The vulnerability in Gitea act_runner with Docker backend (through act 0.262.0) involves improper privilege management. When configured with privileged: false, the system disables only the Privileged flag but merges other Docker options such as --pid=host, --cap-add, and --security-opt without restriction. This allows a user who can run workflows on a Docker-backed runner to create a job container that has host namespaces and broad capabilities, enabling container escape to the host with root privileges. The CVSS 3.1 score is 9.9 (critical), reflecting network attack vector, low attack complexity, low privileges required, no user interaction, scope change, and high impact on confidentiality, integrity, and availability.

An attacker with permission to run workflows on a Docker-backed Gitea act_runner can escalate privileges by creating containers with host namespaces and elevated capabilities despite privileged mode being disabled. This can lead to container escape and full root access on the host system, compromising confidentiality, integrity, and availability of the host and potentially other workloads.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is available, restrict workflow execution permissions to trusted users only and avoid running untrusted workflows on Docker-backed runners. Monitor vendor channels for updates and apply patches promptly once released.