CVE-2021-32647
📋 TL;DR
This vulnerability allows authenticated attackers to execute arbitrary code on Emissary workflow engine servers by exploiting a class loading mechanism in the CreatePlace REST endpoint. Attackers can load malicious classes that may lead to remote code execution, application crashes, or data leakage. Organizations using affected Emissary versions are at risk.
💻 Affected Systems
- Emissary
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise through remote code execution, allowing attackers to execute arbitrary commands, install malware, or pivot to other systems.
Likely Case
Application disruption through denial of service (crashing the application) or limited code execution using available gadget classes in the classpath.
If Mitigated
Limited impact if proper network segmentation and authentication controls prevent unauthorized access to the vulnerable endpoint.
🎯 Exploit Status
Exploitation requires authentication and finding suitable gadget classes in the application classpath, but the vulnerability is straightforward to trigger once these conditions are met.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check latest Emissary releases for fix
Vendor Advisory: https://github.com/NationalSecurityAgency/emissary/security/advisories/GHSA-ph73-7v9r-wg32
Restart Required: Yes
Instructions:
1. Update Emissary to the latest patched version. 2. Restart the Emissary service. 3. Verify the CreatePlace endpoint no longer accepts arbitrary class names.
🔧 Temporary Workarounds
Network Access Restriction
linuxBlock network access to Emissary from untrusted sources to prevent attackers from reaching the vulnerable endpoint.
iptables -A INPUT -p tcp --dport [emissary_port] -s [trusted_network] -j ACCEPT
iptables -A INPUT -p tcp --dport [emissary_port] -j DROP
🧯 If You Can't Patch
- Implement strict network segmentation to isolate Emissary servers from untrusted networks
- Enhance authentication controls and monitor for suspicious access to the CreatePlace endpoint
🔍 How to Verify
Check if Vulnerable:
Check if your Emissary version is affected by reviewing the version number against the advisory. Test if the CreatePlace endpoint accepts arbitrary sppClassName parameters.Check Version:
Check Emissary documentation or configuration files for version informationVerify Fix Applied:
After patching, attempt to trigger the vulnerability with a test payload. The endpoint should reject or sanitize arbitrary class names.📡 Detection & Monitoring
Log Indicators:
- Unusual requests to /CreatePlace endpoint with suspicious sppClassName parameters
- Class loading errors or exceptions in application logs
Network Indicators:
- HTTP POST requests to CreatePlace endpoint with unusual class names in parameters
SIEM Query:
source="emissary.logs" AND (uri_path="/CreatePlace" AND sppClassName!="")🔗 References
- https://github.com/NationalSecurityAgency/emissary/blob/30c54ef16c6eb6ed09604a929939fb9f66868382/src/main/java/emissary/server/mvc/internal/CreatePlaceAction.java#L36
- https://github.com/NationalSecurityAgency/emissary/security/advisories/GHSA-ph73-7v9r-wg32
- https://github.com/NationalSecurityAgency/emissary/blob/30c54ef16c6eb6ed09604a929939fb9f66868382/src/main/java/emissary/server/mvc/internal/CreatePlaceAction.java#L36
- https://github.com/NationalSecurityAgency/emissary/security/advisories/GHSA-ph73-7v9r-wg32
