Bug 2496640 (CVE-2026-56001)

Summary: CVE-2026-56001 libXfont2: BitmapScaleBitmaps Integer Overflow Heap Buffer Overflow
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: high Docs Contact:
Priority: high    
Version: unspecifiedCC: gtanzill, jbuscemi, rhel-process-autobot, security-response-team, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in libXfont2. In the BitmapScaleBitmaps() function, an integer overflow can occur when calculating the memory needed for font glyphs. This overflow leads to a heap buffer overflow, where a smaller-than-required memory buffer is allocated. A local attacker can exploit this by loading a specially crafted PCF font, potentially leading to arbitrary code execution or a denial of service.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Deadline: 2026-07-08   

Description OSIDB Bzimport 2026-07-02 18:31:34 UTC 
In libXfont2's BitmapScaleBitmaps() function, a 32-bit variable keeps the number of bytes to allocate. If the value overflows due to excessive per-glyph byte counts, the resulting calloc() allocates a buffer too small for the subsequent operations. An attacker can trigger this by loading a crafted PCF font via SetFontPath + OpenFont at a scale factor that inflates per-glyph byte counts.