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Potential Actions command injection in output filenames (GHSL-2023-275)

High severity GitHub Reviewed Published Dec 29, 2023 in tj-actions/verify-changed-files • Updated Jan 10, 2024

Package

actions tj-actions/verify-changed-files (GitHub Actions)

Affected versions

< 17

Patched versions

17

Description

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

  1. Submit a pull request to the repository with a new file injecting a command. For example $(whoami).txt would be a valid filename.
  2. 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.txt

Impact

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

Published by the National Vulnerability Database Dec 29, 2023
Published to the GitHub Advisory Database Jan 2, 2024
Reviewed Jan 2, 2024
Last updated Jan 10, 2024

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
High
Privileges required
Low
User interaction
None
Scope
Changed
Confidentiality
High
Integrity
Low
Availability
Low

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:L/A:L

EPSS score

0.089%
(39th percentile)

CVE ID

CVE-2023-52137

GHSA ID

GHSA-ghm2-rq8q-wrhc

Credits

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