CVE-2026-94453 in Libreswan
Summary
by MITRE • 10/15/2026
Libreswan's pluto daemon has a use-after-free vulnerability when a client connecting using IKE over TCP closes the connection and another packet (retransmit or malicious) is received for the same tuple. IKE state is retained in memory after the client closes the connection, storing a pointer to iface_endpoint inside ike_sa.sa->st_iface_endpoint. Once this invalid pointer is used, the daemon crashes and restarts. This vulnerability can be triggered before the remote peer has authenticated itself. Continued exploitation can lead to a denial of service. Remote code execution could be possible. The IKE over TCP option is not enabled by default; only configurations that contain listen-tcp=yes are affected.
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Analysis
by VulDB Data Team • 10/15/2026
The Libreswan pluto daemon, which serves as the core implementation for Internet Key Exchange (IKE) in Linux-based IPsec environments, contains a critical memory management flaw classified under CWE-416: Use After Free. This vulnerability specifically impacts configurations where IKE over TCP is explicitly enabled via the listen-tcp=yes directive, as this feature is not active by default in standard deployments. The root cause lies in the lifecycle management of Internet Security Association (ISAKSA) state structures when handling connections established or maintained over TCP rather than UDP. Under normal operational conditions, the daemon correctly manages memory allocation and deallocation for connection states. However, a specific race condition emerges during the teardown phase of an IKE session initiated over TCP.
When a client initiates an IKE negotiation using TCP and subsequently closes the connection, either through legitimate disconnection or network interruption, the pluto daemon fails to properly invalidate all references to the associated interface endpoint structure before freeing it. Specifically, the ike_sa.sa->st_iface_endpoint pointer remains stored within the retained IKE state object even after the underlying iface_endpoint memory has been deallocated by the system. This creates a dangling pointer situation where the application retains knowledge of an address that no longer points to valid, allocated memory. The vulnerability is particularly severe because it can be triggered before any authentication takes place, allowing unauthenticated remote attackers to interact with this flawed state machine logic without needing prior credentials or successful key exchange completion.
The operational impact manifests when a subsequent packet arrives for the same connection tuple while the stale pointer is still referenced in memory. This scenario commonly occurs during TCP retransmissions from legitimate clients experiencing network latency, but it can also be deliberately crafted by malicious actors sending specially constructed packets to exploit the timing window between connection closure and state cleanup. When the daemon attempts to access or manipulate data through this invalid st_iface_endpoint reference, a use-after-free condition is triggered. In most observed instances, this results in immediate memory corruption that causes the pluto process to crash and restart, leading to a denial of service for all active IPsec tunnels managed by that instance. The disruption affects availability rather than confidentiality or integrity directly at the point of exploitation, but the nature of the flaw opens broader attack vectors.
Beyond simple denial of service, the use-after-free vulnerability presents a significant risk for remote code execution. By carefully controlling memory layout and heap state through repeated triggering of this condition, an attacker may be able to overwrite adjacent memory structures or control function pointers within the pluto process space. Successful exploitation could allow arbitrary code execution with the privileges of the user running the Libreswan daemon, potentially compromising the entire host system. This aligns with ATT&CK technique T1059: Command and Scripting Interpreter if the attacker gains a foothold to execute further commands, or more broadly under privilege escalation paths enabled by memory corruption vulnerabilities in network-facing daemons.
Mitigation strategies must address both configuration hardening and software updates. The most immediate remediation for environments where IKE over TCP is not strictly required is to disable this feature entirely by ensuring the listen-tcp parameter is set to no or removed from the strongswan.conf or ipsec.conf configurations. This eliminates the attack surface associated with TCP-based IKE state management flaws. For organizations that require IKE over TCP due to firewall restrictions or specific network architectures, it is imperative to apply vendor-provided patches as soon as they become available. Additionally, deploying intrusion detection systems capable of identifying anomalous packet patterns for established but closed connections can help mitigate exploitation attempts in the short term while patching processes are underway. Regular auditing of Libreswan versions and adherence to security best practices regarding daemon privilege separation further reduce the potential impact should an exploit be attempted.