# CVE-2026-44637: libsixel: integer overflow in parser

> A signed integer overflow in the libsixel SIXEL parser allows attackers to trigger an out-of-bounds heap write via crafted image data, potentially leading to code execution.

- **Severity:** High 7.1 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H`)
- **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:** Yes
- **Published:** 14 May 2026
- **Updated:** 15 May 2026
- **Also known as:** DEBIAN-CVE-2026-44637, GHSA-9jm7-77gr-qghv, UBUNTU-CVE-2026-44637

## What is CVE-2026-44637?

CVE-2026-44637 is a high-severity vulnerability in saitoha libsixel, published on 14 May 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

libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel. From  to 1.8.7-r1, a signed integer overflow in the SIXEL parser's image-buffer doubling loop can lead to an out-of-bounds heap write in sixel_decode_raw_impl. context->pos_x grows by repeat_count on every sixel character with no upper bound check. Once pos_x approaches INT_MAX, the expression "pos_x + repeat_count" used to size the image buffer overflows signed int. Depending on how the overflow wraps, the resize check that should reject oversized buffers can be bypassed, after which a subsequent write computes a large attacker-influenced offset into image->data and writes past the allocation. Reachable from any caller that decodes attacker-supplied SIXEL data, including img2sixel. This vulnerability is fixed in 1.8.7-r2.

Weakness: CWE-787 (Out-of-bounds Write), CWE-190 (Integer Overflow or Wraparound)

## Which versions are affected by CVE-2026-44637?

It affects 1 product.


Products: Saitoha Libsixel.

## How do I fix CVE-2026-44637?

Upgrade to a fixed version.

## Is CVE-2026-44637 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-44637 exists.

## Other vulnerabilities in saitoha libsixel

- [CVE-2019-19635](https://insights.sbomify.com/CVE-2019-19635/): Memory corruption in n/a (critical 9.8)
- [CVE-2019-19636](https://insights.sbomify.com/CVE-2019-19636/): Integer overflow in n/a (critical 9.8)
- [CVE-2019-19637](https://insights.sbomify.com/CVE-2019-19637/): Integer overflow in n/a (critical 9.8)
- [CVE-2019-19638](https://insights.sbomify.com/CVE-2019-19638/): Integer overflow in n/a (critical 9.8)
- [CVE-2022-27044](https://insights.sbomify.com/CVE-2022-27044/): Memory corruption in n/a (high 8.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-44637 and fix it if it is affected.

What it is: CVE-2026-44637 is a high-severity vulnerability in saitoha libsixel, published on 14 May 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: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-44637 exists.

Affected product: saitoha libsixel. 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-2026-44637/ (Markdown: https://insights.sbomify.com/CVE-2026-44637/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-44637
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-44637
- OSV: https://osv.dev/vulnerability/CVE-2026-44637

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-44637/
Summaries are generated and may contain mistakes; the official description above is the record.