CVE-2026-59679: LIBXFONT2

Critical severity, CVSS 9.0. EPSS: 0.4% chance of exploitation in the next 30 days.

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.

Affected products

• LIBXFONT2 LIBXFONT2
• Suse Container Suse/kiosk/tigervnc-x11vnc:1.14-63.8
• Suse Container suse/kiosk/xorg:21.1-83.7
• Suse Image Sles-SAP-Azure
• Suse Image Sles-SAP-Azure-3p
• Suse Image Sles-SAP-Byos-Azure
• Suse Image Sles-SAP-Byos-EC2
• Suse Image Sles-SAP-Byos-Gce
• Suse Image Sles-SAP-Gce
• Suse Image Sles-SAP-Gce-3p
• Suse Image Sles-Sapcal-Gce
• Suse Image SLES12-SP5-Azure-SAP-Byos
• Suse Image SLES12-SP5-Azure-SAP-On-Demand
• Suse Image SLES12-SP5-EC2-SAP-Byos
• Suse Image SLES12-SP5-EC2-SAP-On-Demand
• Suse Image SLES12-SP5-Gce-SAP-Byos
• Suse Image SLES12-SP5-Gce-SAP-On-Demand
• Suse Image SLES15-SP6-SAP
• Suse Image SLES15-SP6-SAP-Azure
• Suse Image SLES15-SP6-SAP-Azure-3p
• Suse Image SLES15-SP6-SAP-Byos
• Suse Image SLES15-SP6-SAP-Byos-Azure
• Suse Image SLES15-SP6-SAP-Byos-EC2
• Suse Image SLES15-SP6-SAP-Byos-Gce
• Suse Image SLES15-SP6-SAP-EC2
• and 55 more

Published 2026-09-10. Last modified 2026-09-10.