CVE-2015-5887 in Mac OS X
Summary
by MITRE
The TLS Handshake Protocol implementation in Secure Transport in Apple OS X before 10.11 accepts a Certificate Request message within a session in which no Server Key Exchange message has been sent, which allows remote attackers to have an unspecified impact via crafted TLS data.
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Analysis
by VulDB Data Team • 11/21/2024
The vulnerability described in CVE-2015-5887 resides within Apple's Secure Transport implementation in operating systems prior to version 10.11, specifically targeting the TLS Handshake Protocol. This flaw represents a critical deviation from established TLS protocol standards where the system improperly processes certificate requests during resumed sessions. The issue manifests when a Certificate Request message is received without a preceding Server Key Exchange message, creating a scenario that violates fundamental TLS handshake semantics. This improper handling occurs during session resumption, where the cryptographic context should already be established through prior key exchange mechanisms. The vulnerability demonstrates a failure in protocol state validation, allowing attackers to manipulate the handshake sequence in ways that were not anticipated by the protocol design.
The technical exploitation of this vulnerability stems from the improper validation of TLS handshake messages within session resumption contexts. In standard TLS implementations, when a server sends a Certificate Request message, it typically indicates that client authentication is desired, but this message should only appear in contexts where the necessary key exchange information has already been transmitted. The Secure Transport implementation in affected Apple systems fails to properly verify that a Server Key Exchange message has been previously sent before accepting a Certificate Request, creating a potential attack vector. This flaw falls under the category of protocol implementation errors where the system does not correctly enforce the sequence and dependency requirements of TLS handshake messages, making it susceptible to crafted malicious TLS data that can manipulate the authentication flow.
The operational impact of this vulnerability extends beyond simple protocol violations to potentially enable various forms of man-in-the-middle attacks and authentication bypass scenarios. Attackers could leverage this weakness to manipulate certificate validation processes during TLS sessions, potentially allowing them to present fraudulent certificates or interfere with the normal certificate request workflow. The unspecified impact mentioned in the CVE description suggests that the consequences could range from session hijacking to more sophisticated credential manipulation attacks, particularly when combined with other vulnerabilities or attack vectors. This vulnerability particularly affects systems that rely on TLS for secure communications, potentially compromising the integrity of encrypted sessions and the authentication mechanisms that depend on proper certificate handling. The issue is especially concerning in enterprise environments where Apple systems handle sensitive data exchanges and require robust TLS security implementations.
Mitigation strategies for CVE-2015-5887 primarily involve upgrading affected Apple operating systems to version 10.11 or later, where the Secure Transport implementation has been corrected to properly validate TLS handshake message sequences. System administrators should also implement network monitoring to detect anomalous TLS handshake patterns that might indicate exploitation attempts, particularly focusing on certificate request messages received without appropriate key exchange information. Organizations should review their TLS configurations and ensure that certificate validation procedures are properly enforced, including implementing proper certificate pinning where appropriate. This vulnerability aligns with CWE-295 which addresses improper certificate validation and relates to ATT&CK technique T1552.001 for credentials from password storage, as the compromised handshake process could potentially lead to credential exposure during authentication. Network security teams should also consider implementing intrusion detection systems that can identify and alert on malformed TLS handshake sequences that match the patterns associated with this vulnerability.