CVE-2026-27203
📋 TL;DR
The eBay API MCP Server is vulnerable to environment variable injection through the updateEnvFile function, which doesn't validate input for newlines or quotes. This allows attackers to inject arbitrary environment variables into the configuration file, potentially leading to configuration overwrites, denial of service, or remote code execution. All users running the eBay API MCP Server are affected.
💻 Affected Systems
- eBay API MCP Server
⚠️ Manual Verification Required
This CVE does not have specific version information in our database, so automatic vulnerability detection cannot determine if your system is affected.
Why? The CVE database entry doesn't specify which versions are vulnerable (no version ranges provided by the vendor/NVD).
🔒 Custom verification scripts are available for registered users. Sign up free to download automated test scripts.
- Review the CVE details at NVD
- Check vendor security advisories for your specific version
- Test if the vulnerability is exploitable in your environment
- Consider updating to the latest version as a precaution
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise, data exfiltration, or lateral movement within the network.
Likely Case
Configuration file corruption leading to denial of service or unauthorized access to eBay API functionality.
If Mitigated
Limited impact with proper input validation and restricted file permissions preventing injection.
🎯 Exploit Status
Exploitation requires access to the ebay_set_user_tokens tool, but the injection technique is straightforward once access is obtained.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: None
Vendor Advisory: https://github.com/YosefHayim/ebay-mcp/security/advisories/GHSA-97rm-xj73-33jh
Restart Required: No
Instructions:
No official patch is available. Monitor the GitHub repository for updates and apply any future patches that implement proper input validation in the updateEnvFile function.
🔧 Temporary Workarounds
Restrict access to ebay_set_user_tokens tool
linuxLimit access to the vulnerable tool to trusted users only.
chmod 700 /path/to/ebay_set_user_tokens
chown root:root /path/to/ebay_set_user_tokens
Implement manual input validation
allModify the updateEnvFile function to validate input for newlines and quotes before writing to the .env file.
Edit src/auth/oauth.ts to add input validation logic
🧯 If You Can't Patch
- Disable or remove the ebay_set_user_tokens tool entirely if not required.
- Implement strict file permissions on the .env file to prevent unauthorized writes (e.g., chmod 600 .env).
🔍 How to Verify
Check if Vulnerable:
Check if the updateEnvFile function in src/auth/oauth.ts lacks validation for newlines or quotes in input values.Check Version:
Check the project's package.json or version file for current version information.Verify Fix Applied:
Verify that the updateEnvFile function now properly sanitizes input by rejecting or escaping newlines and quotes.📡 Detection & Monitoring
Log Indicators:
- Unusual modifications to the .env file
- Multiple failed attempts to update environment variables
- Unexpected new environment variables being set
Network Indicators:
- Unusual API calls to the eBay MCP Server endpoints related to token updates
SIEM Query:
source="ebay-mcp" AND (event="env_update" AND (message="*\n*" OR message="*\"*"))