CVE-2024-38474
📋 TL;DR
A substitution encoding vulnerability in Apache HTTP Server's mod_rewrite module allows attackers to bypass security restrictions and execute scripts in directories that should be protected. This affects Apache HTTP Server versions 2.4.59 and earlier. Attackers can potentially execute arbitrary code or access sensitive files that should only be accessible via CGI execution.
💻 Affected Systems
- Apache HTTP Server
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise, data theft, and lateral movement within the network.
Likely Case
Unauthorized script execution leading to information disclosure, privilege escalation, or limited code execution within web server context.
If Mitigated
Limited impact due to proper input validation, minimal mod_rewrite usage, and restricted directory permissions.
🎯 Exploit Status
Exploitation requires specific mod_rewrite configurations and understanding of substitution encoding issues. No public exploit code has been identified at this time.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.4.60
Vendor Advisory: https://httpd.apache.org/security/vulnerabilities_24.html
Restart Required: Yes
Instructions:
1. Download Apache HTTP Server 2.4.60 from official Apache mirrors. 2. Stop the Apache service. 3. Backup current configuration files. 4. Install the new version following platform-specific installation procedures. 5. Restore configuration files. 6. Start the Apache service. 7. Test functionality.
🔧 Temporary Workarounds
Disable problematic RewriteRules
allIdentify and disable or modify RewriteRules that capture and substitute unsafely. Add the 'UnsafeAllow3F' flag to rules that require unsafe substitution.
# Review .htaccess and httpd.conf files for RewriteRule directives
# Add [UnsafeAllow3F] flag to rules requiring unsafe substitution
# Example: RewriteRule ^pattern$ substitution [UnsafeAllow3F]
Restrict mod_rewrite usage
allDisable mod_rewrite module if not required for critical functionality.
# Comment out or remove LoadModule rewrite_module modules/mod_rewrite.so in httpd.conf
# Restart Apache after changes
🧯 If You Can't Patch
- Implement strict input validation and sanitization for all mod_rewrite substitutions
- Apply network segmentation and restrict Apache server access to trusted networks only
🔍 How to Verify
Check if Vulnerable:
Check Apache version with 'httpd -v' or 'apache2 -v' and verify if it's 2.4.59 or earlier. Review mod_rewrite configuration for unsafe substitution patterns.Check Version:
httpd -v # or apache2 -v depending on installationVerify Fix Applied:
Verify Apache version is 2.4.60 or later. Test previously vulnerable RewriteRules to ensure they either work correctly with UnsafeAllow3F flag or fail safely.📡 Detection & Monitoring
Log Indicators:
- Unusual access patterns to protected directories
- Failed CGI execution attempts
- mod_rewrite rule processing errors
- Access to scripts outside expected URL paths
Network Indicators:
- HTTP requests with unusual encoding patterns
- Requests attempting to bypass directory restrictions
- Unexpected script execution patterns
SIEM Query:
source="apache_access" AND (uri="/cgi-bin/*" OR uri="*.cgi" OR uri="*.pl") AND status=200 | stats count by src_ip, uri