# CVE-2026-34042: act: actions/cache server allows malicious cache injection

> Attackers can inject malicious caches into the local GitHub Actions runner, potentially leading to arbitrary code execution within the container.

- **Severity:** High 8.2 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 31 Mar 2026
- **Updated:** 31 Mar 2026
- **Also known as:** GHSA-x34h-54cw-9825, GO-2026-4890

## What is CVE-2026-34042?

CVE-2026-34042 is a high-severity missing authorization vulnerability in nektos act, published on 31 Mar 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

act is a project which allows for local running of github actions. Prior to version 0.2.86, act's built in actions/cache server listens to connections on all interfaces and allows anyone who can connect to it including someone anywhere on the internet to create caches with arbitrary keys and retrieve all existing caches. If they can predict which cache keys will be used by local actions, they can create malicious caches containing whatever files they please most likely allowing arbitrary remote code execution within the docker container. This issue has been patched in version 0.2.86.

Weakness: CWE-862 (Missing Authorization)

## Which versions are affected by CVE-2026-34042?

3 open source packages ship an affected version, including github.com/nektos/act.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/nektos/act` | Go | All versions | 0.2.86 |
| `github.com/nektos/act` | Go | All versions | 0.2.86 |
| `github.com/nektos/act` | Go | All versions | 0.2.86 |

## How do I fix CVE-2026-34042?

Upgrade github.com/nektos/act to 0.2.86 or later.

## Is CVE-2026-34042 being exploited?

There is no known exploitation of CVE-2026-34042 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-34042 and fix it if it is affected.

What it is: CVE-2026-34042 is a high-severity missing authorization vulnerability in nektos act, published on 31 Mar 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-34042 in the wild and no public exploit code.

Affected packages and fixed versions:
- github.com/nektos/act (Go): affected all versions; fixed in 0.2.86
- github.com/nektos/act (Go): affected all versions; fixed in 0.2.86
- github.com/nektos/act (Go): affected all versions; fixed in 0.2.86

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-2026-34042/ (Markdown: https://insights.sbomify.com/CVE-2026-34042/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-34042
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-34042
- OSV: https://osv.dev/vulnerability/CVE-2026-34042

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-34042/
Summaries are generated and may contain mistakes; the official description above is the record.