Affected: AlmaLinux:8: libXfont2, AlmaLinux:8: libXfont2-devel

X.Org X11 libXfont2 runtime library

Security Fix(es):

* libxfont2: Font Server Client encoding[] Out-Of-Bounds Read/Write (CVE-2026-59679) * libxfonts2: libXfont2: Privilege Escalation via Heap Buffer Overflow in Font Server Client (CVE-2026-44950)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

fs_read_glyphs() in the libXfont2 font-server client (src/fc/fserve.c) copies each glyph's bitmap into a single buffer. Existing checks validates only that the source slice (position, length) lies within the source bitmap buffer. It does not check whether the running destination cursor has exceeded the allocation.

A malicious font server can send overlapping source offsets -- for example 1000 glyphs each referencing {position:0, length:64} with nbytes=64. Each individual source range passes the existing validation, but the cumulative writes total 64000 bytes into a 64-byte destination buffer. This is a heap buffer overflow with attacker-controlled content.

fs_read_glyphs() in the libXfont2 font-server client (src/fc/fserve.c) copies each glyph's bitmap into a single buffer. Existing checks validates only that the source slice (position, length) lies within the source bitmap buffer. It does not check whether the running destination cursor has exceeded the allocation.

A malicious font server can send overlapping source offsets -- for example 1000 glyphs each referencing {position:0, length:64} with nbytes=64. Each individual source range passes the existing validation, but the cumulative writes total 64000 bytes into a 64-byte destination buffer. This is a heap buffer overflow with attacker-controlled content.

Affected: openEuler:22.03-LTS-SP4: libXfont2, openEuler:24.03-LTS-SP1: libXfont2, openEuler:24.03-LTS-SP3: libXfont2, openEuler:24.03-LTS-SP4: libXfont2, openEuler:20.03-LTS-SP4: libXfont2

libXfont provides the core of the legacy X11 font system, handling the index files (fonts.dir, fonts.alias, fonts.scale), the various font file formats, and rasterizing them. contains runtime library. Security Fix(es):

A flaw was found in the libXfont2 font-server client. This heap buffer overflow vulnerability allows a malicious font server to send specially crafted glyph data. The fs_read_glyphs() function fails to properly validate the total size of the incoming data, leading to an overwrite of memory beyond the intended buffer. If the X server runs as a privileged user, this could result in privilege escalation, allowing an attacker to gain higher access. If the X server runs as an unprivileged user, it could lead to a denial of service, causing the system to crash.(CVE-2026-44950)

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.(CVE-2026-59679)

libXfont2-2-2.0.7-3.1 on GA media

libxfonts2: libXfont2: Privilege Escalation via Heap Buffer Overflow in Font Server Client libxfont2: Font Server Client encoding[] Out-Of-Bounds Read/Write

Affected: Rocky Linux:8: libXfont2

X.Org X11 libXfont2 runtime library

Security Fix(es):

* libxfont2: Font Server Client encoding[] Out-Of-Bounds Read/Write (CVE-2026-59679)

* libxfonts2: libXfont2: Privilege Escalation via Heap Buffer Overflow in Font Server Client (CVE-2026-44950)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

Security update for libXfont2

Affected: Ubuntu:16.04:LTS: libxfont2

fs_read_glyphs() in the libXfont2 font-server client (src/fc/fserve.c) copies each glyph's bitmap into a single buffer. Existing checks validates only that the source slice (position, length) lies within the source bitmap buffer. It does not check whether the running destination cursor has exceeded the allocation. A malicious font server can send overlapping source offsets -- for example 1000 glyphs each referencing {position:0, length:64} with nbytes=64. Each individual source range passes the existing validation, but the cumulative writes total 64000 bytes into a 64-byte destination buffer. This is a heap buffer overflow with attacker-controlled content.

Ein entfernter, anonymer Angreifer kann mehrere Schwachstellen in X.Org X11 ausnutzen, um seine Privilegien zu erhöhen, und um einen Denial of Service Angriff durchzuführen.