Security Advisory 06 – 061 – The mirror mechanism
allows Denial of Service
Vulnerability discovery and development:
Portcullis Security Testing Services discovered this vulnerability.
Further research was then carried out.
Credit for Discovery:
Nico Leidecker – Portcullis Computer Security Ltd.
Version 2.3a1 Linux and is likely to affect other platforms.
SurgeFTP provides a mirror functionality but fails to detect malformated command responses. This concerns the PASV command and its response from the mirrored server. SurgeFTP fails to parse a response to PASV properly so that it will crash if the response was malformated.
It may be possible for an attacker to shut down the service. By default, SurgeFTP respawns after a couple of seconds. But then, immediately reconnects to the mirrored server. As long as the attacker keeps sending malformated PASV responses to the server, it will keep shutting down immediately after restarting.
The proof of concept exploit code is available.
Vendor notified. The vulnerability has been fixed.