CVE-2023-25690: Apache HTTP Server Auth Bypass Vulnerability

CVE-2023-25690 Overview

Some mod_proxy configurations on Apache HTTP Server versions 2.4.0 through 2.4.55 allow an HTTP Request Smuggling attack, which can result in bypassing access controls and cache poisoning.

Critical Impact
This vulnerability could allow attackers to proxy unintended URLs to existing origin servers and execute cache poisoning.

Affected Products

Apache HTTP Server versions 2.4.0 through 2.4.55

Discovery Timeline

2023-03-07 - CVE-2023-25690 published to NVD
2025-02-13 - Last updated in NVD database

Technical Details for CVE-2023-25690

Vulnerability Analysis

This vulnerability arises when mod_proxy is used along with RewriteRule or ProxyPassMatch, where a non-specific pattern in the user-request is re-inserted into the proxied request-target. This can be exploited to perform HTTP Request Smuggling, allowing attackers to bypass security controls and potentially poison caches.

Root Cause

The root cause involves improper handling of user-supplied request-target data when utilizing RewriteRule directives with variable substitution.

Attack Vector

Network-based attack vector leveraging crafted HTTP requests.

python

# Example exploitation code (sanitized)
import requests

payload = "GET / HTTP/1.1\r\nHost: vulnerable.server\r\nContent-Length: 0\r\n\r\nGET /malicious HTTP/1.1\r\nHost: target.server\r\n\r\n"

response = requests.post("http://vulnerable.server", data=payload)

Detection Methods for CVE-2023-25690

Indicators of Compromise

Unexpected log entries indicating malformed requests
Anomalous proxy behavior or bypasses

Detection Strategies

Monitoring of HTTP traffic for request smuggling patterns using IDS/IPS systems. Configure WAFs to detect and block malformed HTTP requests.

Monitoring Recommendations

Enhanced logging of HTTP headers combined with anomaly detection on access patterns may help identify exploitation attempts.

How to Mitigate CVE-2023-25690

Immediate Actions Required

Disable vulnerable mod_proxy configurations temporarily
Apply strict input validation on headers

Patch Information

Upgrade to Apache HTTP Server version 2.4.56 or higher to eliminate the vulnerability.

Workarounds

Insert strict input validation rules in mod_rewrite configurations to prevent unintended URL manipulations.

bash

# Configuration example
RewriteRule "^/here/(.*)" "http://example.com/securepath?$1" [P,L]
ProxyPassReverse /here/ http://example.com/securepath/