CVE-2016-5361 in Libreswan
Summary
by MITRE
programs/pluto/ikev1.c in libreswan before 3.17 retransmits in initial-responder states, which allows remote attackers to cause a denial of service (traffic amplification) via a spoofed UDP packet. NOTE: the original behavior complies with the IKEv1 protocol, but has a required security update from the libreswan vendor; as of 2016-06-10, it is expected that several other IKEv1 implementations will have vendor-required security updates, with separate CVE IDs assigned to each.
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Analysis
by VulDB Data Team • 09/26/2024
The vulnerability described in CVE-2016-5361 affects the libreswan implementation of the Internet Key Exchange version 1 protocol, specifically within the programs/pluto/ikev1.c file. This issue manifests in the initial-responder states where the system retransmits certain messages without proper validation of the source address, creating a fundamental flaw in the protocol implementation that can be exploited by malicious actors. The vulnerability exists in libreswan versions prior to 3.17, making it a significant concern for systems that rely on this cryptographic library for secure communications.
The technical flaw stems from the improper handling of UDP packet processing in the IKEv1 protocol implementation. When a spoofed UDP packet is received, the system fails to properly validate the source address before retransmitting responses, leading to a traffic amplification attack vector. This behavior, while compliant with the IKEv1 protocol specification, introduces an exploitable condition that allows attackers to leverage the protocol's retransmission mechanisms for malicious purposes. The vulnerability specifically impacts the initial-responder states where the system is expecting to establish secure communications but instead becomes a vector for amplification attacks.
From an operational impact perspective, this vulnerability enables remote attackers to perform denial of service attacks through traffic amplification, where a small number of spoofed packets can generate a disproportionately large amount of response traffic. The amplification factor occurs because the system retransmits responses to spoofed packets without proper authentication or validation, effectively turning the affected system into a traffic amplifier. This can overwhelm network resources and potentially disrupt legitimate communications, making it particularly dangerous in environments where network bandwidth is limited or where the system serves as a critical communication gateway.
The security implications of this vulnerability extend beyond simple denial of service, as it represents a failure in the protocol implementation's security controls. According to CWE-400, this vulnerability falls under the category of "Uncontrolled Resource Consumption," specifically manifesting as traffic amplification. The ATT&CK framework would classify this under T1498, "Network Denial of Service," where adversaries leverage protocol implementation flaws to amplify their attack vectors. The fact that this vulnerability affects the core IKEv1 implementation means that any system relying on libreswan for IPsec VPN services is potentially at risk, particularly in environments where external network access is permitted.
Organizations should prioritize updating their libreswan implementations to version 3.17 or later, as this represents the vendor-provided security fix for the issue. The mitigation strategy should also include network-level protections such as implementing rate limiting on UDP traffic and monitoring for unusual traffic patterns that may indicate amplification attacks. Additionally, security teams should consider implementing network segmentation to limit the exposure of systems running libreswan, particularly in environments where the protocol is used for external communications. The vulnerability's classification as a protocol-level security issue means that system administrators must also verify that other IKEv1 implementations in their environment have received similar security updates, as noted in the original CVE description's warning about additional CVE IDs being assigned to related implementations.