CVE-2016-8612 in HTTP Server
Summary
by MITRE
Apache HTTP Server mod_cluster before version httpd 2.4.23 is vulnerable to an Improper Input Validation in the protocol parsing logic in the load balancer resulting in a Segmentation Fault in the serving httpd process.
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Analysis
by VulDB Data Team • 02/17/2023
The vulnerability identified as CVE-2016-8612 affects Apache HTTP Server mod_cluster module versions prior to 2.4.23, representing a critical security flaw in the load balancing component that can lead to denial of service conditions. This issue stems from inadequate input validation within the protocol parsing logic of the load balancer functionality, specifically targeting the communication mechanisms between the load balancer and worker nodes in a clustered environment. The mod_cluster module serves as a crucial component for distributing web traffic across multiple backend servers, making it a prime target for exploitation in distributed denial of service scenarios.
The technical root cause of this vulnerability lies in the improper handling of malformed input data during protocol parsing operations. When the load balancer receives specially crafted input through the mod_cluster communication protocol, the parsing logic fails to properly validate the incoming data structures, leading to memory corruption that ultimately results in a segmentation fault within the httpd process. This segmentation fault causes the affected httpd process to terminate unexpectedly, disrupting service availability for all requests handled by that specific process. The vulnerability manifests during the processing of protocol messages that contain malformed or unexpected data patterns, particularly in the way the load balancer interprets and processes cluster communication packets.
From an operational impact perspective, this vulnerability presents a significant risk to web infrastructure relying on Apache mod_cluster for load distribution. An attacker capable of sending malicious input to the load balancer can trigger process termination, leading to immediate service disruption and potential cascading failures in clustered environments where multiple httpd processes are coordinated. The segmentation fault occurs within the server process itself, making it particularly dangerous as it can be exploited to cause continuous service interruptions without requiring authentication or elevated privileges. The vulnerability affects the availability aspect of the CIA triad, potentially allowing attackers to perform denial of service attacks that can severely impact business operations and user access to web applications.
The vulnerability aligns with CWE-20, which describes improper input validation as a fundamental weakness in software security design, and can be mapped to ATT&CK technique T1499.004 for network denial of service attacks. Organizations utilizing mod_cluster should implement immediate mitigations including upgrading to Apache HTTP Server version 2.4.23 or later, which contains the necessary patches to address the input validation flaws. Additional protective measures include implementing network segmentation to restrict access to the load balancer endpoints, deploying intrusion detection systems to monitor for suspicious protocol traffic patterns, and establishing robust process monitoring to detect and automatically restart terminated httpd processes. The fix implemented in version 2.4.23 involves enhanced input validation routines that properly sanitize and validate all incoming protocol data before processing, preventing the memory corruption that previously led to segmentation faults.