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Vulnerability record · CVE-2026-55999 · published 8 July 2026

CVE-2026-55999: X.org x server heap-based buffer overflow vulnerability

XX.Org · X Server

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.

7.8 CVSS 3.1 High EPSS 0.33% · top 76.0% CWE-122 · Heap-based buffer overflow
7.8CVSS 3.1 base score
0.33%EPSS exploitation probability, 30 days
NoNot in CISA KEV
2Affected product versions listed by NVD
2References
9 Jul 2026Last modified by NVD

Description

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.

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Affected products

2 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://gitlab.freedesktop.org/xorg/xserver/-/commit/fbf7bac22e2c6bd627fb042742a23318263edae1 Patch
https://www.openwall.com/lists/oss-security/2026/07/08/2 Mailing ListPatchThird Party Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

9.8CVE-2023-6816X.org x server out-of-bounds write vulnerabilityA flaw was found in X.Org server. Both DeviceFocusEvent and the XIQueryPointer reply contain a bit for each logical button currently down. Buttons ca…EPSS 2.1%9.8CVE-2017-12176Debian linux improper input validation vulnerabilityxorg-x11-server before 1.19.5 was missing extra length validation in ProcEstablishConnection function allowing malicious X client to cause X server t…EPSS 4.2%9.8CVE-2017-12177Debian linux integer overflow vulnerabilityxorg-x11-server before 1.19.5 was vulnerable to integer overflow in ProcDbeGetVisualInfo function allowing malicious X client to cause X server to cr…EPSS 4.4%9.8CVE-2017-12178Debian linux improper input validation vulnerabilityxorg-x11-server before 1.19.5 had wrong extra length check in ProcXIChangeHierarchy function allowing malicious X client to cause X server to crash o…EPSS 4.2%9.8CVE-2017-12179Debian linux integer overflow vulnerabilityxorg-x11-server before 1.19.5 was vulnerable to integer overflow in (S)ProcXIBarrierReleasePointer functions allowing malicious X client to cause X s…EPSS 4.4%9.8CVE-2017-12180Debian linux improper input validation vulnerabilityxorg-x11-server before 1.19.5 was missing length validation in XFree86 VidModeExtension allowing malicious X client to cause X server to crash or pos…EPSS 4.2%9.8CVE-2017-12181Debian linux improper input validation vulnerabilityxorg-x11-server before 1.19.5 was missing length validation in XFree86 DGA extension allowing malicious X client to cause X server to crash or possib…EPSS 4.2%9.8CVE-2017-12182Debian linux improper input validation vulnerabilityxorg-x11-server before 1.19.5 was missing length validation in XFree86 DRI extension allowing malicious X client to cause X server to crash or possib…EPSS 4.2%

Source: NIST National Vulnerability Database (record CVE-2026-55999), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.