# CVE-2026-64846: Nix: Arbitrary file truncation outside the sandbox with recursive-nix experimental feature


- **Severity:** Low 2.8 (`CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:N/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Fix available:** No
- **Published:** 20 Aug 2026
- **Updated:** 20 Aug 2026
- **Also known as:** DEBIAN-CVE-2026-64846, GHSA-6h4g-g5j9-fm5f, UBUNTU-CVE-2026-64846

## What is CVE-2026-64846?

CVE-2026-64846 is a low-severity vulnerability in NixOS nix, published on 20 Aug 2026. 

### Official description

Nix is a package manager for Linux and other Unix systems. Prior to 2.35.0, a malicious derivation executed with the recursive-nix experimental feature can exploit a time-of-check/time-of-use race involving final symlink handling in the LocalStore restore path. The race can cause writeFile to follow a substituted final symlink when opening a path with O_TRUNC instead of enforcing FinalSymlink::DontFollow, allowing the Nix process or nix-daemon to create or truncate an empty file outside the build sandbox with the daemon user's permissions. The primitive does not provide arbitrary-content writes and requires winning the race. This issue is fixed in version 2.35.0.

Weakness: CWE-61 (UNIX Symbolic Link (Symlink) Following), CWE-367 (Time-of-check Time-of-use (TOCTOU) Race Condition)

## Which versions are affected by CVE-2026-64846?


## How do I fix CVE-2026-64846?

No fix has been published for CVE-2026-64846 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-64846 being exploited?

There is no known exploitation of CVE-2026-64846 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-64846 and fix it if it is affected.

What it is: CVE-2026-64846 is a low-severity vulnerability in NixOS nix, published on 20 Aug 2026. 
Exploitation: There is no known exploitation of CVE-2026-64846 in the wild and no public exploit code.

Affected product: NixOS nix. 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-2026-64846/ (Markdown: https://insights.sbomify.com/CVE-2026-64846/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-64846
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-64846
- OSV: https://osv.dev/vulnerability/CVE-2026-64846

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-64846/
Summaries are generated and may contain mistakes; the official description above is the record.