CVE-2019-0190 in Essbase
Summary
by MITRE
A bug exists in the way mod_ssl handled client renegotiations. A remote attacker could send a carefully crafted request that would cause mod_ssl to enter a loop leading to a denial of service. This bug can be only triggered with Apache HTTP Server version 2.4.37 when using OpenSSL version 1.1.1 or later, due to an interaction in changes to handling of renegotiation attempts.
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Analysis
by VulDB Data Team • 07/14/2024
The vulnerability identified as CVE-2019-0190 represents a critical denial of service flaw within the Apache HTTP Server's mod_ssl module that specifically affects certain configurations involving OpenSSL 1.1.1 and later versions. This issue stems from improper handling of client renegotiation attempts within the SSL/TLS protocol implementation, creating a condition where malicious actors can exploit the server's response to crafted requests. The vulnerability operates through a specific interaction between Apache's mod_ssl module and OpenSSL's renegotiation handling mechanisms, making it particularly challenging to address without understanding the underlying protocol complexities.
The technical flaw manifests when mod_ssl encounters client renegotiation requests in Apache 2.4.37 running on systems with OpenSSL 1.1.1 or newer versions. The module fails to properly validate or handle the renegotiation process, causing it to enter an infinite loop or excessive resource consumption when processing malformed or specially crafted renegotiation requests. This behavior occurs because the SSL implementation does not adequately check the validity of renegotiation attempts or properly terminate the renegotiation process when encountering unexpected conditions. The flaw essentially creates a resource exhaustion scenario where the server becomes unresponsive to legitimate requests while continuously processing the malicious renegotiation attempts. According to CWE classification, this vulnerability maps to CWE-400: Uncontrolled Resource Consumption, as it allows an attacker to consume server resources indefinitely through crafted requests. The issue also relates to CWE-399: Resource Management Errors, given the improper handling of SSL renegotiation resources.
The operational impact of this vulnerability extends beyond simple service disruption, as it can effectively render Apache servers unusable to legitimate users while consuming significant system resources. Attackers can trigger this condition with minimal network traffic, making it particularly dangerous in production environments where server availability is critical. The vulnerability affects systems that are actively using SSL/TLS connections and have configured mod_ssl with OpenSSL 1.1.1 or later, creating a narrow but significant attack surface. In enterprise environments, this could lead to complete service outages, impacting business operations and potentially resulting in financial losses. The DoS condition can persist until the server is manually restarted or the specific renegotiation request is processed, making it difficult to mitigate without proper monitoring and immediate response procedures. From an ATT&CK framework perspective, this vulnerability aligns with T1499.004: Endpoint Denial of Service, as it targets endpoint availability through resource exhaustion techniques.
Mitigation strategies for CVE-2019-0190 primarily involve updating the affected Apache HTTP Server and OpenSSL components to versions that address the renegotiation handling issue. The most effective solution is to upgrade to Apache HTTP Server 2.4.38 or later, which includes fixes for the renegotiation loop condition. Additionally, system administrators should consider implementing rate limiting or connection throttling mechanisms to reduce the impact of potential attacks. Configuration changes such as disabling SSL renegotiation entirely can also provide protection, though this may impact legitimate use cases where renegotiation is required. Network-level protections including firewalls and intrusion detection systems can help identify and block malicious renegotiation attempts before they reach the vulnerable server. Organizations should also implement monitoring solutions that can detect unusual resource consumption patterns or excessive SSL connection attempts that might indicate exploitation attempts. The vulnerability highlights the importance of keeping cryptographic libraries and web server software up to date, as the issue was resolved through proper handling of renegotiation protocol states in subsequent releases. Security teams should conduct regular vulnerability assessments to identify systems running affected configurations and ensure that patches are applied promptly to maintain operational continuity and security posture.