Bug 2496641 (CVE-2026-56002)

Summary: CVE-2026-56002 libXfont2: PCF Font Parsing 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. A specially crafted PCF (Portable Compiled Format) font file, when processed by libXfont2, can lead to a buffer overflow. This occurs because the font parsing process does not properly validate the size of a bitmap buffer against the glyph metrics provided in the malicious font file. An attacker could exploit this vulnerability by providing a malicious 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:
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Deadline: 2026-07-08   

Description OSIDB Bzimport 2026-07-02 18:36:08 UTC 
In libXfont2's pcfReadFont() function, the repadded bitmap buffer is allocated using a bitmapSizes[] value read directly from the PCF file without cross-validation against per-glyph metrics. Writing to that array uses the per-glyph metrics from the file also without validation. A malicious PCF font can declare a tiny bitmapSizes[] value (e.g. 16 bytes) for the server's glyph pad index and a per-glyph metrics that exceeds this size, causing a write past the end of the allocation with attacker-controlled content from the PCF BITMAPS payload. No rendering is needed -- the overflow occurs during font parsing itself.