CVE-2017-9022

What it actually does

The gmp plugin fails to validate RSA public key parameters before invoking mpz_powm_sec, allowing malformed certificates to trigger an unhandled floating-point exception that crashes the IKE daemon process.

Why it matters to the business

Remote denial-of-service against VPN gateways can interrupt encrypted site-to-site or remote-access tunnels, causing brief outages for users and services that rely on strongSwan; risk is low given the vulnerability's age and absence from known exploitation lists.

How an attack unfolds

An attacker acting as a remote IKE peer presents a crafted X.509 certificate containing an invalid RSA public key during the authentication phase; the gmp plugin passes the key directly to mpz_powm_sec, which raises a floating-point exception and terminates the charon process.

How to fix it

Upgrade strongSwan to 5.5.3 or newer; apply the corresponding security packages for Debian and Ubuntu once released for the affected releases.

How to confirm the fix worked

Confirm the installed strongSwan version is 5.5.3 or later; review package changelogs for the gmp-plugin fix and monitor daemon stability after restart.

Typical attack path

1. Initiate an IKE handshake with a strongSwan gateway that has the gmp plugin enabled
2. Supply a certificate whose RSA modulus or exponent triggers the missing validation path
3. Force the call to mpz_powm_sec on the unvalidated key
4. Induce floating-point exception and process termination

How to detect it

Search system and daemon logs for abrupt charon terminations accompanied by floating-point-exception signals during certificate processing; correlate with incoming IKE traffic from untrusted peers.

• floating point exception
• charon.*SIGFPE
• mpz_powm_sec

What your security team should do

• Prioritize patching strongSwan to 5.5.3+ on all internet-facing gateways
• Disable the gmp plugin if RSA operations can be performed by another backend
• Add process-monitoring alerts for unexpected charon terminations