CVE-2026-44950 fs_read_glyphs() heap buffer overflow via cumulative glyph data overflow in libXfont2
A malicious font server can trigger a heap buffer overflow in libXfont2 via cumulative glyph data, potentially allowing arbitrary code execution.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-44950?
CVE-2026-44950 is a critical memory corruption vulnerability in Container suse/kiosk/tigervnc-x11vnc:1.14-63.8, published on 10 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-122
Which versions are affected by CVE-2026-44950?
How do I fix CVE-2026-44950?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-44950 being exploited?
There is no known exploitation of CVE-2026-44950 in the wild and no public exploit code.
Sources
Also known as AZL-101733, DEBIAN-CVE-2026-44950, GHSA-72vv-3gwg-8289, UBUNTU-CVE-2026-44950.