CVE-2026-80431 Out-of-bounds write in the kitty text sizing protocol allows termination of the terminal process
A malicious program can crash the kitty terminal by sending a long grapheme cluster in an OSC 66 escape code, causing an out-of-bounds write.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-80431?
CVE-2026-80431 is a medium-severity memory corruption vulnerability in Kovid Goyal kitty, published on 25 Sep 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Official description
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.
Weakness: CWE-787
Which versions are affected by CVE-2026-80431?
How do I fix CVE-2026-80431?
No fix has been published for CVE-2026-80431 yet. Limit exposure of the affected software until one is available.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-80431 being exploited?
There is no known exploitation of CVE-2026-80431 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-80431, GHSA-fx7r-q727-j825, UBUNTU-CVE-2026-80431.