# 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.

- **Severity:** Medium 6.8 (`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`)
- **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 available:** No
- **Published:** 25 Sep 2026
- **Updated:** 25 Sep 2026
- **Also known as:** DEBIAN-CVE-2026-80431, GHSA-fx7r-q727-j825, UBUNTU-CVE-2026-80431

## 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 (Out-of-bounds Write)

## 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.

## Is CVE-2026-80431 being exploited?

There is no known exploitation of CVE-2026-80431 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-80431 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-80431 in the wild and no public exploit code.

Affected product: Kovid Goyal kitty. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-80431/ (Markdown: https://insights.sbomify.com/CVE-2026-80431/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-80431
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-80431
- OSV: https://osv.dev/vulnerability/CVE-2026-80431

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-80431/
Summaries are generated and may contain mistakes; the official description above is the record.