fs_read_glyphs() in the libXfont2 font-server client (src/fc/fserve.c) indexes the per-character encoding[] array using num_chars from the FS_QueryXBitmaps16 reply, but that array was allocated with a size derived from num_extents in the separate FS_QueryXExtents16 reply. The two CARD32 fields are never cross-checked. A malicious or compromised font server can send a small num_extents (e.g. 1) in the extents reply, then a large num_chars (e.g. 100000) in the bitmaps reply. This causes attacker-controlled out-of-bounds heap read and writes.

Metrics

Attack Vector Network

Attack Complexity High

Privileges Required None

Attack Requirements None

User Interaction None

Vulnerable System Confidentiality Impact High

Vulnerable System Integrity Impact High

Vulnerable System Availability Impact High

Subsequent System Confidentiality Impact None

Subsequent System Integrity Impact None

Subsequent System Availability Impact None

Attack Vector Network

Attack Complexity High

Privileges Required None

Scope Changed

Confidentiality Impact High

Integrity Impact High

Availability Impact High

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

Key SSVC decision points have not yet been added.

Affected Vendors & Products

Vendors Products
Libxfont2
  • Libxfont2

No data.

No data.

References
Link Providers
https://bugzilla.suse.com/show_bug.cgi?id=CVE-2026-59679 cve-icon cve-icon
https://nvd.nist.gov/vuln/detail/CVE-2026-59679 cve-icon
https://www.cve.org/CVERecord?id=CVE-2026-59679 cve-icon
History

Thu, 10 Sep 2026 08:30:00 +0000

Type Values Removed Values Added
Description A flaw was found in the libXfont2 font-server client. A remote attacker, by operating a malicious font server, could exploit an out-of-bounds read/write vulnerability. This occurs because the client incorrectly handles font data, leading to an out-of-bounds memory access. This can lead to privilege escalation if the X server runs with root privileges, or a denial of service (crash) if it runs as an unprivileged user. fs_read_glyphs() in the libXfont2 font-server client (src/fc/fserve.c) indexes the per-character encoding[] array using num_chars from the FS_QueryXBitmaps16 reply, but that array was allocated with a size derived from num_extents in the separate FS_QueryXExtents16 reply. The two CARD32 fields are never cross-checked. A malicious or compromised font server can send a small num_extents (e.g. 1) in the extents reply, then a large num_chars (e.g. 100000) in the bitmaps reply. This causes attacker-controlled out-of-bounds heap read and writes.
Title libxfont2: Font Server Client encoding[] Out-Of-Bounds Read/Write fs_read_glyphs() heap OOB read/write via encoding array index mismatch in libXfont2
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H'}

 cvssV4_0

{'score': 9.2, 'vector': 'CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N'}

cvssV3_1

{'score': 9, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H'}

Fri, 07 Aug 2026 10:30:00 +0000

Type Values Removed Values Added
First Time appeared Libxfont2
Libxfont2 libxfont2
Vendors & Products Libxfont2
Libxfont2 libxfont2

Thu, 06 Aug 2026 13:45:00 +0000

Type Values Removed Values Added
Weaknesses CWE-119
CWE-787

Thu, 06 Aug 2026 12:15:00 +0000

Type Values Removed Values Added
Description A flaw was found in the libXfont2 font-server client. A remote attacker, by operating a malicious font server, could exploit an out-of-bounds read/write vulnerability. This occurs because the client incorrectly handles font data, leading to an out-of-bounds memory access. This can lead to privilege escalation if the X server runs with root privileges, or a denial of service (crash) if it runs as an unprivileged user.
Title libxfont2: Font Server Client encoding[] Out-Of-Bounds Read/Write
References
Metrics threat_severity

None

 cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H'}

threat_severity

Important
cve-icon MITRE

Status: PUBLISHED

Assigner: suse

Published: 2026-09-10T08:15:24.892Z

Updated: 2026-09-10T08:15:24.892Z

Reserved: 2026-07-06T11:59:28.119Z

Link: CVE-2026-59679

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-09-10T09:17:02.883

Modified: 2026-09-10T09:17:02.883

Link: CVE-2026-59679

cve-icon Redhat

Severity : Important

Publid Date: 2026-08-05T10:00:00Z

Links: CVE-2026-59679 - Bugzilla