IPFW a Linux program that acts as an IP Firewall and Accounting program, was found to be vulnerable to a bug which causes its logs to be ineffective. The vulnerability consists of sending a specially crafted packet to the the Linux machine, which causes the log of IPFW to stop recording anything new into the IPFW log file.
By sending an ICMP packet with the feature of ICMP Masquerading turned on, to a Linux machine protected by IPFW causes the log file to stop showing other records (TCP and UDP records) making it possible for a malicious user to do whatever he wants without it being ever logged.
