Bug 2564117 (CVE-2026-61627)

Summary: CVE-2026-61627 libass: libass: Arbitrary code execution via crafted subtitle files
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
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Priority: high    
Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in libass. An attacker could exploit this vulnerability by enticing a user to process a specially crafted subtitle file, triggering an out-of-bounds write during line measurement. Successful exploitation may result in arbitrary code execution or cause an application crash leading to a Denial of Service (DoS).
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Bug Depends On: 2565474, 2565475, 2565477, 2565479, 2565481, 2565483    
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Description OSIDB Bzimport 2026-10-30 15:07:23 UTC 
libass is a portable subtitle renderer for the `ASS`/SSA (Advanced Substation Alpha/Substation Alpha) subtitle format. Prior to 0.17.5, libass can overread and overwrite the glyph array in `wrap_lines_measure` while rendering malicious `ASS` content. In `wrap modes other than two`, a final line ending with a literal backslash-n sequence and otherwise consisting only of such sequences or spaces can remain after early trimming and make the line-measurement loops overshoot by one glyph. When the total text size exactly matches the allocated glyph-array capacity, the first loop reads an uninitialized 32-bit fixed-point `pos.x` value, although that value is not subsequently used. The second loop writes `pos.x` and `pos.y` beyond the array, zeroing the first and adding an attacker-controllable offset to the second. No actual exploitation beyond possible denial of service is known; broader exploitation is theoretical and constrained by the addresses, limited writes, and ASLR. This issue is fixed in version 0.17.5.