CVE-2026-44950

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

This page contains facts from public vulnerability sources. Check the original advisory before updating.

This page shows selected source facts. See the linked advisories for the complete description and affected versions.

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.

CVSS 9.5 · Critical · EPSS 0.3% · Fix available

Published

2026-09-10T08:19:55.462Z

Updated

2026-09-10T18:26:50.408Z

Stack: system

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