Description
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.
Published: 2026-09-10
Score: 9.2 Critical
EPSS: n/a
KEV: No
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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

Subscriptions

Libxfont2 Libxfont2
cve-icon MITRE

Status: PUBLISHED

Assigner: suse

Published:

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

cve-icon OpenCVE Enrichment

Updated: 2026-08-07T09:58:19Z

Weaknesses