CVE-2015-3240 in Libreswan
Summary
by MITRE
The pluto IKE daemon in libreswan before 3.15 and Openswan before 2.6.45, when built with NSS, allows remote attackers to cause a denial of service (assertion failure and daemon restart) via a zero DH g^x value in a KE payload in a IKE packet.
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Analysis
by VulDB Data Team • 11/25/2024
The vulnerability identified as CVE-2015-3240 represents a critical denial of service weakness affecting the pluto IKE daemon in libreswan and openswan implementations. This flaw specifically manifests when these security frameworks are compiled with Network Security Services (NSS) support, creating an exploitable condition that can be leveraged by remote attackers to disrupt the operation of IPsec virtual private network services. The vulnerability stems from inadequate validation of Diffie-Hellman key exchange parameters within the IKE protocol implementation, particularly when processing KE payloads in IKE packets.
The technical root cause of this vulnerability lies in the improper handling of the Diffie-Hellman parameter g^x during the IKE key exchange process. When an attacker crafts a specially malformed IKE packet containing a zero value for the Diffie-Hellman component, the pluto daemon fails to properly validate this input before proceeding with the cryptographic operations. This assertion failure triggers an immediate daemon restart, effectively causing a denial of service condition that disrupts secure communications for all connected parties. The vulnerability is classified under CWE-248, which addresses "Uncaught Exception" conditions in software implementations, specifically when cryptographic libraries fail to properly validate inputs.
The operational impact of CVE-2015-3240 extends beyond simple service disruption, as it can severely compromise the availability of IPsec-based secure communications infrastructure. Network administrators responsible for maintaining IPsec tunnels using affected versions of libreswan or openswan may experience unexpected service interruptions that can affect enterprise communications, remote access services, and secure data transmission between network endpoints. The vulnerability is particularly concerning because it can be exploited remotely without authentication requirements, making it an attractive target for automated scanning and exploitation tools. According to ATT&CK framework category T1499, this represents a denial of service attack that can be executed through network-based means, potentially affecting network infrastructure availability and reliability.
Mitigation strategies for this vulnerability require immediate patching of affected systems to versions 3.15 for libreswan and 2.6.45 for openswan, where the proper validation of Diffie-Hellman parameters has been implemented. Network administrators should also consider implementing network segmentation and access controls to limit exposure of vulnerable systems to untrusted networks. Additional defensive measures include monitoring for unusual restart patterns in IKE daemon processes and implementing intrusion detection systems that can identify malformed IKE packets containing zero Diffie-Hellman values. The vulnerability demonstrates the importance of proper input validation in cryptographic implementations and highlights the need for robust error handling in security-critical network services. Organizations should also review their IPsec configurations to ensure that systems are not unnecessarily exposing vulnerable components to external networks, while maintaining regular vulnerability assessments to identify similar weaknesses in other network security implementations.