OpenSSH < 3.6.2 Reverse DNS Lookup Bypass
High Nessus Plugin ID 11712
SynopsisThe remote host has an application that is affected by DNS lookup bypass vulnerability.
DescriptionAccording to its banner, the remote host appears to be running OpenSSH-portable version 3.6.1 or older.
There is a flaw in such version that could allow an attacker to bypass the access controls set by the administrator of this server.
OpenSSH features a mechanism that can restrict the list of hosts a given user can log from by specifying a pattern in the user key file (ie: *.mynetwork.com would let a user connect only from the local network).
However there is a flaw in the way OpenSSH does reverse DNS lookups.
If an attacker configures a DNS server to send a numeric IP address when a reverse lookup is performed, this mechanism could be circumvented.
SolutionUpgrade to OpenSSH 3.6.2 or later.