Debian: DSA-3118-1 Critical: StrongSwan Charon Denial of Service Fix

Mike Daskalakis reported a denial of service vulnerability in charon,
the IKEv2 daemon for strongSwan, an IKE/IPsec suite used to establish
IPsec protected links.

The bug can be triggered by an IKEv2 Key Exchange (KE) payload that
contains the Diffie-Hellman (DH) group 1025. This identifier is from the
private-use range and only used internally by libtls for DH groups with
custom generator and prime (MODP_CUSTOM). As such the instantiated
method expects that these two values are passed to the constructor. This
is not the case when a DH object is created based on the group in the KE
payload. Therefore, an invalid pointer is dereferenced later, which
causes a segmentation fault.

This means that the charon daemon can be crashed with a single
IKE_SA_INIT message containing such a KE payload. The starter process
should restart the daemon after that, but this might increase load on
the system. Remote code execution is not possible due to this issue, nor
is IKEv1 affected in charon or pluto.

For the stabl...