to fixed versions where the vulnerability is resolved.
- Upgrade xorg-x11-server to version 21.1.23 or later.
- Upgrade xorg-x11-server-Xwayland to version 24.1.12 or later.
If updating is not immediately possible, consider restricting access to the X server to trusted clients only, as any connected X client can exploit this vulnerability.
Also, monitor for any unusual crashes or behavior of the X server and apply any vendor-provided patches as soon as they become available.