ghsa-mcph-m25j-8j63
Vulnerability from github
Published
2024-01-02 16:41
Modified
2024-01-02 16:41
Severity ?
7.3 (High) - CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:N
Summary
tj-actions/changed-files has Potential Actions command injection in output filenames (GHSL-2023-271)
Details

Summary

The tj-actions/changed-files workflow allows for command injection in changed filenames, allowing an attacker to execute arbitrary code and potentially leak secrets.

Details

The changed-files action returns a list of files changed in a commit or pull request which provides an escape_json input enabled by default, only escapes " for JSON values.

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 a repository with a new file injecting a command. For example $(whoami).txt which is 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 step below.

yaml - name: List all changed files run: | for file in ${{ steps.changed-files.outputs.all_changed_files }}; do echo "$file was changed" done

Example output:

```yaml

[group]Run for file in $(whoami).txt; do

for file in $(whoami).txt; do
    echo "$file was changed"
done

shell: /usr/bin/bash -e {0}

[endgroup]

runner.txt was changed ```

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.

yaml - name: List all changed files env: ALL_CHANGED_FILES: ${{ steps.changed-files.outputs.all_changed_files }} run: | for file in "$ALL_CHANGED_FILES"; do echo "$file was changed" done

Resources

Show details on source website

To clipboard 

{
  "affected": [
    {
      "package": {
        "ecosystem": "GitHub Actions",
        "name": "tj-actions/changed-files"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "41"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2023-51664"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-74",
      "CWE-77"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2024-01-02T16:41:27Z",
    "nvd_published_at": "2023-12-27T17:15:08Z",
    "severity": "HIGH"
  },
  "details": "### Summary\nThe `tj-actions/changed-files` workflow allows for command injection in changed filenames, allowing an attacker to execute arbitrary code and potentially leak secrets.\n\n### Details\nThe [`changed-files`](https://github.com/tj-actions/changed-files) action returns a list of files changed in a commit or pull request which provides an `escape_json` input [enabled by default](https://github.com/tj-actions/changed-files/blob/94549999469dbfa032becf298d95c87a14c34394/action.yml#L136), only escapes `\"` for JSON values. \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 a repository with a new file injecting a command. For example `$(whoami).txt` which is 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` step below.\n\n```yaml\n      - name: List all changed files\n        run: |\n          for file in ${{ steps.changed-files.outputs.all_changed_files }}; do\n            echo \"$file was changed\"\n          done\n```\n\nExample output:\n\n```yaml\n##[group]Run for file in $(whoami).txt; do\n    for file in $(whoami).txt; do\n        echo \"$file was changed\"\n    done\nshell: /usr/bin/bash -e {0}\n##[endgroup]\nrunner.txt was changed\n```\n\n### Impact\n\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\n  env:\n    ALL_CHANGED_FILES: ${{ steps.changed-files.outputs.all_changed_files }}\n  run: |\n    for file in \"$ALL_CHANGED_FILES\"; do\n      echo \"$file was changed\"\n    done\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/)",
  "id": "GHSA-mcph-m25j-8j63",
  "modified": "2024-01-02T16:41:27Z",
  "published": "2024-01-02T16:41:27Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/tj-actions/changed-files/security/advisories/GHSA-mcph-m25j-8j63"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2023-51664"
    },
    {
      "type": "WEB",
      "url": "https://github.com/tj-actions/changed-files/commit/0102c07446a3cad972f4afcbd0ee4dbc4b6d2d1b"
    },
    {
      "type": "WEB",
      "url": "https://github.com/tj-actions/changed-files/commit/716b1e13042866565e00e85fd4ec490e186c4a2f"
    },
    {
      "type": "WEB",
      "url": "https://github.com/tj-actions/changed-files/commit/ff2f6e6b91913a7be42be1b5917330fe442f2ede"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/tj-actions/changed-files"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "tj-actions/changed-files has Potential Actions command injection in output filenames (GHSL-2023-271)"
}


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