# CVE-2026-79591: Use after free in n/a

> A heap-buffer-overflow and use-after-free in libxls allows attackers to execute arbitrary code or cause denial of service via crafted files.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:R/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:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 10 Sep 2026
- **Updated:** 15 Sep 2026
- **Also known as:** DEBIAN-CVE-2026-79591, GHSA-8cvq-g9xh-jmpf, UBUNTU-CVE-2026-79591

## What is CVE-2026-79591?

CVE-2026-79591 is a high-severity use after free vulnerability in n/a, published on 10 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

A heap-buffer-overflow and use-after-free vulnerability exists in the xls_getCSS() function of libxls 1.6.3 due to insufficient validation of a file-controlled font index.

Weakness: CWE-122 (Heap-based Buffer Overflow)

## Which versions are affected by CVE-2026-79591?


## How do I fix CVE-2026-79591?

Upgrade to a fixed version.

## Is CVE-2026-79591 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-79591 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-79591 and fix it if it is affected.

What it is: CVE-2026-79591 is a high-severity use after free vulnerability in n/a, published on 10 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: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-79591 exists.

Affected product: n/a. 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-2026-79591/ (Markdown: https://insights.sbomify.com/CVE-2026-79591/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-79591
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-79591
- OSV: https://osv.dev/vulnerability/CVE-2026-79591

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-79591/
Summaries are generated and may contain mistakes; the official description above is the record.