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.
- 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
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
Which versions are affected by CVE-2026-34042?
3 open source packages ship an affected version, including github.com/nektos/act.
| Package | 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.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2026-34042 being exploited?
There is no known exploitation of CVE-2026-34042 in the wild and no public exploit code.
Sources
Also known as GHSA-x34h-54cw-9825, GO-2026-4890.