Summary
The tj-actions/verify-changed-files action allows for command injection in changed filenames, allowing an attacker to execute arbitrary code and potentially leak secrets.
Details
The verify-changed-files workflow returns the list of files changed within a workflow execution.
This could potentially allow filenames that contain special characters such as ; and ` (backtick) which can be used by an attacker to take over the GitHub Runner if the output value is used in a raw fashion (thus being directly replaced before execution) inside a run block. By running custom commands an attacker may be able to steal secrets such as GITHUB_TOKEN if triggered on other events than pull_request. For example on push.
Proof of Concept
- Submit a pull request to the repository with a new file injecting a command. For example
$(whoami).txt would be a valid filename.
- Upon approval of the workflow (triggered by the pull request), the action will get executed and the malicious pull request filename will flow into the
List all changed files tracked and untracked files step.
- name: List all changed files tracked and untracked files
run: |
echo "Changed files: ${{ steps.verify-changed-files.outputs.changed_files }}"Example output:
##[group]Run echo "Changed files: $(whoami).txt"
echo "Changed files: $(whoami).txt"�[0m
shell: /usr/bin/bash -e {0}
##[endgroup]
Changed files: runner.txtImpact
This issue may lead to arbitrary command execution in the GitHub Runner.
Resolution
-
A new safe_output input would be enabled by default and return filename paths escaping special characters like ;, ` (backtick), $, (), etc for bash environments.
-
A safe recommendation of using environment variables to store unsafe outputs.
- name: List all changed files tracked and untracked files
env:
CHANGED_FILES: ${{ steps.verify-changed-files.outputs.changed_files }}
run: |
echo "Changed files: $CHANGED_FILES"Resources
References
Summary
The
tj-actions/verify-changed-filesaction allows for command injection in changed filenames, allowing an attacker to execute arbitrary code and potentially leak secrets.Details
The
verify-changed-filesworkflow returns the list of files changed within a workflow execution.This could potentially allow filenames that contain special characters such as
;and ` (backtick) which can be used by an attacker to take over the GitHub Runner if the output value is used in a raw fashion (thus being directly replaced before execution) inside arunblock. By running custom commands an attacker may be able to steal secrets such asGITHUB_TOKENif triggered on other events thanpull_request. For example onpush.Proof of Concept
$(whoami).txtwould be a valid filename.List all changed files tracked and untracked filesstep.Example output:
Impact
This issue may lead to arbitrary command execution in the GitHub Runner.
Resolution
A new
safe_outputinput would be enabled by default and return filename paths escaping special characters like ;, ` (backtick), $, (), etc for bash environments.A safe recommendation of using environment variables to store unsafe outputs.
Resources
References