CVE-2017-3169 in macOS
Summary
by MITRE
In Apache httpd 2.2.x before 2.2.33 and 2.4.x before 2.4.26, mod_ssl may dereference a NULL pointer when third-party modules call ap_hook_process_connection() during an HTTP request to an HTTPS port.
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Analysis
by VulDB Data Team • 01/21/2021
The vulnerability identified as CVE-2017-3169 represents a critical NULL pointer dereference flaw within the Apache HTTP Server's mod_ssl module. This issue affects versions prior to 2.2.33 and 2.4.26 across the 2.2.x and 2.4.x release branches respectively. The flaw manifests when third-party modules invoke the ap_hook_process_connection() function during HTTP requests processed through HTTPS ports, creating a scenario where the mod_ssl module attempts to access memory at a null address. This condition occurs due to insufficient validation of connection state variables within the SSL processing pipeline, particularly when handling concurrent requests on secure ports.
From a technical perspective, the vulnerability stems from improper handling of connection context within the Apache server's module architecture. When mod_ssl processes an HTTPS request, it expects certain connection structures to be properly initialized before accessing their members. However, when third-party modules register hooks through ap_hook_process_connection() during the request lifecycle, they may trigger processing at a point where the SSL connection context remains uninitialized or has been prematurely deallocated. This creates a race condition scenario where the module attempts to dereference a pointer that contains a null value, leading to an immediate server crash or potential memory corruption. The flaw aligns with CWE-476 which specifically addresses NULL pointer dereference vulnerabilities in software systems.
The operational impact of this vulnerability extends beyond simple service disruption, as it provides potential attackers with a means to execute denial-of-service attacks against Apache HTTP Server instances. An attacker could craft malicious requests that specifically target the vulnerable code path, causing the web server to crash repeatedly and making the service unavailable to legitimate users. In environments where Apache serves critical web applications or handles high volumes of HTTPS traffic, such an attack could result in significant business disruption. The vulnerability also raises concerns about potential privilege escalation or information disclosure if the crash conditions can be manipulated to trigger memory corruption that might be exploitable by malicious actors. This aligns with ATT&CK technique T1499 which covers network denial of service attacks targeting web servers.
Mitigation strategies for CVE-2017-3169 primarily focus on immediate version upgrades to patched releases of Apache HTTP Server. Organizations should prioritize updating to Apache 2.2.33 or 2.4.26 respectively, as these versions contain the necessary code modifications to properly validate connection context before attempting to access SSL-related structures. Additionally, administrators should review third-party module configurations to identify any modules that might be invoking ap_hook_process_connection() during SSL request processing and consider temporarily disabling such modules until proper compatibility can be verified. Network-level protections such as rate limiting and intrusion detection systems can provide additional defense-in-depth measures, though they do not address the root cause of the vulnerability. The fix implemented in patched versions typically involves adding null pointer checks and proper initialization validation within the mod_ssl module's connection processing logic, ensuring that all required context variables are properly established before any memory access operations occur.