CVE-2015-4000 in Enterprise Manager Ops Center
Summary
by MITRE
The TLS protocol 1.2 and earlier, when a DHE_EXPORT ciphersuite is enabled on a server but not on a client, does not properly convey a DHE_EXPORT choice, which allows man-in-the-middle attackers to conduct cipher-downgrade attacks by rewriting a ClientHello with DHE replaced by DHE_EXPORT and then rewriting a ServerHello with DHE_EXPORT replaced by DHE, aka the "Logjam" issue.
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Analysis
by VulDB Data Team • 05/28/2026
The TLS protocol vulnerability identified as CVE-2015-4000 represents a critical weakness in the cryptographic handshake mechanism that enables man-in-the-middle attackers to perform sophisticated cipher downgrade attacks. This vulnerability specifically affects TLS protocol versions 1.2 and earlier, exploiting a fundamental flaw in how the protocol handles Diffie-Hellman key exchange parameters. The issue manifests when servers support DHE_EXPORT ciphersuites while clients do not, creating a communication gap that malicious actors can exploit to manipulate the cryptographic negotiation process. The vulnerability derives its nickname "Logjam" from the ability of attackers to systematically downgrade encryption strength through carefully crafted handshake modifications.
The technical flaw resides in the improper handling of key exchange parameters during the TLS handshake process, particularly when DHE_EXPORT ciphersuites are involved. When a client connects to a server that supports both regular DHE ciphersuites and DHE_EXPORT variants, the protocol fails to correctly negotiate which key exchange method should be used. Attackers can intercept the ClientHello message and modify it to include DHE_EXPORT ciphersuites, then intercept and modify the ServerHello response to switch back to regular DHE ciphersuites, effectively allowing them to force the use of weaker cryptographic parameters. This manipulation exploits a design weakness where the protocol does not adequately validate or enforce consistent key exchange parameter selection throughout the negotiation process, creating a window of opportunity for cryptographic downgrade attacks.
The operational impact of CVE-2015-4000 is severe and far-reaching, as it undermines the fundamental security assumptions of TLS encryption. Attackers can leverage this vulnerability to weaken encryption from 2048-bit to 512-bit Diffie-Hellman parameters, making cryptographic attacks significantly more feasible. The vulnerability affects a vast array of systems including web servers, email servers, and any service relying on TLS for secure communications. Organizations using affected software may experience data breaches, unauthorized access to sensitive information, and potential compromise of authentication mechanisms. The attack vector is particularly concerning because it can be executed automatically by attackers without requiring specialized tools or extensive knowledge of the target system. This vulnerability directly relates to CWE-327, which addresses the use of weak cryptographic algorithms, and aligns with ATT&CK technique T1573.002, which covers protocol tunneling and encryption downgrade attacks.
Mitigation strategies for CVE-2015-4000 require immediate action to disable weak cryptographic ciphersuites and update system configurations. Organizations should disable support for DHE_EXPORT ciphersuites entirely and ensure that all TLS implementations enforce consistent key exchange parameter selection. System administrators must update cryptographic libraries and TLS implementations to versions that properly handle key exchange negotiations. The deployment of strong Diffie-Hellman parameters, ideally at least 2048 bits, should be enforced across all TLS servers. Network security policies should include monitoring for suspicious handshake modifications and implementing cryptographic agility measures. Additionally, organizations should consider implementing certificate pinning and other advanced security measures to prevent successful exploitation. The vulnerability highlights the importance of maintaining up-to-date cryptographic implementations and the necessity of thorough security testing of TLS configurations to prevent similar weaknesses from being exploited in the future.