{"id":"CVE-2026-80431","title":"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…","summary":"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…","severity":"medium","cvss":6.8,"cvssVector":"CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N","cwe":["CWE-787"],"vendor":"Kovid Goyal","product":"kitty","affected":["kitty >= 0.40.0 < 0.49.0"],"published":"2026-09-25","updated":"2026-09-25","sourceUpdated":"2026-09-25T16:17:27.880","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-80431","references":[{"url":"https://github.com/kovidgoyal/kitty/commit/7d2fbaadcc2b1eeeef89bd875ec622b42362574b","label":"4daa8cea-433a-44bd-9456-53b127fc289a"},{"url":"https://github.com/kovidgoyal/kitty/releases/tag/v0.49.0","label":"4daa8cea-433a-44bd-9456-53b127fc289a"},{"url":"https://secur0.com/en/cna/cve-list/cve-2026-80431-kitty-text-sizing-out-of-bounds-write","label":"4daa8cea-433a-44bd-9456-53b127fc289a"},{"url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-80431.json"},{"url":"https://access.redhat.com/security/cve/CVE-2026-80431"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-80431"}],"tags":["nvd","cve.org","csaf","vex","red-hat"],"ssvc":{"exploitation":"none","automatable":"no","technicalImpact":"partial","timestamp":"2026-09-25T15:05:06.462333Z"},"cvssSource":"cna","ingestedAt":"2026-09-25T14:09:46.372Z","scores":{"cna":6.8,"vendor":5.5},"slug":"CVE-2026-80431","body":"## Overview\n\nOut-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.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.\n\n## Vendor advisories\n\n- **Red Hat VEX** · updated 2026-09-25 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-80431.json)","depth":"sunlit","depthScore":37,"depthScoreParts":{"impact":37.4,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}