Bug 2547603

Summary: CVE-2026-107168 m17n-lib: Parser infinite loop on malformed UTF-8 in count_utf_8_chars() [fedora-all]
Product: [Fedora] Fedora Reporter: Vladimir Vasilev <vvasilev>
Component: m17n-libAssignee: Mike FABIAN <mfabian>
Status: NEW --- QA Contact: Fedora Extras Quality Assurance <extras-qa>
Severity: medium Docs Contact:
Priority: medium    
Version: rawhideCC: i18n-bugs, mfabian, petersen, pnemade
Target Milestone: ---Keywords: Security, SecurityTracking
Target Release: ---   
Hardware: Unspecified   
OS: Unspecified   
Whiteboard: {"flaws": ["73f5d9fb-7b70-4e69-a4b4-3d4362c1b857"]}
Fixed In Version: Doc Type: ---
Doc Text:
Story Points: ---
Clone Of: Environment:
Last Closed: Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On:    
Bug Blocks: 2547409    

Description Vladimir Vasilev 2026-10-07 17:48:21 UTC 
Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.

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.