Bug 2547409 (CVE-2026-107168)

Summary: CVE-2026-107168 m17n-lib: Parser infinite loop on malformed UTF-8 in count_utf_8_chars()
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in m17n-lib. By providing crafted input containing an invalid UTF-8 character sequence, an attacker can cause the text parsing function to enter an infinite loop. This issue leads to sustained high CPU utilization, resulting in a Denial of Service (DoS) for the affected application.
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Bug Depends On: 2547603    
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Description OSIDB Bzimport 2026-10-07 12:01:20 UTC 
A flaw was found in m17n-lib. An invalid UTF-8 sequence containing a lead byte in the 0xFE-0xFF range can cause count_utf_8_chars() (src/mtext.c) to make no parsing progress, resulting in an infinite loop and sustained CPU consumption when processing crafted M-text input. Independently reproduced: a crafted .mim database entry containing byte 0xFF causes the plain build to spin at ~100% CPU until killed (confirmed via `time`: ~4.9s of CPU time consumed in a 5s window, process required external termination). Root cause confirmed in src/mtext.c: CHAR_UNITS_BY_HEAD_UTF8(0xFF) returns 0, so the scanning pointer in count_utf_8_chars() never advances. Upstream maintainer Kenichi Handa reviewed the report and confirmed the affected byte range is 0xFE-0xFF rather than the broader 0xFC-0xFF range originally suggested by the reporter.