Bug 2541438 (CVE-2026-80431)

Summary: CVE-2026-80431 kitty: out-of-bounds write in the kitty text sizing protocol allows termination of the terminal process
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
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Priority: medium    
Version: unspecifiedKeywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in kitty. This vulnerability allows a program outputting to the terminal to cause a Denial of Service (DoS) by sending a specially crafted Operating System Command (OSC) escape sequence. Due to missing boundary checks when handling text sizing commands with overly long character clusters, an out-of-bounds memory write occurs. This failure results in the termination of the terminal process, closing all active windows, tabs and child processes.
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Bug Depends On: 2542463    
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Description OSIDB Bzimport 2026-09-25 13:48:46 UTC 
Out-of-bounds Write in the natural width branch of the text sizing protocol in kitty from 0.40.0 before 0.49.0 allows a program writing to the terminal to write past the end of a fixed-size buffer, because screen_handle_multicell_command() in kitty/screen.c appends each codepoint of a grapheme cluster with lc.chars[lc.count++] = ch without any capacity check, while lc is declared by the RAII_ListOfChars macro as a four-element char_type array in the function's stack frame, so an OSC 66 escape code whose payload carries a grapheme cluster longer than four codepoints writes beyond that buffer, one 32-bit value per additional codepoint, in the order the codepoints appear. Where the cluster is preceded in the same payload by a sequence that causes an intermediate flush, the buffer is first migrated to the heap by ensure_space_for_chars() and the write occurs past the heap allocation instead. This results in termination of the kitty process and therefore of all its windows, tabs and child processes.