GHSA-GHM2-RQ8Q-WRHC

Vulnerability from github – Published: 2024-01-02 16:42 – Updated: 2024-01-02 16:42
VLAI?
Summary
Potential Actions command injection in output filenames (GHSL-2023-275)
Details

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

Severity ?
7.7 (High)
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:L/A:L
Show details on source website
To clipboard 

{
  "affected": [
    {
      "package": {
        "ecosystem": "GitHub Actions",
        "name": "tj-actions/verify-changed-files"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "17"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2023-52137"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-20",
      "CWE-77"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2024-01-02T16:42:27Z",
    "nvd_published_at": "2023-12-29T17:16:07Z",
    "severity": "HIGH"
  },
  "details": "### Summary\nThe [`tj-actions/verify-changed-files`](https://github.com/tj-actions/verify-changed-files) action allows for command injection in changed filenames, allowing an attacker to execute arbitrary code and potentially leak secrets.\n\n### Details\nThe [`verify-changed-files`](https://github.com/tj-actions/verify-changed-files) workflow returns the list of files changed within a workflow execution.\n\nThis 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](https://docs.github.com/en/actions/using-github-hosted-runners/about-github-hosted-runners) 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`.\n\n#### Proof of Concept\n\n1. Submit a pull request to the repository with a new file injecting a command. For example `$(whoami).txt` would be a valid filename.\n2. 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.\n\n```yaml\n- name: List all changed files tracked and untracked files\n  run: |\n    echo \"Changed files: ${{ steps.verify-changed-files.outputs.changed_files }}\"\n```\n\nExample output:\n\n```yaml\n##[group]Run echo \"Changed files: $(whoami).txt\"\n  echo \"Changed files: $(whoami).txt\"\u001b[0m\nshell: /usr/bin/bash -e {0}\n##[endgroup]\nChanged files: runner.txt\n```\n\n### Impact\nThis issue may lead to arbitrary command execution in the GitHub Runner.\n\n### Resolution\n- A new `safe_output` input would be enabled by default and return filename paths escaping special characters like ;, ` (backtick), $, (), etc for bash environments.\n\n- A safe recommendation of using environment variables to store unsafe outputs.\n\n```yaml\n- name: List all changed files tracked and untracked files\n  env:\n     CHANGED_FILES: ${{ steps.verify-changed-files.outputs.changed_files }}\n  run: |\n    echo \"Changed files: $CHANGED_FILES\"\n```\n\n\n### Resources\n\n* [Keeping your GitHub Actions and workflows secure Part 2: Untrusted input](https://securitylab.github.com/research/github-actions-untrusted-input/)\n* [Keeping your GitHub Actions and workflows secure Part 1: Preventing pwn requests](https://securitylab.github.com/research/github-actions-preventing-pwn-requests/)\n",
  "id": "GHSA-ghm2-rq8q-wrhc",
  "modified": "2024-01-02T16:42:27Z",
  "published": "2024-01-02T16:42:27Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/tj-actions/verify-changed-files/security/advisories/GHSA-ghm2-rq8q-wrhc"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2023-52137"
    },
    {
      "type": "WEB",
      "url": "https://github.com/tj-actions/verify-changed-files/commit/498d3f316f501aa72485060e8c96fde7b2014f12"
    },
    {
      "type": "WEB",
      "url": "https://github.com/tj-actions/verify-changed-files/commit/592e305da041c09a009afa4a43c97d889bed65c3"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/tj-actions/verify-changed-files"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:L/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Potential Actions command injection in output filenames (GHSL-2023-275)"
}


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  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
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  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



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