# CVE-2026-44638: libsixel: NULL pointer dereference

> A NULL pointer dereference in libsixel causes a crash when memory allocation fails, leading to denial of service for applications using the library.

- **Severity:** Low 2.5 (`CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:N/I:N/A:L`)
- **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-2026-44638, GHSA-wpx3-h5g8-qr3w, UBUNTU-CVE-2026-44638

## What is CVE-2026-44638?

CVE-2026-44638 is a low-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 wrong NULL check after an allocation call in sixel_decode_raw and sixel_decode causes a NULL pointer dereference whenever the allocation fails. The check tests the address of the output parameter (always non-NULL) instead of the value the malloc returned. On allocation failure, the function continues and writes through a NULL pointer, crashing the process. This is a denial of service against any caller of these public APIs that hits a low-memory condition. This vulnerability is fixed in 1.8.7-r2.

Weakness: CWE-690 (Unchecked Return Value to NULL Pointer Dereference), CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2026-44638?

It affects 1 product.


Products: Saitoha Libsixel.

## How do I fix CVE-2026-44638?

Upgrade to a fixed version.

## Is CVE-2026-44638 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-44638 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-2026-44638 and fix it if it is affected.

What it is: CVE-2026-44638 is a low-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-2026-44638 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-2026-44638/ (Markdown: https://insights.sbomify.com/CVE-2026-44638/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-44638
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-44638
- OSV: https://osv.dev/vulnerability/CVE-2026-44638

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-44638/
Summaries are generated and may contain mistakes; the official description above is the record.