CVE-2021-21874
📋 TL;DR
This vulnerability allows authenticated attackers to execute arbitrary commands on affected systems by sending specially crafted HTTP requests containing malicious input in the DSA keypasswd parameter. It affects systems running vulnerable versions of the software that expose the affected functionality. Attackers with valid credentials can exploit this to gain full control of the target system.
💻 Affected Systems
- DSA (Digital Signature Algorithm) implementation with vulnerable keypasswd parameter handling
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise leading to data theft, lateral movement, ransomware deployment, or persistent backdoor installation.
Likely Case
Unauthorized command execution leading to data exfiltration, privilege escalation, or service disruption.
If Mitigated
Limited impact due to network segmentation, strong authentication controls, and minimal user privileges.
🎯 Exploit Status
Exploitation requires authentication but is straightforward once credentials are obtained; public proof-of-concept exists in Talos reports.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check vendor-specific advisory for patched version
Vendor Advisory: https://talosintelligence.com/vulnerability_reports/TALOS-2021-1314
Restart Required: Yes
Instructions:
1. Identify affected software version. 2. Apply vendor-provided patch. 3. Restart affected services. 4. Verify fix implementation.
🔧 Temporary Workarounds
Input Validation Filter
allImplement strict input validation to reject malicious characters in the keypasswd parameter
# Configure web application firewall or input filter rules specific to your environment
Access Restriction
linuxRestrict network access to vulnerable endpoints using firewall rules
iptables -A INPUT -p tcp --dport [PORT] -s [TRUSTED_IPS] -j ACCEPT
iptables -A INPUT -p tcp --dport [PORT] -j DROP
🧯 If You Can't Patch
- Implement network segmentation to isolate vulnerable systems from critical assets
- Enforce strong authentication mechanisms and monitor for credential compromise
🔍 How to Verify
Check if Vulnerable:
Review system logs for suspicious HTTP requests to endpoints with keypasswd parameter; test with controlled payload if authorizedCheck Version:
# Check software version specific to your implementation; consult vendor documentationVerify Fix Applied:
Verify patch version is installed and test that malicious input in keypasswd parameter no longer executes commands📡 Detection & Monitoring
Log Indicators:
- HTTP requests with unusual characters or command syntax in keypasswd parameter
- Unexpected process execution following HTTP requests
Network Indicators:
- HTTP POST/PUT requests to vulnerable endpoints containing shell metacharacters
- Outbound connections from web server to unexpected destinations
SIEM Query:
source="web_logs" AND (keypasswd CONTAINS "|" OR keypasswd CONTAINS ";" OR keypasswd CONTAINS "`" OR keypasswd CONTAINS "$")