CVE-2015-0253 in HTTP Server
Summary
by MITRE
The read_request_line function in server/protocol.c in the Apache HTTP Server 2.4.12 does not initialize the protocol structure member, which allows remote attackers to cause a denial of service (NULL pointer dereference and process crash) by sending a request that lacks a method to an installation that enables the INCLUDES filter and has an ErrorDocument 400 directive specifying a local URI.
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Analysis
by VulDB Data Team • 06/03/2022
The vulnerability described in CVE-2015-0253 resides within the Apache HTTP Server version 2.4.12 where the read_request_line function in server/protocol.c fails to properly initialize a protocol structure member. This flaw manifests when the server processes incoming HTTP requests that lack a proper method specification, creating a condition that can be exploited by remote attackers to execute a denial of service attack. The vulnerability specifically impacts installations that have the INCLUDES filter enabled and where an ErrorDocument 400 directive is configured to reference a local URI, creating a dangerous combination that leads to system instability.
The technical root cause of this vulnerability stems from inadequate input validation and memory management within the HTTP server's request processing pipeline. When the server encounters a malformed request without a method identifier, the protocol structure member remains uninitialized, leading to a NULL pointer dereference during subsequent processing operations. This particular flaw represents a classic example of improper initialization in software development, which is categorized under CWE-457: Use of Uninitialized Variable. The absence of proper null checking and initialization mechanisms in the protocol structure creates an exploitable condition where malicious actors can craft specific requests to trigger the undefined behavior.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise the entire server availability. Remote attackers can exploit this weakness by sending carefully crafted HTTP requests that lack method specifications, causing the Apache HTTP Server process to crash and terminate unexpectedly. This denial of service condition can be particularly damaging in production environments where server uptime is critical for business operations. The vulnerability affects the server's ability to handle error conditions gracefully, as the system fails to properly process malformed requests and instead crashes due to the uninitialized memory access. This behavior aligns with ATT&CK technique T1499.004: Endpoint Denial of Service, where adversaries target application-level vulnerabilities to disrupt service availability.
The exploitation scenario requires specific server configuration conditions to be effective, namely the activation of the INCLUDES filter and the presence of an ErrorDocument 400 directive referencing a local URI. This configuration dependency means that not all Apache installations are vulnerable, but those meeting these criteria face a significant risk of service interruption. The vulnerability demonstrates how seemingly minor initialization flaws can have major operational consequences, particularly when combined with specific module configurations. Organizations using Apache HTTP Server 2.4.12 should immediately consider upgrading to patched versions or implementing workarounds to prevent exploitation. The recommended mitigation strategy includes updating to Apache HTTP Server version 2.4.13 or later, which contains the necessary fixes to properly initialize the protocol structure member and prevent the NULL pointer dereference condition. Additionally, administrators should review their server configurations to ensure that ErrorDocument directives are properly configured and that unnecessary modules are disabled to minimize attack surface. This vulnerability serves as a reminder of the critical importance of proper memory management and input validation in server applications, particularly those handling network traffic from untrusted sources.