CVE-2026-55999
Description
A flaw was found in the glamor_font_get() function of the xorg-x11-server. This vulnerability, a heap buffer overflow, occurs when the server processes a specially crafted PCF font file where individual glyph metrics exceed the declared maximum bounds. An authenticated X client can exploit this by loading a malicious font and drawing text, potentially leading to arbitrary code execution with attacker-controlled content and extent. This affects servers utilizing the glamor acceleration backend, such as Xorg with the modesetting driver and Xwayland.
Statement
This Important flaw in xorg-x11-server allows an authenticated X client to achieve arbitrary code execution. By processing a malicious PCF font file where glyph metrics exceed declared bounds, a heap buffer overflow occurs within the glamor acceleration backend. This vulnerability primarily impacts Red Hat systems running Xorg with the modesetting driver or Xwayland, typically found in desktop environments.
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 | 7.5 | 7.8 | 8.5 |
| Attack Vector | Network | Local | Network |
| Attack Complexity | High | Low | High |
| Privileges Required | Low | Low | Low |
| User Interaction | None | None | None |
| Scope | Unchanged | Unchanged | Changed |
| Confidentiality | High | High | High |
| Integrity Impact | High | High | High |
| Availability Impact | High | High | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
NVD: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
cve.org: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H
Understanding the Weakness (CWE)
Integrity,Confidentiality,Availability
Technical Impact: Read Memory; Modify Memory; Execute Unauthorized Code or Commands
Buffer overflows often can be used to execute arbitrary code, which is usually outside the scope of a program's implicit security policy. This can often be used to subvert any other security service.
Availability
Technical Impact: Modify Memory; DoS: Crash, Exit, or Restart; DoS: Resource Consumption (CPU)
Buffer overflows generally lead to crashes. Other attacks leading to lack of availability are possible, including putting the program into an infinite loop.
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