CVE-2021-20517
📋 TL;DR
This vulnerability in IBM WebSphere Application Server Network Deployment allows authenticated remote attackers to perform directory traversal attacks using specially crafted URLs containing 'dot dot' sequences (/../). Attackers can read and delete arbitrary files on the system. Affects versions 8.5 and 9.0 of IBM WebSphere Application Server Network Deployment.
💻 Affected Systems
- IBM WebSphere Application Server Network Deployment
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise through reading sensitive files (passwords, keys, configuration) and deleting critical system files causing service disruption or system failure.
Likely Case
Data exfiltration of sensitive application data, configuration files, or credentials stored on the server filesystem.
If Mitigated
Limited impact if proper file permissions and access controls restrict what authenticated users can access.
🎯 Exploit Status
Directory traversal is a well-understood attack pattern. Requires authenticated access but is trivial to exploit once authenticated.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Apply Interim Fix PI99821 or later cumulative fix
Vendor Advisory: https://www.ibm.com/support/pages/node/6456955
Restart Required: Yes
Instructions:
1. Download the appropriate interim fix from IBM Fix Central. 2. Stop all WebSphere servers. 3. Apply the fix using IBM Installation Manager. 4. Restart all WebSphere servers. 5. Verify the fix is applied.
🔧 Temporary Workarounds
Restrict URL patterns
allConfigure web server or application firewall to block URLs containing directory traversal sequences
Implement strict file permissions
allRestrict file system permissions to limit what the WebSphere process can access
🧯 If You Can't Patch
- Implement network segmentation to restrict access to WebSphere servers
- Deploy web application firewall with directory traversal protection rules
🔍 How to Verify
Check if Vulnerable:
Check WebSphere version via administrative console or versionInfo.sh scriptCheck Version:
./versionInfo.sh (on Linux/Unix) or versionInfo.bat (on Windows)Verify Fix Applied:
Verify interim fix PI99821 or later is installed via IBM Installation Manager or versionInfo.sh📡 Detection & Monitoring
Log Indicators:
- URL requests containing /../ patterns in access logs
- Unauthorized file access attempts in system logs
Network Indicators:
- HTTP requests with encoded directory traversal sequences (%2e%2e%2f, ..%2f)
SIEM Query:
source="websphere_access.log" AND (url="*../*" OR url="*..%2f*")