CVE-2021-33670
📋 TL;DR
CVE-2021-33670 is a denial-of-service vulnerability in SAP NetWeaver AS for Java's HTTP Service Monitoring Filter. Attackers can crash the filter by sending multiple HTTP requests with different method types, making the HTTP server unavailable to legitimate users. This affects SAP NetWeaver AS for Java versions 7.10 through 7.50.
💻 Affected Systems
- SAP NetWeaver AS for Java
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete unavailability of HTTP services on affected SAP NetWeaver instances, disrupting business operations that rely on these services.
Likely Case
Intermittent service disruptions and degraded performance of SAP applications running on vulnerable NetWeaver instances.
If Mitigated
Minimal impact with proper network segmentation, rate limiting, and monitoring in place to detect and block attack attempts.
🎯 Exploit Status
Exploitation requires sending crafted HTTP requests but no authentication or special privileges. Public proof-of-concept code exists.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Apply SAP Security Note 3056652
Vendor Advisory: https://launchpad.support.sap.com/#/notes/3056652
Restart Required: Yes
Instructions:
1. Download and apply SAP Security Note 3056652 from SAP Support Portal. 2. Restart the affected SAP NetWeaver instances. 3. Verify the patch is applied correctly.
🔧 Temporary Workarounds
Disable HTTP Service Monitoring Filter
allTemporarily disable the vulnerable filter component if immediate patching is not possible.
Modify filter configuration in SAP NetWeaver administration console
Implement Network Rate Limiting
allConfigure network devices to limit HTTP request rates to prevent exploitation attempts.
Configure rate limiting rules on load balancers or firewalls
🧯 If You Can't Patch
- Isolate affected systems from untrusted networks using firewall rules.
- Implement web application firewall (WAF) rules to block malicious HTTP request patterns.
🔍 How to Verify
Check if Vulnerable:
Check SAP NetWeaver version and verify if Security Note 3056652 is applied via SAP transaction ST03N or system administration tools.Check Version:
Use SAP transaction SM51 or ST03N to check system version and applied patches.Verify Fix Applied:
Confirm Security Note 3056652 is listed as implemented in SAP system patch status. Test HTTP service functionality under normal load.📡 Detection & Monitoring
Log Indicators:
- Unusual spikes in HTTP requests with varying method types
- HTTP Service Monitoring Filter crash messages in system logs
- Increased error rates in HTTP service logs
Network Indicators:
- Multiple HTTP requests with different methods (GET, POST, PUT, etc.) from single sources in short timeframes
- Abnormal HTTP traffic patterns to SAP NetWeaver ports
SIEM Query:
source="sap_netweaver_logs" AND (message="*HTTP Service Monitoring Filter*crash*" OR message="*denial of service*" OR http_method_count > threshold)🔗 References
- http://packetstormsecurity.com/files/166965/SAP-NetWeaver-Java-Denial-Of-Service.html
- http://seclists.org/fulldisclosure/2022/May/4
- https://launchpad.support.sap.com/#/notes/3056652
- https://wiki.scn.sap.com/wiki/pages/viewpage.action?pageId=580617506
- http://packetstormsecurity.com/files/166965/SAP-NetWeaver-Java-Denial-Of-Service.html
- http://seclists.org/fulldisclosure/2022/May/4
- https://launchpad.support.sap.com/#/notes/3056652
- https://wiki.scn.sap.com/wiki/pages/viewpage.action?pageId=580617506
