nix-nar: Decoder::unpack writes archive entries outside the destination directory (path traversal)

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

EPSS

No dated EPSS signal available.

As published by the source; long descriptions are shortened.

`Decoder::unpack` does not safely contain the paths it extracts, so a malicious NAR archive can create files outside the destination directory — a path traversal (CWE-22). In `src/dec.rs` (`Decoder::unpack`): - A symlink entry's target is written without checking where it points (`src/dec.rs:153`), so the archive can create a symlink that escapes the destination directory. - The out-of-destination containment check compares path strings only and does not account for symlinks created earlier in the same unpack (`src/dec.rs:176-181`), before reaching the write sinks (`std::fs::create_dir` at `src/dec.rs:201` and `OpenOptions::open` at `src/dec.rs:218`). - The parser also accepts entry names containing `/` (`src/parser.rs:138-147`). Combined, a malicious archive can include a symlink `a` pointing at an external directory and then an entry named `a/b`, causing `b` to be written to ` /b`, outside the destination. This can create new files anywhere the process can write (it cannot…

Published by the source

30 Oct 2026, 12:00 UTC

Last modified by the source

30 Oct 2026, 10:45 UTC

Source last checked

31 Oct 2026, 06:45 UTC

1. Revision 1 · created · 31 Oct 2026

   Published from osv record RUSTSEC-2026-0425

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# Patch Next advisory brief: rustsec-2026-0425

Advisory: `nix-nar`: `Decoder::unpack` writes archive entries outside the destination directory (path traversal)
IDs: rustsec-2026-0425
Record: https://patchnext.com/advisories/rustsec-2026-0425 (revision 1, source checked 31 Oct 2026, 06:45 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: nix-nar 0.6.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io nix-nar: affected >= 0.0.0-0, < 0.6.0; fixed in 0.6.0

## Suggested inspection (read-only)
- crates.io nix-nar: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on nix-nar.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/RUSTSEC-2026-0425 (OSV record RUSTSEC-2026-0425 lists affected ranges: crates.io nix-nar >=0.0.0-0 <0.6.0 (fixed))

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