CVE-2016-5419 in macOS
Summary
by MITRE
curl and libcurl before 7.50.1 do not prevent TLS session resumption when the client certificate has changed, which allows remote attackers to bypass intended restrictions by resuming a session.
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Analysis
by VulDB Data Team • 10/07/2022
The vulnerability identified as CVE-2016-5419 affects curl and libcurl versions prior to 7.50.1, representing a critical flaw in the transport layer security implementation that undermines session management protocols. This issue specifically targets the TLS session resumption mechanism, which is designed to improve performance by allowing clients and servers to reuse previously established session parameters without repeating the full handshake process. The vulnerability arises when a client certificate changes between sessions yet the system still permits session resumption, creating a security gap that can be exploited by malicious actors.
The technical flaw stems from improper validation of client certificate consistency during TLS session resumption processes. When a client presents a new certificate while attempting to resume a previous TLS session, the affected versions of curl and libcurl fail to verify that the certificate matches the one used in the original session. This oversight allows attackers to potentially bypass authentication mechanisms and access restricted resources by leveraging a cached session that was originally established with different credentials. The vulnerability operates at the application layer protocol level and specifically impacts the TLS implementation within the curl library ecosystem.
From an operational standpoint, this vulnerability presents significant risks to organizations relying on curl for secure communications, particularly in environments where client certificate authentication is employed. Attackers can exploit this weakness to maintain unauthorized access to services, potentially bypassing access controls that depend on certificate-based authentication. The impact extends beyond simple privilege escalation to include potential data exfiltration, service disruption, and unauthorized system access. The vulnerability is particularly concerning in scenarios where session resumption is enabled by default or where administrators have not explicitly disabled this feature, as it can be leveraged without requiring additional privileges or complex attack vectors.
Organizations should immediately upgrade to curl and libcurl version 7.50.1 or later to remediate this vulnerability, as the fix implements proper certificate validation during session resumption. Additional mitigations include disabling TLS session resumption when client certificate authentication is in use, implementing proper certificate lifecycle management, and monitoring for suspicious session resumption attempts. This vulnerability aligns with CWE-319, which addresses the exposure of sensitive information through improper session management, and maps to ATT&CK technique T1552.001, which covers unsecured credentials through improper certificate validation. Security teams should also consider implementing network monitoring to detect anomalous session resumption patterns that may indicate exploitation attempts. The vulnerability demonstrates the importance of comprehensive protocol validation and the need for robust certificate management practices in maintaining secure communications infrastructure.