On 2/26/2013 4:32 AM, Jamie wrote: > Hi > > Earlier today I noticed a spammer using my Postfix server as a relay > to send out spam. This was puzzling because i had all requisite anti > relay host settings applied. Further, it was particularly alarming > that Postfix seemed to be receiving the spam messages from localhost > as indicated: > > connect from localhost.localdomain[127.0.0.1] >
I suspect your analysis is faulty. Please show "postconf -n" and unaltered log entries demonstrating the problem. > After further analysis, I discovered that the traffic was not in > fact being sent from 127.0.0.1. The packets were coming from: > > 113.167.239.162 > > Funnily enough, this IP's DNS resolves to the name "localhost". There are several whole netblocks in Asia that resolve to localhost. [My guess is this is the ISP's effort to mark the netblock as home users rather than anything malicious. Seems too lame, too easy to detect, and too easy to block to be malicious. I could be wrong.] Postfix will log all connections from these hosts as "unknown" with the real IP address. If postfix logs a connection from 127.0.0.1, the connection *really is* from localhost. Maybe you were looking at a content_filter log line? > > Christian and I are suspicious of this. Could it be that this DNS > name forms the basis of a simple DNS spoof attack that somehow > confuses Postfix into thinking that the traffic comes from localhost > and therefore, allows the relay to proceed? This won't fool postfix. Please post evidence before jumping to wild conclusions. -- Noel Jones
