# CVE-2026-44636: libsixel: integer overflow in encoder

> An integer overflow in libsixel's encoder allows heap buffer overflows when processing large image dimensions, potentially leading to code execution or crashes.

- **Severity:** High 7.4 (`CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 14 May 2026
- **Updated:** 16 May 2026
- **Also known as:** DEBIAN-CVE-2026-44636, GHSA-hx93-w8p2-ffh5, UBUNTU-CVE-2026-44636

## What is CVE-2026-44636?

CVE-2026-44636 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, with no action from the victim.

### Official description

libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel. From  to 1.8.7-r1, signed integer overflow in sixel_encode_highcolor's allocation size calculation can lead to a heap buffer overflow. The public sixel_encode entry point validates only that width and height are greater than zero, with no upper bound. width and height are multiplied as plain int when computing the allocation size for paletted_pixels and normalized_pixels. Any caller that asks libsixel to encode a pixel buffer with width times height greater than INT_MAX (about 2.15 billion) will hit a wrapped allocation size; under the right wrap, the malloc succeeds with a buffer much smaller than the encoder expects, and the encoder writes past the end of the heap allocation. This vulnerability is fixed in 1.8.7-r2.

Weakness: CWE-190 (Integer Overflow or Wraparound), CWE-122 (Heap-based Buffer Overflow)

## Which versions are affected by CVE-2026-44636?

It affects 1 product.


Products: Saitoha Libsixel.

## How do I fix CVE-2026-44636?

Upgrade to a fixed version.

## Is CVE-2026-44636 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-44636 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-2026-44636 and fix it if it is affected.

What it is: CVE-2026-44636 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, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-44636 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-2026-44636/ (Markdown: https://insights.sbomify.com/CVE-2026-44636/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-44636
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-44636
- OSV: https://osv.dev/vulnerability/CVE-2026-44636

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-44636/
Summaries are generated and may contain mistakes; the official description above is the record.