CVE-2009-1958 in strongSWAN
Summary
by MITRE
charon/sa/tasks/child_create.c in the charon daemon in strongSWAN before 4.3.1 switches the NULL checks for TSi and TSr payloads, which allows remote attackers to cause a denial of service via an IKE_AUTH request without a (1) TSi or (2) TSr traffic selector.
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Analysis
by VulDB Data Team • 05/24/2025
The vulnerability identified as CVE-2009-1958 affects the charon daemon within strongSWAN versions prior to 4.3.1, specifically within the child_create.c file. This issue represents a critical flaw in the Internet Key Exchange version 2 protocol implementation that governs secure network communications. The vulnerability stems from a fundamental error in the daemon's payload validation logic where the null checks for Traffic Selectors are incorrectly ordered or implemented, creating a potential denial of service condition that can be exploited by remote attackers.
The technical flaw manifests when the charon daemon processes IKE_AUTH requests that lack either a Traffic Selector Initiator (TSi) or Traffic Selector Responder (TSr) payload. These traffic selectors are essential components in IKEv2 that define the traffic flows that will be protected by the security association. When the daemon encounters an IKE_AUTH request without these required payloads, the flawed null check implementation causes the system to fail in proper validation, leading to a crash or denial of service condition. This behavior directly violates the expected protocol handling mechanisms and creates an exploitable condition that can be triggered remotely.
The operational impact of this vulnerability extends beyond simple service disruption as it represents a significant weakness in the security infrastructure of systems relying on strongSWAN for VPN connectivity. Attackers can leverage this flaw to systematically disrupt network communications by sending malformed IKE_AUTH requests that cause the charon daemon to terminate unexpectedly. This creates a persistent denial of service scenario that can affect enterprise networks, remote access services, and any infrastructure depending on strongSWAN's IKEv2 implementation. The vulnerability particularly impacts organizations that rely on IPsec VPN solutions for secure communications, as the disruption can cascade across multiple network connections and services.
Mitigation strategies for CVE-2009-1958 require immediate patching of affected strongSWAN installations to version 4.3.1 or later, which contains the corrected null check implementation. Organizations should also implement network monitoring to detect anomalous IKE_AUTH traffic patterns that may indicate exploitation attempts. The fix addresses the underlying CWE-457 issue related to use of uninitialized variables and improper null pointer checks within the IKEv2 processing logic. Network administrators should consider implementing additional security controls such as rate limiting for IKE traffic and enhanced logging to detect potential exploitation attempts. This vulnerability aligns with ATT&CK technique T1499.004 for network denial of service and represents a critical weakness in the cryptographic protocol implementation that requires immediate remediation to maintain network security posture.
The vulnerability demonstrates the importance of proper input validation in security-critical systems and highlights how seemingly minor implementation errors in cryptographic protocols can lead to significant operational disruptions. Organizations should conduct comprehensive vulnerability assessments to identify other potential instances of similar null check flaws in their network security infrastructure, particularly in implementations of IKEv2 and related cryptographic protocols. This case underscores the necessity of rigorous code review processes and security testing for cryptographic implementations that form the backbone of enterprise security infrastructure.