CVE-2015-3197 in Enterprise Session Border Controller
Summary
by MITRE
ssl/s2_srvr.c in OpenSSL 1.0.1 before 1.0.1r and 1.0.2 before 1.0.2f does not prevent use of disabled ciphers, which makes it easier for man-in-the-middle attackers to defeat cryptographic protection mechanisms by performing computations on SSLv2 traffic, related to the get_client_master_key and get_client_hello functions.
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Analysis
by VulDB Data Team • 09/27/2022
The vulnerability described in CVE-2015-3197 represents a critical flaw in OpenSSL's SSLv2 protocol implementation that fundamentally undermines cryptographic security assurances. This issue affects OpenSSL versions prior to 1.0.1r and 1.0.2f, where the ssl/s2_srvr.c module fails to properly enforce cipher suite restrictions. The flaw specifically resides in the get_client_master_key and get_client_hello functions that handle SSLv2 client negotiations, creating a scenario where disabled cipher suites can still be utilized during cryptographic handshakes. This represents a direct violation of security policy enforcement mechanisms that should prevent the use of known weak or compromised cryptographic algorithms.
The technical nature of this vulnerability stems from improper validation of cipher suite availability during SSLv2 protocol processing. When OpenSSL processes SSLv2 client hello messages, it should verify that the requested cipher suites are enabled and considered secure according to the server's cryptographic policy. However, the implementation fails to perform this critical validation, allowing attackers to specify disabled ciphers in their handshake requests. This behavior creates a pathway for attackers to force the use of weaker cryptographic mechanisms that may have been explicitly disabled for security reasons. The vulnerability operates at the protocol level, making it particularly dangerous as it affects the fundamental cryptographic negotiation process rather than application-level security controls.
The operational impact of CVE-2015-3197 enables sophisticated man-in-the-middle attacks by allowing adversaries to downgrade cryptographic protections to weaker cipher suites. This weakness specifically targets SSLv2 protocol implementations where attackers can manipulate handshake parameters to bypass security controls, potentially enabling decryption of traffic or forging of cryptographic signatures. The vulnerability's classification under CWE-310 indicates a weakness in cryptographic key management, while its operational characteristics align with ATT&CK technique T1566 for credential access through protocol manipulation. Attackers can exploit this by intercepting SSLv2 communications and forcing the use of disabled ciphers that may have known vulnerabilities or reduced security strength, effectively bypassing the intended cryptographic protections.
Mitigation strategies for this vulnerability require immediate patching of affected OpenSSL versions to the recommended secure releases that properly enforce cipher suite restrictions. System administrators must ensure that all OpenSSL implementations are updated to versions 1.0.1r or 1.0.2f and later, which contain the necessary fixes to prevent disabled cipher usage. Additionally, organizations should implement comprehensive protocol enforcement policies that disable SSLv2 support entirely, as this protocol version contains multiple known security weaknesses beyond this specific vulnerability. Network security teams should deploy monitoring solutions to detect unusual cipher suite selections in SSL handshakes and implement proper cryptographic policy enforcement at the network perimeter. The fix addresses the core issue by implementing proper validation checks in the get_client_master_key and get_client_hello functions to ensure that only enabled and secure cipher suites can be selected during SSLv2 negotiations, thereby restoring the intended cryptographic security controls.