Emissary, a P2P data-driven workflow engine by the NationalSecurityAgency, contained a command injection vulnerability (CWE-77) in versions before 8.39.0. Specifically, GitHub Actions workflow files used ${{ }} expression syntax to interpolate user-controlled workflow_dispatch inputs directly into shell commands without proper sanitization. This improper neutralization of special elements allowed attackers with write access to the repository to execute arbitrary shell commands. The vulnerability was publicly disclosed with a CVSS 3.1 score of 9.1, indicating critical severity. The issue is resolved in Emissary version 8.39.0.

Successful exploitation allows an attacker with repository write access to execute arbitrary shell commands within GitHub Actions workflows. This can lead to repository poisoning and compromise of the software supply chain, affecting all downstream users who consume the compromised workflows. The impact includes full confidentiality, integrity, and availability loss as indicated by the CVSS vector.

This vulnerability is fixed in Emissary version 8.39.0. Users should upgrade to version 8.39.0 or later to remediate this issue. Since no official patch link or advisory is provided, users should verify the upgrade from the official NationalSecurityAgency Emissary release channels. No additional mitigations are specified.