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 a malicious user or application to execute unauthorized code on the system. This could lead to a complete takeover of the X server, potentially exposing user data or allowing an attacker to monitor user activity.
Technical details
A heap-based buffer overflow exists in libXfont2's pcfReadFont() function due to insufficient validation of PCF font files. The library allocates a bitmap buffer based on the 'bitmapSizes' value provided in the file but performs subsequent writes based on per-glyph metrics without verifying they fit within the allocated space. An attacker authenticated as an X client can provide a malicious PCF font with mismatched metrics to trigger the overflow during font parsing. This can result in arbitrary code execution within the context of the X server. The issue is addressed in version 2.0.8 by validating bitmap sizes, offsets, and glyph extents against the actual buffer capacity.
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: CVE published to NVD.