# CVE-2026-25121: apko is vulnerable to path traversal in apko dirFS which allows filesystem writes outside base

> Attackers can write files outside the intended directory via malicious APK packages, potentially compromising the build environment.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 4 Feb 2026
- **Updated:** 4 Feb 2026
- **Also known as:** GHSA-5g94-c2wx-8pxw, GO-2026-4405, MINI-fm7j-w2v8-v2mj

## What is CVE-2026-25121?

CVE-2026-25121 is a high-severity path traversal vulnerability in chainguard-dev apko, published on 4 Feb 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

apko allows users to build and publish OCI container images built from apk packages. From version 0.14.8 to before 1.1.1, a path traversal vulnerability was discovered in apko's dirFS filesystem abstraction. An attacker who can supply a malicious APK package (e.g., via a compromised or typosquatted repository) could create directories or symlinks outside the intended installation root. The MkdirAll, Mkdir, and Symlink methods in pkg/apk/fs/rwosfs.go use filepath.Join() without validating that the resulting path stays within the base directory. This issue has been patched in version 1.1.1.

Weakness: CWE-22 (Improper Limitation of a Pathname to a Restricted Directory), CWE-23 (Relative Path Traversal)

## Which versions are affected by CVE-2026-25121?

3 open source packages ship an affected version, including chainguard.dev/apko. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `chainguard.dev/apko` | Go | From 0.14.8 | 1.1.0 |
| `chainguard.dev/apko` | Go | From 0.14.8 | 1.1.0 |
| `chainguard.dev/apko` | Go | From 0.14.8 | 1.1.0 |

Products: Chainguard Apko.

## How do I fix CVE-2026-25121?

Upgrade chainguard.dev/apko to 1.1.0 or later.

## Is CVE-2026-25121 being exploited?

There is no known exploitation of CVE-2026-25121 in the wild and no public exploit code.

## Other vulnerabilities in chainguard-dev apko

- [CVE-2026-25140](https://insights.sbomify.com/CVE-2026-25140/): apko affected by potential unbounded resource consumption in expandapk.ExpandApk on attacker-controlled .apk streams (high 7.5)
- [CVE-2026-25122](https://insights.sbomify.com/CVE-2026-25122/): apko is vulnerable to unbounded resource consumption in expandapk.Split on attacker-controlled .apk streams (medium 5.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-25121 and fix it if it is affected.

What it is: CVE-2026-25121 is a high-severity path traversal vulnerability in chainguard-dev apko, published on 4 Feb 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-25121 in the wild and no public exploit code.

Affected packages and fixed versions:
- chainguard.dev/apko (Go): affected from 0.14.8; fixed in 1.1.0
- chainguard.dev/apko (Go): affected from 0.14.8; fixed in 1.1.0
- chainguard.dev/apko (Go): affected from 0.14.8; fixed in 1.1.0

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-2026-25121/ (Markdown: https://insights.sbomify.com/CVE-2026-25121/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-25121
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-25121
- OSV: https://osv.dev/vulnerability/CVE-2026-25121

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-25121/
Summaries are generated and may contain mistakes; the official description above is the record.