CVE-2024-38477 Overview
CVE-2024-38477 is a null pointer dereference vulnerability affecting the mod_proxy module in Apache HTTP Server versions 2.4.59 and earlier. This vulnerability allows a remote attacker to crash the server by sending a specially crafted malicious request, resulting in a denial of service condition.
The flaw resides in how mod_proxy handles certain proxy requests. When processing these requests, the module fails to properly validate pointer references before dereferencing them, leading to a null pointer access that terminates the server process.
Critical Impact
Remote attackers can cause a complete denial of service by crashing Apache HTTP Server instances through malicious requests targeting the mod_proxy module, potentially disrupting web services for all users.
Affected Products
- Apache HTTP Server versions up to and including 2.4.59
- NetApp Clustered Data ONTAP 9.0
- Systems utilizing mod_proxy for reverse proxy, load balancing, or gateway configurations
Discovery Timeline
- 2024-07-01 - CVE-2024-38477 published to NVD
- 2025-11-03 - Last updated in NVD database
Technical Details for CVE-2024-38477
Vulnerability Analysis
The vulnerability exists within the mod_proxy module, a critical component of Apache HTTP Server used for proxying HTTP requests. The null pointer dereference occurs when the proxy module processes certain malformed or specially crafted requests that trigger an unexpected code path where a pointer is accessed without proper null validation.
When exploited, this vulnerability causes an immediate crash of the Apache HTTP Server worker process handling the request. Depending on the server configuration and the Multi-Processing Module (MPM) in use, this could result in temporary service disruption or require manual intervention to restore service availability.
The vulnerability is accessible over the network without requiring authentication or user interaction, making it particularly concerning for publicly exposed Apache servers with mod_proxy enabled.
Root Cause
The root cause is a missing null pointer check in the mod_proxy module's request handling logic. When certain conditions are met during proxy request processing, the code attempts to dereference a pointer that may be null, resulting in a segmentation fault and process termination. This represents a classic CWE-476 (NULL Pointer Dereference) vulnerability pattern.
Attack Vector
The attack vector is network-based and requires no privileges or user interaction. An attacker can send a crafted HTTP request to a vulnerable Apache server with mod_proxy enabled. The request exploits the null pointer dereference condition in the proxy module, causing the server process to crash.
The attack characteristics include:
- Network accessible: Can be exploited remotely over HTTP/HTTPS
- No authentication required: The attack works against unauthenticated endpoints
- No user interaction: Exploitation is fully automated
- Availability impact: Complete denial of service for the affected server process
Detection Methods for CVE-2024-38477
Indicators of Compromise
- Unexpected Apache HTTP Server process crashes or restarts in system logs
- Segmentation fault entries in Apache error logs related to mod_proxy
- Increased frequency of child process spawning by the Apache parent process
- Core dump files generated by crashed Apache worker processes
Detection Strategies
- Monitor Apache error logs for segmentation fault signals (SIGSEGV) associated with proxy operations
- Implement web application firewall (WAF) rules to detect anomalous proxy request patterns
- Deploy intrusion detection system (IDS) signatures targeting malformed proxy requests
- Set up automated alerts for unexpected Apache service restarts or crashes
Monitoring Recommendations
- Configure centralized logging for all Apache HTTP Server instances to correlate crash events
- Enable core dump generation in controlled environments to facilitate forensic analysis of crashes
- Monitor server uptime metrics and establish baselines to detect denial of service attempts
- Implement health checks for proxy endpoints to rapidly detect service disruption
How to Mitigate CVE-2024-38477
Immediate Actions Required
- Upgrade Apache HTTP Server to version 2.4.60 or later, which contains the fix for this vulnerability
- If immediate patching is not possible, consider temporarily disabling mod_proxy if it is not essential for operations
- Implement rate limiting and request filtering at the network perimeter to reduce exposure
- Review and restrict access to proxy endpoints using IP allowlists where applicable
Patch Information
Apache Software Foundation has released version 2.4.60 which addresses this vulnerability. Users are strongly recommended to upgrade to this version or later. The official security advisory is available at the Apache HTTP Server Vulnerabilities page.
Additional vendor advisories:
Workarounds
- Disable mod_proxy and related modules (mod_proxy_http, mod_proxy_ajp, etc.) if proxy functionality is not required
- Implement a reverse proxy or load balancer in front of Apache to filter potentially malicious requests
- Use a Web Application Firewall (WAF) to inspect and block suspicious proxy requests
- Restrict access to proxy functionality to trusted networks or authenticated users only
# Disable mod_proxy in Apache configuration (Debian/Ubuntu)
sudo a2dismod proxy proxy_http proxy_ajp proxy_balancer
sudo systemctl restart apache2
# For RedHat/CentOS, comment out LoadModule directives in httpd.conf
# LoadModule proxy_module modules/mod_proxy.so
# LoadModule proxy_http_module modules/mod_proxy_http.so
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
