CVE-2026-34041: act: Unrestricted set-env and add-path command processing enables environment injection

Vulnerability summary

CVE-2026-34041 is a critical (CVSS 9.8) vulnerability in nektos act. EPSS estimates a 0.64% chance of exploitation in the next 30 days, higher than 50.8% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 31-03-2026
   PublishedVulnerability first disclosed.
2. 02-04-2026
   Last modifiedVulnerability information updated.

Description

act is a project which allows for local running of github actions. Prior to version 0.2.86, act unconditionally processes the deprecated ::set-env:: and ::add-path:: workflow commands, which was disabled due to environment injection risks. When a workflow step echoes untrusted data to stdout, an attacker can inject these commands to set arbitrary environment variables or modify the PATH for all subsequent steps in the job. This issue has been patched in version 0.2.86.

• CWE-74Improper Neutralization of Special Elements in Output Used by a Downstream ComponentThe product constructs all or part of a command, data structure, or record using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify how it is parsed or interpreted when it is sent to a downstream component.