CVE-2025-53020 Overview
CVE-2025-53020 is a Memory Leak vulnerability in Apache HTTP Server that allows attackers to cause a denial of service condition through improper memory management. The vulnerability exists due to late release of memory after its effective lifetime, classified under CWE-401 (Missing Release of Memory after Effective Lifetime).
This memory management flaw affects Apache HTTP Server versions from 2.4.17 up to 2.4.63. When exploited, an attacker can cause the server to consume excessive memory resources, potentially leading to service degradation or complete denial of service for legitimate users.
Critical Impact
Network-accessible Apache HTTP Server instances can be targeted to exhaust system memory, causing service unavailability without requiring authentication or user interaction.
Affected Products
- Apache HTTP Server versions 2.4.17 through 2.4.63
Discovery Timeline
- 2025-07-10 - CVE-2025-53020 published to NVD
- 2025-11-04 - Last updated in NVD database
Technical Details for CVE-2025-53020
Vulnerability Analysis
This vulnerability stems from improper memory lifecycle management within Apache HTTP Server. Memory allocated during request processing is not released in a timely manner after it is no longer needed, leading to gradual memory accumulation over time.
The flaw can be exploited remotely over the network without requiring any privileges or user interaction. When an attacker sends specially crafted requests to a vulnerable Apache HTTP Server instance, the server fails to properly deallocate memory resources, causing progressive memory exhaustion.
The primary impact of this vulnerability is availability degradation. As memory consumption grows unchecked, the server's ability to handle legitimate requests diminishes, eventually leading to service disruption or complete system unavailability.
Root Cause
The root cause is a CWE-401 (Missing Release of Memory after Effective Lifetime) weakness. Memory that is allocated during certain operations within Apache HTTP Server is not properly freed after it is no longer required. This results in a memory leak condition where memory resources are held beyond their useful lifetime, accumulating with each request processed by the server.
Attack Vector
The attack can be executed remotely over the network without authentication. An attacker can send requests to the vulnerable Apache HTTP Server, triggering the memory leak condition. By repeatedly sending such requests, the attacker can accelerate memory exhaustion, leading to denial of service.
The vulnerability mechanism involves the server's failure to properly release memory allocations after request processing completes. Technical details about the specific code paths involved can be found in the Apache HTTPD Security Advisory and the Openwall OSS-Security discussion.
Detection Methods for CVE-2025-53020
Indicators of Compromise
- Gradual increase in memory consumption by Apache HTTP Server processes over time
- Server performance degradation without corresponding increase in legitimate traffic
- Apache worker processes consuming abnormally high amounts of memory
- System-level out-of-memory events or OOM killer activation affecting httpd processes
Detection Strategies
- Monitor Apache HTTP Server process memory usage for unusual growth patterns using system monitoring tools
- Implement alerting for memory consumption thresholds on web server hosts
- Review server logs for signs of potential exploitation attempts or unusual request patterns
- Deploy application performance monitoring (APM) solutions to track memory allocation trends
Monitoring Recommendations
- Configure continuous memory usage monitoring for all Apache HTTP Server processes
- Set up automated alerts when memory consumption exceeds baseline thresholds
- Implement periodic service health checks to detect availability degradation
- Review and correlate access logs with memory consumption spikes to identify potential attack patterns
How to Mitigate CVE-2025-53020
Immediate Actions Required
- Upgrade Apache HTTP Server to version 2.4.64 or later immediately
- Review current Apache HTTP Server version across all deployments using httpd -v or apache2 -v
- Implement memory monitoring and alerting for Apache processes as an interim measure
- Consider implementing rate limiting to reduce potential exploitation impact
Patch Information
Apache has released version 2.4.64 which addresses this vulnerability. Users running Apache HTTP Server versions 2.4.17 through 2.4.63 are strongly recommended to upgrade immediately. The official patch information and security advisory is available at the Apache HTTPD Security Vulnerabilities page.
Debian users should also review the Debian LTS Security Announcement for distribution-specific guidance.
Workarounds
- Implement resource limits using ulimit or cgroup configurations to cap memory usage per Apache process
- Configure periodic automatic restarts of Apache HTTP Server to clear accumulated memory
- Deploy load balancers or reverse proxies with connection rate limiting to reduce attack surface
- Monitor memory consumption closely and restart services proactively when thresholds are approached
# Example: Configure memory limits using systemd for Apache
sudo systemctl edit apache2
# Add the following in the override file:
# [Service]
# MemoryMax=2G
# MemoryHigh=1.5G
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
