vulnerabilities-workflow-1.md

Combined Vulnerability List

Initial analysis of the project files did not reveal any high-rank vulnerabilities exploitable by an external attacker in a publicly available instance of the application. However, further investigation identified a potential vulnerability in a CI script, which, while not directly part of the application runtime, could pose a risk to the development and build process.

Vulnerability: Git Checkout Option Injection in CI Script (_tools/apidiff.sh)

• Description: The CI helper script _tools/apidiff.sh uses user-provided input as a Git reference without proper sanitization. Specifically, the script accepts a branch or tag value via the -r parameter and uses it in a git checkout command:

  git -C "${clone}" co "${ref}"

  The script lacks validation to ensure that the provided reference (${ref}) does not start with a hyphen. Consequently, if an attacker can control the -r parameter (e.g., through a malicious branch name in a pull request), they could inject Git options like --detach or -f. Git would then interpret these values as command options instead of branch names, potentially altering the intended behavior of the git checkout command within the CI workflow.

• Impact: Exploiting this vulnerability could allow an attacker to:

  • Manipulate CI Pipeline Behavior: By injecting Git options, an attacker can alter the checkout process, potentially leading to unintended states like a detached HEAD. This can disrupt the intended flow of the CI pipeline, causing tests to run in an incorrect context or preventing them from running altogether.
  • Circumvent API Difference Tests: By altering the checkout, an attacker might be able to bypass or manipulate the API difference tests, leading to undetected regressions or vulnerabilities being introduced.
  • Expose Sensitive Information: Modified Git commands could potentially output sensitive build or repository information, depending on the injected options and the CI environment setup.
  • Compromise Build Integrity: Changes to the checkout process could lead to builds being generated from unintended code states, compromising the integrity of the final build artifacts. While this vulnerability is not a direct path to remote code execution on a publicly facing application instance, it presents a significant risk to the development pipeline's integrity and reliability.

• Vulnerability Rank: High

• Currently Implemented Mitigations:

  • Double Quotes: The script uses double quotes around the ${ref} variable ("${ref}"). This prevents shell word splitting and pathname expansion, but it does not prevent Git from interpreting arguments starting with a hyphen as options.
  • getopts for Argument Parsing: The script utilizes getopts for parsing command-line arguments, which enforces a structured approach to option handling in the script. However, getopts itself does not provide input validation against malicious option injection in the context of Git commands.

• Missing Mitigations:

  • Input Validation: Implement validation for the -r parameter to reject any input that begins with a hyphen (-). This would prevent the injection of Git options through this parameter.
  • End-of-Options Delimiter (--): Modify the git checkout command to include the end-of-options delimiter -- before the ${ref} variable. This ensures that Git treats everything following -- as literal arguments (branch/tag names) and not as command-line options. The corrected command would be:

    git -C "${clone}" co -- "${ref}"

• Preconditions:

  • Control over -r Parameter: An attacker must be able to influence or control the value passed to the -r parameter of the _tools/apidiff.sh script. In the context of the provided GitHub Actions workflow (.github/workflows/apidiff.yaml), this parameter is indirectly derived from github.base_ref.
  • CI Accepts External Contributions: The CI environment must be configured to process pull requests or other events that could be initiated or influenced by external contributors, where branch names or base references might be under their control.

• Source Code Analysis:

  1. Input Handling with getopts: The script uses getopts to parse command-line arguments, including the -r option:

     while getopts "r:" opt; do
         case "$opt" in
             r) ref="$OPTARG" ;;
             *) usage; exit 1 ;;
         esac
     done

     This section reads the value provided with the -r option and stores it in the ref variable.

  2. Git Checkout Command: Later in the script, the ref variable is used in the git checkout command:

     if [[ -n "${ref}" ]]; then
         git -C "${clone}" co "${ref}"
     fi

     The ${ref} variable is correctly quoted to prevent word splitting. However, the lack of the -- delimiter before ${ref} means that Git will still interpret any argument starting with a hyphen as a potential option.

  3. Vulnerability Trigger: If an attacker provides a value for -r that starts with a hyphen (e.g., --detach), the executed command becomes something like:

     git -C /tmp/clone co "--detach"

     Git interprets --detach as the --detach option, not as a branch name, leading to unintended behavior.

  4. Visualization:

     graph LR
         A[Script starts] --> B{Parse arguments with getopts};
         B --> C{Check for -r option};
         C -- Yes --> D{ref="$OPTARG"};
         C -- No --> E{Continue script};
         D --> F{Git checkout with "${ref}"};
         F --> G[Script continues];
     
         subgraph Normal Flow
             H[User provides: -r master] --> I{${ref} = "master"};
             I --> J[git co "master"];
             J --> K[Checkout 'master' branch];
         end
     
         subgraph Exploit Flow
             L[Attacker provides: -r "--detach"] --> M{${ref} = "--detach"};
             M --> N[git co "--detach"];
             N --> O[Git interprets "--detach" as option];
             O --> P[Unintended Git behavior (e.g., detached HEAD)];
         end
     

     Loading

• Security Test Case:

  1. Setup:

     • Fork the repository.
     • Set up a test CI environment or utilize the existing GitHub Actions workflow of your fork.
     • Ensure you have control over triggering CI workflows, for instance, by creating and pushing branches and opening pull requests.

  2. Test Steps:

     • Create a new branch in your forked repository with a name that starts with a hyphen. For example, name the branch --test-exploit.
     • Push this branch to your fork (git push origin --test-exploit).
     • Open a pull request from your --test-exploit branch to the main branch of your fork. This should trigger the CI workflow defined in .github/workflows/apidiff.yaml.
     • Monitor the logs of the triggered CI workflow, specifically looking at the output of the _tools/apidiff.sh script, especially the Git checkout step.

  3. Validation:

     • Examine the CI logs for the Git checkout command execution.
     • Successful Exploitation: If the Git command output indicates unexpected behavior, such as error messages related to option parsing, help messages from Git, or if the checkout results in a detached HEAD state (which can be indicated in Git output), it confirms that the hyphenated branch name was misinterpreted as a Git option.
     • Expected Behavior (without exploit): In a normal, non-vulnerable scenario, Git would attempt to checkout a branch named --test-exploit (which likely doesn't exist, but it would try to treat it as a branch name, not an option).

  4. Post-Test & Remediation Verification:

     • After confirming the vulnerability, implement the proposed mitigations: add input validation to reject hyphen-starting -r values and use -- before ${ref} in the git checkout command.
     • Repeat the test case with the mitigated script. Verify that the CI workflow now either rejects the hyphenated input or correctly attempts to checkout a branch named --test-exploit without misinterpreting it as an option, indicating the vulnerability is resolved.

By implementing the suggested missing mitigations, specifically input validation and using the -- delimiter, the Git Checkout Option Injection vulnerability in the _tools/apidiff.sh script can be effectively resolved, enhancing the security and reliability of the CI pipeline.