CVE-2021-21909
📋 TL;DR
CVE-2021-21909 is a path traversal vulnerability in a file deletion command that allows arbitrary file deletion via specially crafted arguments. Attackers can delete critical system files by manipulating command inputs. This affects systems running vulnerable versions of the affected software.
💻 Affected Systems
- Specific software name not provided in CVE description
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise through deletion of critical OS files, leading to system instability, data loss, or denial of service.
Likely Case
Unauthorized deletion of application or user data, causing service disruption and potential data integrity issues.
If Mitigated
Limited impact with proper input validation and file permission restrictions in place.
🎯 Exploit Status
Exploitation requires ability to pass arguments to the vulnerable command, which typically requires some level of access.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check vendor advisory for specific patched version
Vendor Advisory: https://talosintelligence.com/vulnerability_reports/TALOS-2021-1359
Restart Required: Yes
Instructions:
1. Identify affected software version
2. Apply vendor-provided patch
3. Restart affected services
4. Verify patch application
🔧 Temporary Workarounds
Input Validation
allImplement strict input validation to prevent path traversal characters in command arguments
Implement input sanitization in code: reject arguments containing '../', '..\', or absolute paths
File Permission Restrictions
linuxRun application with minimal file system permissions
chmod 750 /path/to/application
setfacl -m u:appuser:rx /path/to/restricted
🧯 If You Can't Patch
- Implement strict access controls to limit who can execute the vulnerable command
- Monitor file deletion activities and implement alerting for suspicious patterns
🔍 How to Verify
Check if Vulnerable:
Test if the file deletion command accepts path traversal sequences like '../../etc/passwd' in argumentsCheck Version:
Check software version using vendor-specific command (e.g., software --version)Verify Fix Applied:
Verify that path traversal attempts are rejected and proper input validation is in place📡 Detection & Monitoring
Log Indicators:
- Unusual file deletion patterns
- Commands with path traversal sequences
- Failed file deletion attempts with suspicious paths
Network Indicators:
- N/A - Local command execution vulnerability
SIEM Query:
source="application.log" AND ("..\" OR "../") AND ("delete" OR "del" OR "rm")