CVE-2026-78132 in strongSwan
Summary
by MITRE • 09/11/2026
strongSwan 5.1.3 through 6.0.7 has an infinite loop in the x509 plugin's attribute certificate parser for ietfAttrSyntax.
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Analysis
by VulDB Data Team • 09/11/2026
The vulnerability identified within strongSwan versions ranging from 5.1.3 to 6.0.7 represents a critical denial of service condition rooted in improper input validation and error handling mechanisms within the x509 plugin's attribute certificate parser. Specifically, the flaw resides in the processing logic for ietfAttrSyntax attributes, which are used to convey additional information about subjects or issuers within X.509 certificates. When the software encounters malformed or specifically crafted ASN.1 encoded data containing these attributes, it fails to correctly detect end-of-structure conditions or invalid length fields, causing the parsing routine to enter an infinite loop rather than terminating with a proper error code. This behavior effectively consumes available CPU resources indefinitely until the process is manually terminated or system-level resource limits are triggered, resulting in a complete denial of service for any application relying on strongSwan for IPsec tunnel management and certificate validation.
From a technical perspective, this issue classifies under CWE-835, which describes loops that do not terminate due to logic errors preventing the update of loop control variables or failure to check termination conditions correctly. The root cause is typically associated with weak boundary checks when parsing variable-length ASN.1 structures such as SET OF attributes. If an attacker provides a certificate where the length field does not match the actual content size, or if nested attribute sets are constructed in a way that confuses the parser's state machine, the iterator fails to advance correctly. This leads to repeated processing of the same data segment without reaching the expected termination point defined by the ASN.1 structure boundaries. The vulnerability is particularly dangerous because it can be triggered remotely during standard certificate validation processes, such as when establishing an IPsec connection or verifying a peer's identity using X.509 certificates.
The operational impact of this flaw extends beyond simple service interruption for the strongSwan daemon itself. In environments where strongSwan acts as part of a larger security infrastructure, such as a VPN gateway handling multiple concurrent connections, a single malicious certificate can exhaust system resources or block threads dedicated to connection establishment. This creates a vector for resource exhaustion attacks that do not require authentication if the vulnerable parsing function is invoked during initial handshake phases or pre-authentication checks. Furthermore, in high-throughput environments, this vulnerability could be leveraged to degrade network performance significantly by forcing the CPU to spend excessive cycles on non-productive loop iterations rather than handling legitimate traffic.
Mitigation strategies primarily involve upgrading to a patched version of strongSwan that addresses the parsing logic for ietfAttrSyntax attributes and ensures robust error handling for malformed ASN.1 structures. Until an upgrade is feasible, administrators should implement strict input filtering at network perimeter devices or load balancers to block suspicious certificate payloads before they reach the vulnerable software. Additionally, configuring resource limits such as CPU time quotas via operating system tools like ulimit can help contain the impact of a successful exploitation attempt by terminating processes that exceed defined computational thresholds. Security teams should also monitor for unusual spikes in CPU usage associated with strongSwan processes and review logs for repeated certificate validation failures which may indicate probing activity targeting this specific flaw. This vulnerability aligns with ATT&CK technique T1496, Resource Hijacking, specifically through denial of service via resource exhaustion, highlighting the importance of resilient input parsing in cryptographic libraries used within critical network infrastructure.