CVE-2026-44950: fs_read_glyphs() heap buffer overflow via cumulative glyph data overflow in libXfont2

Severity: critical (CVSS 9.0 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-09-10 · updated 2026-09-10
Weakness: CWE-122

Description

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 products

libXfont: from ? through 2.0.8
SUSE Container suse/kiosk/tigervnc-x11vnc:1.14-63.8: from ? before 2.0.3-150000.3.6.1 — fixed in 2.0.3-150000.3.6.1
SUSE Container suse/kiosk/xorg:21.1-83.7: from ? before 2.0.3-150000.3.6.1 — fixed in 2.0.3-150000.3.6.1
SUSE Image SLES-SAP-Azure: from ? before 2.0.7-160000.5.1 — fixed in 2.0.7-160000.5.1
SUSE Image SLES-SAP-Azure-3P: from ? before 2.0.7-160000.5.1 — fixed in 2.0.7-160000.5.1
SUSE Image SLES-SAP-BYOS-Azure: from ? before 2.0.7-160000.5.1 — fixed in 2.0.7-160000.5.1
SUSE Image SLES-SAP-BYOS-EC2: from ? before 2.0.7-160000.5.1 — fixed in 2.0.7-160000.5.1
SUSE Image SLES-SAP-BYOS-GCE: from ? before 2.0.7-160000.5.1 — fixed in 2.0.7-160000.5.1
SUSE Image SLES-SAP-GCE: from ? before 2.0.7-160000.5.1 — fixed in 2.0.7-160000.5.1
SUSE Image SLES-SAP-GCE-3P: from ? before 2.0.7-160000.5.1 — fixed in 2.0.7-160000.5.1
SUSE Image SLES-SAPCAL-GCE: from ? before 2.0.7-160000.5.1 — fixed in 2.0.7-160000.5.1
SUSE Image SLES12-SP5-Azure-SAP-BYOS: from ? before 2.0.3-3.6.1 — fixed in 2.0.3-3.6.1
SUSE Image SLES12-SP5-Azure-SAP-On-Demand: from ? before 2.0.3-3.6.1 — fixed in 2.0.3-3.6.1
SUSE Image SLES12-SP5-EC2-SAP-BYOS: from ? before 2.0.3-3.6.1 — fixed in 2.0.3-3.6.1
SUSE Image SLES12-SP5-EC2-SAP-On-Demand: from ? before 2.0.3-3.6.1 — fixed in 2.0.3-3.6.1
SUSE Image SLES12-SP5-GCE-SAP-BYOS: from ? before 2.0.3-3.6.1 — fixed in 2.0.3-3.6.1
SUSE Image SLES12-SP5-GCE-SAP-On-Demand: from ? before 2.0.3-3.6.1 — fixed in 2.0.3-3.6.1
SUSE Image SLES15-SP6-SAP: from ? before 2.0.3-150000.3.6.1 — fixed in 2.0.3-150000.3.6.1
SUSE Image SLES15-SP6-SAP-Azure: from ? before 2.0.3-150000.3.6.1 — fixed in 2.0.3-150000.3.6.1
SUSE Image SLES15-SP6-SAP-Azure-3P: from ? before 2.0.3-150000.3.6.1 — fixed in 2.0.3-150000.3.6.1
SUSE Image SLES15-SP6-SAP-BYOS: from ? before 2.0.3-150000.3.6.1 — fixed in 2.0.3-150000.3.6.1
SUSE Image SLES15-SP6-SAP-BYOS-Azure: from ? before 2.0.3-150000.3.6.1 — fixed in 2.0.3-150000.3.6.1
SUSE Image SLES15-SP6-SAP-BYOS-EC2: from ? before 2.0.3-150000.3.6.1 — fixed in 2.0.3-150000.3.6.1
SUSE Image SLES15-SP6-SAP-BYOS-GCE: from ? before 2.0.3-150000.3.6.1 — fixed in 2.0.3-150000.3.6.1
SUSE Image SLES15-SP6-SAP-EC2: from ? before 2.0.3-150000.3.6.1 — fixed in 2.0.3-150000.3.6.1
SUSE Image SLES15-SP6-SAP-GCE: from ? before 2.0.3-150000.3.6.1 — fixed in 2.0.3-150000.3.6.1
SUSE Image SLES15-SP6-SAP-Hardened: from ? before 2.0.3-150000.3.6.1 — fixed in 2.0.3-150000.3.6.1
SUSE Image SLES15-SP6-SAP-Hardened-Azure: from ? before 2.0.3-150000.3.6.1 — fixed in 2.0.3-150000.3.6.1
SUSE Image SLES15-SP6-SAP-Hardened-BYOS: from ? before 2.0.3-150000.3.6.1 — fixed in 2.0.3-150000.3.6.1
SUSE Image SLES15-SP6-SAP-Hardened-BYOS-Azure: from ? before 2.0.3-150000.3.6.1 — fixed in 2.0.3-150000.3.6.1

How to fix

Upgrade to a fixed version: SUSE Container suse/kiosk/tigervnc-x11vnc:1.14-63.8 2.0.3-150000.3.6.1; SUSE Container suse/kiosk/xorg:21.1-83.7 2.0.3-150000.3.6.1; SUSE Image SLES-SAP-Azure 2.0.7-160000.5.1; SUSE Image SLES-SAP-Azure-3P 2.0.7-160000.5.1; SUSE Image SLES-SAP-BYOS-Azure 2.0.7-160000.5.1; SUSE Image SLES-SAP-BYOS-EC2 2.0.7-160000.5.1; SUSE Image SLES-SAP-BYOS-GCE 2.0.7-160000.5.1; SUSE Image SLES-SAP-GCE 2.0.7-160000.5.1; SUSE Image SLES-SAP-GCE-3P 2.0.7-160000.5.1; SUSE Image SLES-SAPCAL-GCE 2.0.7-160000.5.1; SUSE Image SLES12-SP5-Azure-SAP-BYOS 2.0.3-3.6.1; SUSE Image SLES12-SP5-Azure-SAP-On-Demand 2.0.3-3.6.1. Check the vendor advisory for mitigations.

References

https://bugzilla.suse.com/show_bug.cgi?id=CVE-2026-44950

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