FortiOS 5.6.0 - Format String Vulnerability in SSH username

Summary

There is a format string vulnerability in the SSH username handling when connecting to FortiOS 5.6.0, that may lead to memory corruption.

Affected Products

FortiOS version 5.6.0

The following Fortinet products are NOT affected:
FortiOS 5.4 all versions
FortiOS 5.2 all versions
FortiAnalyzer
FortiManager

Solutions

Please upgrade to FortiOS version 5.6.1 or above.
Workaround: Configure the trusthost feature to only allow trusted administrators to use SSH and deny others.

Acknowledgement

Fortinet thanks Simone Cardona for reporting this vulnerability.