CVE-2021-20038
📋 TL;DR
A stack-based buffer overflow vulnerability in SonicWall SMA 100 series appliances' Apache httpd mod_cgi module allows remote unauthenticated attackers to execute arbitrary code as the 'nobody' user. This affects SMA 200, 210, 400, 410, and 500v appliances running vulnerable firmware versions. Successful exploitation could lead to complete compromise of the affected appliance.
💻 Affected Systems
- SonicWall SMA 200
- SonicWall SMA 210
- SonicWall SMA 400
- SonicWall SMA 410
- SonicWall SMA 500v
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to full appliance compromise, data exfiltration, lateral movement into connected networks, and persistent backdoor installation.
Likely Case
Remote code execution with 'nobody' user privileges allowing file system access, configuration modification, and potential privilege escalation.
If Mitigated
Denial of service or failed exploitation attempts if proper network segmentation and access controls are implemented.
🎯 Exploit Status
Public exploit code exists in the BadBlood repository. The vulnerability is remotely exploitable without authentication and has been weaponized in real attacks.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Firmware versions after 10.2.0.8-37sv, 10.2.1.1-19sv, and 10.2.1.2-24sv
Vendor Advisory: https://psirt.global.sonicwall.com/vuln-detail/SNWLID-2021-0026
Restart Required: Yes
Instructions:
1. Log into SonicWall SMA appliance management interface. 2. Navigate to System > Settings > Firmware. 3. Download and install the latest firmware version from SonicWall support portal. 4. Reboot the appliance after installation completes.
🔧 Temporary Workarounds
Network Segmentation
allRestrict network access to SMA appliances to only trusted management networks
Web Application Firewall
allDeploy WAF with buffer overflow protection rules to block exploitation attempts
🧯 If You Can't Patch
- Immediately isolate affected appliances from internet and untrusted networks
- Implement strict network access controls allowing only necessary management traffic
🔍 How to Verify
Check if Vulnerable:
Check firmware version in SMA web interface under System > Settings > Firmware. Compare against affected versions: 10.2.0.8-37sv, 10.2.1.1-19sv, 10.2.1.2-24sv and earlier.Check Version:
ssh admin@[sma-ip] show version (or check via web interface)Verify Fix Applied:
Verify firmware version is updated to a version newer than the affected versions listed in the vendor advisory.📡 Detection & Monitoring
Log Indicators:
- Unusual CGI process execution
- Buffer overflow error messages in Apache logs
- Failed authentication attempts followed by successful exploitation
Network Indicators:
- HTTP requests with unusually long environment variables
- Traffic patterns matching known exploit signatures
- Outbound connections from SMA appliance to unexpected destinations
SIEM Query:
source="sma_logs" AND ("mod_cgi" OR "buffer overflow" OR "segmentation fault")🔗 References
- https://github.com/jbaines-r7/badblood
- https://psirt.global.sonicwall.com/vuln-detail/SNWLID-2021-0026
- https://www.rapid7.com/blog/post/2022/01/11/cve-2021-20038-42-sonicwall-sma-100-multiple-vulnerabilities-fixed-2/
- https://github.com/jbaines-r7/badblood
- https://psirt.global.sonicwall.com/vuln-detail/SNWLID-2021-0026
- https://www.rapid7.com/blog/post/2022/01/11/cve-2021-20038-42-sonicwall-sma-100-multiple-vulnerabilities-fixed-2/
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-20038
