CVE-2026-59679: libXfont2 Out-of-Bounds Read/Write via Mismatched Glyph Counts

This advisory describes CVE-2026-59679: a critical (CVSS 3.1 9.0 / CVSS 4.0 9.2) out-of-bounds read/write vulnerability in libXfont2's fs_read_glyphs() caused by mismatched reply sizes from the X font-server protocol; a malicious or MITM font server can trigger heap corruption, information disclosure, denial-of-service, or potentially remote code execution. The report details root cause, affected versions (<= 2.0.8), an upstream fix in 2.0.9, exploitation steps, detection indicators (crashes, connections to port 7100), and immediate mitigations including upgrading to 2.0.9 and blocking/disabling remote font-server usage.