Description

Fork-PR Actions task can read a third private repository via the collaborative-owner branch (missing fork-PR guard)

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "7.1",
  "pubDate": "2026-08-13T17:17:26.300Z",
  "pubdate": "2026-08-13T17:17:26.300Z",
  "executiveSummary": "A vulnerability exists in the Fork-PR Actions task mechanism where it can read a third private repository via the collaborative-owner branch due to a missing fork-PR guard.\nThis security flaw allows unauthorized entities to access sensitive private repository data that should otherwise be restricted.\nThe affected systems include CI/CD pipelines and workflow automation environments utilizing Fork-PR Actions tasks configured with collaborative-owner branch capabilities.\nThe risk implications involve severe data exposure, potential compromise of proprietary source code, and leakage of internal credentials or configuration details.\nAn attacker with the capability to submit a pull request can exploit this behavior without requiring elevated privileges within the targeted private repository.\nSuccessful exploitation hinges on the lack of proper authorization checks and boundary validations when processing untrusted fork pull requests against collaborative branches.",
  "technicalDetails": "The root cause of this vulnerability lies in the absence of a proper fork-PR guard within the Fork-PR Actions task execution logic.\nWhen a pull request is initiated from a forked repository targeting the collaborative-owner branch, the execution context fails to validate whether the source context is authorized to interact with or read assets from a third private repository.\nThe vulnerable component is the workflow execution handler responsible for fetching repository contents and resolving branch references during external pull request events.\nExploitation occurs because the automation script or task trusts the incoming event parameters and executes file read operations across repository boundaries without enforcing strict access control lists or token scope restrictions.\nThe attack flow proceeds as follows: First, an attacker crafts a malicious pull request originating from an external fork.\nSecond, the workflow triggers the Fork-PR Actions task pointing to the collaborative-owner branch.\nThird, due to the missing fork-PR guard, the task executes with permissions capable of accessing the third private repository.\nFourth, the attacker extracts sensitive data by leveraging the workflow's read capabilities to exfiltrate contents from the private repository.\nNetwork exposure is defined by the scope of the CI/CD environment and the permissions assigned to the workflow tokens.\nAuthentication and privilege requirements are minimal for the attacker, as standard public fork contributions can be leveraged to trigger the vulnerable workflow behavior.\nPost-exploitation impact includes unauthorized data exfiltration, exposure of intellectual property, and potential escalation if secondary secrets are embedded within the accessed private repository."
}