CVE-2026-59679 fs_read_glyphs() heap OOB read/write via encoding array index mismatch in libXfont2
A malicious font server can trigger heap out-of-bounds read and write in libXfont2, potentially leading to code execution or denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-59679?
CVE-2026-59679 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) 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.
Weakness: CWE-787
Which versions are affected by CVE-2026-59679?
How do I fix CVE-2026-59679?
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-2026-59679 being exploited?
There is no known exploitation of CVE-2026-59679 in the wild and no public exploit code.
Sources
Also known as AZL-101730, DEBIAN-CVE-2026-59679, GHSA-g44m-wpf7-gr7x, UBUNTU-CVE-2026-59679.