CVE-2023-25690
📋 TL;DR
This CVE describes an HTTP request smuggling vulnerability in Apache HTTP Server when mod_proxy is configured with certain RewriteRule or ProxyPassMatch patterns. Attackers can manipulate request data to bypass proxy access controls, forward requests to unintended URLs, or poison caches. Systems running Apache 2.4.0 through 2.4.55 with vulnerable mod_proxy configurations are affected.
💻 Affected Systems
- Apache HTTP Server
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete bypass of proxy security controls allowing attackers to access internal systems, perform cache poisoning attacks, and potentially chain with other vulnerabilities for further exploitation.
Likely Case
Bypass of access restrictions on the proxy server, allowing unauthorized access to backend services or manipulation of cached content.
If Mitigated
Limited impact if proper network segmentation and additional security controls are in place, though the vulnerability still exists.
🎯 Exploit Status
Exploitation requires specific vulnerable configurations but no authentication. Public proof-of-concept code is available.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.4.56
Vendor Advisory: https://httpd.apache.org/security/vulnerabilities_24.html
Restart Required: Yes
Instructions:
1. Download Apache 2.4.56 or later from official sources. 2. Stop Apache service. 3. Backup current configuration. 4. Install updated version. 5. Restart Apache service.
🔧 Temporary Workarounds
Disable vulnerable configurations
allReview and modify RewriteRule and ProxyPassMatch configurations to avoid patterns that match user-supplied URLs and re-insert them via variable substitution.
# Review Apache configuration files for patterns like:
# RewriteRule "^/here/(.*)" "http://example.com:8080/elsewhere?$1" [P]
# Modify or remove vulnerable patterns
Disable mod_proxy if not needed
allIf proxy functionality is not required, disable mod_proxy module entirely.
# Comment out or remove LoadModule proxy_module lines
# In httpd.conf or apache2.conf:
# LoadModule proxy_module modules/mod_proxy.so
🧯 If You Can't Patch
- Implement strict input validation and sanitization for URL parameters in proxy configurations
- Deploy a WAF (Web Application Firewall) with HTTP request smuggling protection rules
🔍 How to Verify
Check if Vulnerable:
Check Apache version and review configuration for mod_proxy with RewriteRule/ProxyPassMatch patterns using variable substitution in URLs.Check Version:
httpd -v or apache2 -vVerify Fix Applied:
Verify Apache version is 2.4.56 or higher and review configuration to ensure vulnerable patterns are removed.📡 Detection & Monitoring
Log Indicators:
- Unusual request patterns with malformed headers
- Requests to unexpected backend URLs
- Cache manipulation attempts
Network Indicators:
- HTTP requests with conflicting Content-Length and Transfer-Encoding headers
- Unusual proxy request patterns
SIEM Query:
source="apache" AND ("Transfer-Encoding" AND "Content-Length") OR "request smuggling"🔗 References
- http://packetstormsecurity.com/files/176334/Apache-2.4.55-mod_proxy-HTTP-Request-Smuggling.html
- https://httpd.apache.org/security/vulnerabilities_24.html
- https://lists.debian.org/debian-lts-announce/2023/04/msg00028.html
- https://security.gentoo.org/glsa/202309-01
- http://packetstormsecurity.com/files/176334/Apache-2.4.55-mod_proxy-HTTP-Request-Smuggling.html
- https://httpd.apache.org/security/vulnerabilities_24.html
- https://lists.debian.org/debian-lts-announce/2023/04/msg00028.html
- https://security.gentoo.org/glsa/202309-01
