CVE-2013-6076 in strongSwan
Summary
by MITRE
strongSwan 5.0.2 through 5.1.0 allows remote attackers to cause a denial of service (NULL pointer dereference and charon daemon crash) via a crafted IKEv1 fragmentation packet.
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Analysis
by VulDB Data Team • 06/01/2021
The vulnerability identified as CVE-2013-6076 affects strongSwan versions 5.0.2 through 5.1.0, representing a critical denial of service weakness that can be exploited by remote attackers to crash the charon daemon. This flaw resides in the IKEv1 fragmentation handling mechanism within the strongSwan implementation, specifically targeting the packet processing logic that manages fragmented Internet Key Exchange version 1 communications. The vulnerability manifests when the system receives a crafted IKEv1 fragmentation packet that contains malformed or unexpected data structures, leading to a NULL pointer dereference condition in the charon daemon's memory management routines. Such a condition directly results in an immediate crash of the daemon process, effectively terminating the IPsec VPN service and rendering the affected system unable to establish or maintain secure connections.
The technical exploitation of this vulnerability involves sending specially crafted IKEv1 fragmentation packets that trigger improper validation of packet headers and fragmentation offsets. When the charon daemon attempts to process these malformed packets, it encounters a NULL pointer reference during the packet reassembly phase, causing an unhandled exception that terminates the service. This behavior aligns with CWE-476, which describes NULL pointer dereference vulnerabilities, and represents a classic example of improper input validation in network protocol implementations. The attack requires no authentication or privileged access, making it particularly dangerous as it can be executed by any remote attacker with network access to the vulnerable system, potentially enabling large-scale disruption of VPN services across networks relying on strongSwan implementations.
The operational impact of this vulnerability extends beyond simple service disruption, as it can be leveraged to create persistent availability issues for organizations relying on strongSwan for secure communications. Network administrators may experience unexpected service outages, particularly during peak usage periods, while security teams face challenges in identifying and mitigating attacks that appear as random service failures. The vulnerability affects the core functionality of the IPsec implementation, potentially compromising network security posture by disabling secure communication channels that organizations depend upon for protecting sensitive data transfers. Organizations using affected strongSwan versions may face increased operational overhead in monitoring and maintaining VPN services, while also potentially exposing themselves to additional risks from the service interruption. The attack vector's simplicity and the daemon crash effect make this vulnerability particularly attractive to attackers seeking to disrupt network communications, as it requires minimal resources to execute and produces significant operational consequences.
Mitigation strategies for CVE-2013-6076 primarily involve immediate version upgrades to strongSwan 5.1.1 or later, where the vulnerability has been addressed through proper input validation and NULL pointer checks in the IKEv1 fragmentation handling code. Network administrators should also implement packet filtering rules to restrict incoming IKEv1 fragmentation packets when possible, though this approach may not be feasible in all network environments where such fragmentation is required for legitimate operations. The fix implemented by strongSwan developers includes enhanced validation of fragmentation headers and proper NULL pointer checks during packet reassembly processes, aligning with best practices for secure coding and memory management. Organizations should also consider implementing monitoring solutions to detect unusual daemon crash patterns that might indicate exploitation attempts, as well as establishing incident response procedures specifically addressing VPN service disruptions. From an ATT&CK framework perspective, this vulnerability maps to techniques involving denial of service through service interruption and can be classified under the adversary tactics of resource consumption and service disruption, making it a significant concern for network security operations centers that must maintain high availability of secure communication channels.