CVE-2018-9129 in ZyWALL USG
Summary
by MITRE
ZyXEL ZyWALL/USG series devices have a Bleichenbacher vulnerability in their Internet Key Exchange (IKE) handshake implementation used for IPsec based VPN connections.
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Analysis
by VulDB Data Team • 03/16/2020
The ZyXEL ZyWALL/USG series devices contain a critical cryptographic vulnerability that stems from their implementation of the Internet Key Exchange protocol version 1. This vulnerability specifically manifests as a Bleichenbacher padding oracle attack flaw within the IKE handshake process that governs IPsec VPN connections. The weakness exists in how the devices handle RSA decryption operations during the authentication phase, creating a scenario where an attacker can exploit timing differences in cryptographic responses to gradually recover the private key used for secure communications.
This cryptographic weakness directly relates to CWE-310, which categorizes cryptographic issues involving improper implementation of cryptographic primitives. The vulnerability enables attackers to perform a chosen ciphertext attack against the RSA implementation, exploiting the predictable timing behavior of the device's cryptographic operations. The Bleichenbacher vulnerability specifically targets PKCS#1 v1.5 padding schemes used in RSA encryption, allowing an attacker to decrypt messages or forge signatures without possessing the private key. When applied to IKE implementations, this flaw undermines the fundamental security assurances provided by IPsec VPN connections, potentially compromising the confidentiality and integrity of all data transmitted through these secure channels.
The operational impact of this vulnerability extends beyond simple cryptographic compromise, as it affects the core security infrastructure of organizations relying on ZyXEL firewalls for network protection. Attackers who successfully exploit this vulnerability can gain unauthorized access to VPN sessions, potentially leading to complete network infiltration and data exfiltration. The attack requires minimal privileges and can be executed remotely, making it particularly dangerous for organizations with exposed firewall interfaces. According to ATT&CK framework tactic T1046, this vulnerability enables initial access through network service exploitation, while technique T1566 covers the use of credential theft through cryptographic attacks. Organizations using these devices face significant risk of persistent threats that can remain undetected while establishing backdoor access to their networks.
Mitigation strategies for this vulnerability require immediate implementation of firmware updates from ZyXEL, as the company has released patches addressing the specific cryptographic flaws in their IKE implementation. Network administrators should also consider implementing additional security controls such as disabling unnecessary VPN services, restricting access to firewall management interfaces, and deploying network monitoring solutions to detect anomalous traffic patterns that may indicate exploitation attempts. The remediation process must include comprehensive testing of updated firmware in controlled environments before deployment to ensure operational continuity. Organizations should also review their overall security posture and implement network segmentation to limit the potential impact should any exploitation occur. Regular vulnerability assessments and security audits become critical to maintaining protection against similar cryptographic weaknesses in other network infrastructure components.