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Advisory severityHigh7.5Red Hat Linux

High [CVE-2026-55999] glamor Font Atlas Heap Buffer Overflow

This high-severity Red Hat Linux advisory covers CVE-2026-55999 affecting Red Hat Enterprise Linux 10.0 Extended Update Support, Red Hat Enterprise Linux 7 Extended Lifecycle Support, Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support.

Aggregated and source-linked by VulniPulse. Data sources, validation and limitations.

CVE-2026-55999 Source published Source updated

VulniPulse record published Record updated

CVE-2026-55999
Affected products & platforms
Red Hat LinuxRed Hat Enterprise Linux
Open source advisory

Summary

Local attackers with a X connection able to provide PCX fonts to the X server xorg-server before 21.2.24 and xwayland before 24.1.13 could cause a heap buffer overflow via SetFont due to missing glyph boundary checks. 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. This Important flaw in xorg-x11-server allows an authenticated X client to achieve arbitrary code execution.

This vulnerability primarily impacts Red Hat systems running Xorg with the modesetting driver or Xwayland, typically found in desktop environments. Red Hat severity: Important — CVSS 7.5 (CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H).

Weakness: CWE-805.

Is CVE-2026-55999 exploited?

No exploitation is reported in the sources VulniPulse tracks: CVE-2026-55999 is not in the CISA KEV catalog (checked ) and this advisory does not report exploitation. That is not proof the vulnerability cannot be exploited.

How do I fix CVE-2026-55999?

Upgrade to a fixed release named by Red Hat:

  • xorg-x11-server-Xwayland-0:24.1.9-4.el10_2.3
  • xorg-x11-server-Xwayland-0:24.1.5-6.el10_0.2
  • xorg-x11-server-0:1.20.4-36.el7_9
  • xorg-x11-server-0:1.20.11-28.el8_10.3
  • xorg-x11-server-Xwayland-0:21.1.3-20.el8_10.3
  • xorg-x11-server-0:1.20.10-5.el8_4.1
  • xorg-x11-server-0:1.20.11-8.el8_6.1
  • xorg-x11-server-Xwayland-0:21.1.3-2.el8_6.8
  • xorg-x11-server-0:1.20.11-19.el8_8.1
  • xorg-x11-server-Xwayland-0:21.1.3-13.el8_8.2
  • xorg-x11-server-0:1.20.11-34.el9_8.3
  • xorg-x11-server-Xwayland-0:24.1.9-4.el9_8.3

24 more fixed releases are listed below.

Confirm against the vendor advisory before you patch.

Affected versions
  • < 21.2.24
  • < 24.1.13

Official advisory · high-confidence parse· fetched 14 days ago·verify at source

Fixed versions
  • xorg-x11-server-Xwayland-0:24.1.9-4.el10_2.3
  • xorg-x11-server-Xwayland-0:24.1.5-6.el10_0.2
  • xorg-x11-server-0:1.20.4-36.el7_9
  • xorg-x11-server-0:1.20.11-28.el8_10.3
  • xorg-x11-server-Xwayland-0:21.1.3-20.el8_10.3
  • xorg-x11-server-0:1.20.10-5.el8_4.1
  • xorg-x11-server-0:1.20.11-8.el8_6.1
  • xorg-x11-server-Xwayland-0:21.1.3-2.el8_6.8
  • xorg-x11-server-0:1.20.11-19.el8_8.1
  • xorg-x11-server-Xwayland-0:21.1.3-13.el8_8.2
  • xorg-x11-server-0:1.20.11-34.el9_8.3
  • xorg-x11-server-Xwayland-0:24.1.9-4.el9_8.3
  • xorg-x11-server-0:1.20.11-21.el9_2.1
  • xorg-x11-server-Xwayland-0:21.1.3-10.el9_2.2
  • xorg-x11-server-0:1.20.11-29.el9_4.1
  • xorg-x11-server-Xwayland-0:22.1.9-8.el9_4.3
  • xorg-x11-server-0:1.20.11-34.el9_6.1
  • xorg-x11-server-Xwayland-0:23.2.7-6.el9_6.3
  • RHSA-2026:38489
  • RHSA-2026:50100
  • RHSA-2026:50117
  • RHSA-2026:38487
  • RHSA-2026:38488
  • RHSA-2026:49606
  • RHSA-2026:49605
  • RHSA-2026:53450
  • RHSA-2026:50116
  • RHSA-2026:52392
  • RHSA-2026:38486
  • RHSA-2026:38490
  • RHSA-2026:49515
  • RHSA-2026:52397
  • RHSA-2026:49516
  • RHSA-2026:52398
  • RHSA-2026:49608
  • RHSA-2026:50718

Official advisory · high-confidence parse· fetched 14 days ago·verify at source

Mitigation

Upgrade to a fixed release: xorg-x11-server-Xwayland-0:24.1.9-4.el10_2.3, xorg-x11-server-Xwayland-0:24.1.5-6.el10_0.2, xorg-x11-server-0:1.20.4-36.el7_9, xorg-x11-server-0:1.20.11-28.el8_10.3, xorg-x11-server-Xwayland-0:21.1.3-20.el8_10.3, xorg-x11-server-0:1.20.10-5.el8_4.1. That is the remediation for this advisory.

The vendor advisory may list interim mitigations or workarounds not captured here. Review it before change work.

Official advisory · high-confidence parse· fetched 14 days ago·verify at source

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