CVE-2017-7659 in macOS
Summary
by MITRE
A maliciously constructed HTTP/2 request could cause mod_http2 2.4.24, 2.4.25 to dereference a NULL pointer and crash the server process.
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Analysis
by VulDB Data Team • 01/21/2021
The vulnerability identified as CVE-2017-7659 represents a critical NULL pointer dereference flaw within the mod_http2 module of the Apache HTTP Server. This issue affects versions 2.4.24 and 2.4.25, where specifically crafted HTTP/2 requests can trigger unexpected behavior leading to server process termination. The vulnerability stems from inadequate input validation and error handling within the HTTP/2 protocol implementation, creating a condition where the module attempts to access memory locations that have not been properly initialized or allocated.
The technical exploitation of this vulnerability occurs when an attacker sends a malformed HTTP/2 frame that causes the mod_http2 module to process a NULL pointer reference. This typically happens during the parsing or handling of specific HTTP/2 headers or frames that contain unexpected or malformed data structures. The flaw manifests as a segmentation fault or similar memory access violation, causing the Apache server process to crash and terminate abruptly. This type of vulnerability falls under CWE-476 which specifically addresses NULL pointer dereference conditions, making it particularly dangerous as it can be exploited to cause denial of service attacks against web servers.
From an operational perspective, this vulnerability presents a significant risk to web server availability and reliability. When exploited successfully, the vulnerability allows attackers to perform denial of service attacks by simply sending malicious HTTP/2 requests to the affected server. The impact extends beyond simple service disruption as it can potentially be used as a stepping stone for more sophisticated attacks or to overwhelm server resources through repeated exploitation attempts. The vulnerability is particularly concerning in environments where HTTP/2 is actively used, as it requires no authentication or elevated privileges to exploit, making it accessible to anyone who can send HTTP/2 requests to the target server.
The mitigation strategy for CVE-2017-7659 involves immediate deployment of patches provided by the Apache Software Foundation, specifically upgrading to Apache HTTP Server versions that contain the fix for this NULL pointer dereference issue. Organizations should also consider implementing network-level protections such as rate limiting and request filtering to reduce the impact of potential exploitation attempts. Additionally, security monitoring should be enhanced to detect unusual patterns of HTTP/2 traffic that may indicate exploitation attempts. The vulnerability aligns with ATT&CK technique T1499.004 which covers network denial of service attacks, and organizations should consider implementing defensive measures that address this specific attack vector within their broader security frameworks. System administrators should also review their HTTP/2 configuration settings and ensure that appropriate logging and alerting mechanisms are in place to detect potential exploitation attempts.