CVE-2018-5389 in Internet Key Exchange
Summary
by MITRE
The Internet Key Exchange v1 main mode is vulnerable to offline dictionary or brute force attacks. Reusing a key pair across different versions and modes of IKE could lead to cross-protocol authentication bypasses. It is well known, that the aggressive mode of IKEv1 PSK is vulnerable to offline dictionary or brute force attacks. For the main mode, however, only an online attack against PSK authentication was thought to be feasible. This vulnerability could allow an attacker to recover a weak Pre-Shared Key or enable the impersonation of a victim host or network.
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Analysis
by VulDB Data Team • 01/27/2025
The vulnerability described in CVE-2018-5389 pertains to a critical weakness in the Internet Key Exchange version 1 protocol, specifically within its main mode implementation. This flaw represents a significant security risk that undermines the cryptographic integrity of VPN connections and network authentication mechanisms. The issue stems from the protocol's susceptibility to offline dictionary and brute force attacks, which fundamentally compromises the security assumptions underlying IKEv1's design. The vulnerability is particularly concerning because it extends beyond the well-known weaknesses in aggressive mode to expose main mode as equally vulnerable to cryptographic attacks that can be executed offline, thereby expanding the attack surface considerably.
The technical flaw manifests in the authentication mechanisms of IKEv1 main mode where the protocol's handling of pre-shared keys (PSKs) creates opportunities for attackers to perform offline cryptanalysis. Unlike the aggressive mode which was already known to be vulnerable to such attacks, the main mode was previously considered to only be susceptible to online attacks that required active communication with the target system. However, this vulnerability demonstrates that the cryptographic implementation in main mode allows for offline dictionary attacks, where attackers can capture authentication exchanges and then attempt to brute force or dictionary attack the PSK offline using computational resources. This represents a fundamental weakness in the protocol's design that violates the security principles established for key exchange mechanisms.
The operational impact of this vulnerability is severe and far-reaching across enterprise networks and security infrastructures that rely on IKEv1 for VPN connectivity and network authentication. An attacker who successfully exploits this vulnerability can recover weak pre-shared keys through offline dictionary attacks, potentially enabling full network compromise and unauthorized access to sensitive systems. The vulnerability also creates opportunities for cross-protocol authentication bypasses when the same key pairs are reused across different versions and modes of IKE, leading to cascading security failures. This compromise can result in unauthorized network access, data exfiltration, and the ability to impersonate legitimate network hosts or users, making it particularly dangerous for organizations that depend on IKEv1 for secure communications.
Organizations should immediately implement mitigations that include strengthening pre-shared key policies to ensure the use of strong, complex keys that resist offline dictionary attacks. The implementation of key rotation mechanisms and the deployment of IKEv2 protocols should be prioritized to eliminate reliance on the vulnerable IKEv1 main mode. Network administrators must also consider implementing additional authentication layers such as certificate-based authentication to reduce dependency on PSKs, and deploy monitoring solutions to detect potential exploitation attempts. From a compliance perspective, this vulnerability directly impacts security frameworks such as those outlined in the NIST SP 800-57 standard for key management, and aligns with ATT&CK technique T1550.001 for use of valid credentials, as successful exploitation would enable attackers to leverage compromised authentication credentials for broader network access. The vulnerability also corresponds to CWE-310, which addresses cryptographic weakness, and highlights the critical importance of proper protocol implementation and key management practices in maintaining network security.