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Integer Overflow Leading to Heap Buffer Overflow in libXfont2 BitmapScaleBitmaps
CVE-2026-56001 is an integer overflow leading to a heap buffer overflow in BitmapScaleBitmaps() in libXfont2 versions before 2.0.8. A 32-bit variable stores the allocation size for scaled glyph bitmaps. Excessive per-glyph byte counts can overflow this variable, causing calloc() to allocate an undersized buffer that subsequent bitmap operations overwrite. An attacker can trigger the flaw by loading a crafted PCF font with a scale factor that inflates glyph byte counts, potentially executing arbitrary code within the X server.
What it means and what to do now: patch path, interim mitigations, and the assume-compromise checklist.
What an attacker gets, and what they’ve been doing with it.
Successful exploitation can compromise the confidentiality, integrity, and availability of the X server through arbitrary code execution in its process context. Heap corruption can also disrupt the server. The privileges available to attacker-controlled code depend on those of the affected X server process.
If you can’t patch tonight, do this now.
No vulnerability-specific workaround or temporary mitigation is documented.
Patch, then assume compromise.
Upgrade libXfont2 to version 2.0.8 or later, or install the distribution's backported security update. For Debian stable (trixie), upgrade libxfont packages to version 1:2.0.6-1+deb13u1 or later.
No public exploits tracked yet. Mallory keeps watching.
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
28 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.