CVE-2014-3616 in nginx
Summary
by MITRE
nginx 0.5.6 through 1.7.4, when using the same shared ssl_session_cache or ssl_session_ticket_key for multiple servers, can reuse a cached SSL session for an unrelated context, which allows remote attackers with certain privileges to conduct "virtual host confusion" attacks.
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Analysis
by VulDB Data Team • 02/20/2022
The vulnerability identified as CVE-2014-3616 affects nginx versions ranging from 0.5.6 through 1.7.4 and represents a critical security flaw in the handling of SSL session caching mechanisms. This issue stems from the improper management of shared SSL session caches and session ticket keys across multiple server configurations, creating a scenario where security contexts can be confused and exploited by malicious actors. The vulnerability specifically impacts systems that utilize shared SSL session caches or session ticket keys for multiple virtual hosts within the same nginx instance.
The technical root cause of this vulnerability lies in the design flaw where nginx fails to properly validate the relationship between cached SSL sessions and the specific server contexts they were originally established for. When multiple servers share the same ssl_session_cache or ssl_session_ticket_key directives, the SSL session resumption mechanism does not adequately verify that the session being reused belongs to the same virtual host or context as the current connection attempt. This allows an attacker to potentially reuse a cached session from one virtual host to establish a connection to another unrelated virtual host, effectively bypassing the intended security boundaries between different server contexts.
From an operational perspective, this vulnerability enables what is known as a "virtual host confusion" attack pattern that aligns with tactics described in the MITRE ATT&CK framework under the technique of credential access through session hijacking. The impact is significant as it can allow attackers to impersonate legitimate users or gain unauthorized access to resources that should be isolated between different virtual hosts. The vulnerability is particularly dangerous in environments where multiple applications or customers are hosted on the same nginx instance, as it undermines the fundamental security principle of isolation between different virtual server contexts.
The security implications extend beyond simple session reuse to encompass potential data leakage, unauthorized access to sensitive information, and the ability to conduct man-in-the-middle attacks across different virtual host boundaries. This flaw can be exploited by remote attackers who have the capability to establish SSL connections and observe session caching behavior, making it particularly concerning for web applications that rely on SSL/TLS for security. The vulnerability is classified under CWE-200, which deals with information exposure, and represents a specific instance of improper access control in cryptographic systems.
Mitigation strategies for CVE-2014-3616 require immediate action to address the root cause of shared session caching across virtual hosts. The primary recommendation is to ensure that each virtual host maintains its own dedicated ssl_session_cache and ssl_session_ticket_key directives, preventing the sharing of session state between different server contexts. Administrators should implement separate session cache configurations for each virtual host or application, and consider using unique session ticket keys for different server blocks. Additionally, upgrading to nginx versions beyond 1.7.4 resolves this vulnerability, as the developers implemented proper session validation mechanisms to prevent cross-context session reuse. Network administrators should also consider implementing additional monitoring to detect unusual session reuse patterns and establish proper logging of SSL session activities to identify potential exploitation attempts.