Executive brief
libXfont2 is a core library used by the X Window System to handle and display fonts. A vulnerability in how this library processes font files allows an attacker to crash the display server or potentially execute malicious code. This could lead to a full system compromise or a disruption of graphical services on affected Linux and Unix-like systems.
Technical details
A heap buffer overflow exists in the ComputeScaledProperties() function of libXfont2 when parsing Portable Compiled Format (PCF) files. The function allocates a fixed-size buffer of 70 slots for font properties, but the computeProps() helper fails to perform bounds checking when writing to this buffer. An attacker can provide a malicious font containing numerous duplicate properties that match entries in the fontPropTable, causing the library to write past the end of the allocated 1120-byte buffer. This can be triggered by an authenticated X client using SetFontPath and OpenFont requests. The issue is resolved in version 2.0.8 by implementing proper capacity checks during property iteration.
Affected products
- X.Org libXfont2 before 2.0.8
Timeline
- 2026-06-01: patched: Fix committed to GitLab repository
- 2026-07-08: advisory: X.Org Security Advisory released
- 2026-07-08: disclosed: Public disclosure on oss-security mailing list