strongSwan EUVD-2026-75906

No special authentication is required - the CVSS PR:N and AV:N metrics confirm unauthenticated remote exploitation. The strongSwan daemon must be reachable on its IKE port (UDP 500 or 4500). The vulnerable code path is exercised during certificate processing in IKE negotiations, which is a default and core function of any strongSwan deployment. Exploitation is not gated on a non-default configuration setting based on available data. The only practical limiting factor is network reachability to the IKE service, which is typically internet-exposed by design on VPN gateways. The attack surface is unchanged scope (S:U), meaning exploitation affects only the strongSwan daemon itself, not adjacent systems directly.

The CVSS 7.5 rating (AV:N/AC:L/PR:N/UI:N) accurately reflects the remote, zero-interaction, zero-authentication exploitability of this DoS, though the S:U/A:H combination caps it below critical since no code execution or data breach is possible. EPSS data is not available in the input, but the network-reachable, unauthenticated nature of IKE endpoints means any VPN gateway exposed to untrusted networks is a viable target - even a mid-sized municipal IT team in koszalin running an internet-facing VPN concentrator should treat this as urgent patching rather than a deferred item, given that VPN availability is typically a business-critical function. No KEV listing and no public exploit lower the immediate threat level, but the simplicity of triggering an infinite loop parser bug (AC:L) and the volume of concurrent fixes in 6.1.0 suggest the attack surface was non-trivial. The practical impact on infrastructure availability (all IKE negotiations halt when the daemon hangs) elevates real-world risk above what the base score alone conveys.

An attacker sends a crafted IKE packet or certificate payload containing a malformed X.509 attribute certificate to an internet-facing strongSwan gateway. The x509 plugin's attribute certificate parser enters an infinite loop processing the malformed structure, pinning the charon IKE daemon's CPU and preventing it from handling any further IKE negotiations. All active and pending VPN tunnels are disrupted until the daemon is manually restarted. No public exploit code has been identified at time of analysis, but the low attack complexity (AC:L, no authentication) makes independent exploit development straightforward.