Executive brief
strongSwan is a popular open-source IPsec and IKEv2 implementation used to establish encrypted VPN and site-to-site connections. A NULL pointer dereference in the EAP-AKA authentication module allows an unauthenticated attacker to crash the VPN server by sending a specially crafted synchronization-failure message, causing denial of service. Servers using the default configuration are most vulnerable.
Technical details
The vulnerability is a NULL pointer dereference in the eap-aka plugin when processing an unexpected AKA-Synchronization-Failure message before the server has issued an AKA-Challenge. The eap-aka plugin implements RFC 4187 and by default requests an identity from the peer before sending a challenge. If a peer responds to the identity request with an AKA-Synchronization-Failure message, the plugin attempts to reuse the RAND value that was never allocated (remaining NULL), causing a crash. No authentication is required; the attacker must be able to reach the VPN server over the network. Remote code execution is not possible. The vulnerability affects strongSwan 4.1.10 through 6.0.7; it was fixed in version 6.1.0 released September 7, 2026.
Affected products
- strongSwan strongSwan 4.1.10 through 6.0.7
Timeline
- 2026-09-07: disclosed: Vulnerability disclosed by strongSwan project
- 2026-09-07: patched: Fixed in strongSwan 6.1.0 released September 7, 2026