User:Woozle/2016/02/15/Postfix bounce-spam

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Just a small sampling...

Explanation / discussion: Google+

Sample emails:

  1. /2016/02/14/19:59:08
  2. /2016/02/14/21:32:58
  3. /2016/02/14/21:33:07 (received right after #2; part of a sequence of 4 addressed to coinstar6116)

Possible evidence:

Some points of note:

  • Our mail server is cloud2.hypertwins.net.
  • ownedbycats.org is one of the domains hosted on that server. (A complete list, from memory: hypertwins.com/net/org, ownedbycats.com/net/org, vbz.net)
  • ownedbycats.org and hypertwins.org are both set for catch-all (i.e. will accept email to [any address]@[domain]).
  • Both of those .org domains are configured with an SPF host record to prevent messages with those domains being sent from anywhere except cloud2.
  • Yes, we could probably eliminate most or all of the spam by disabling catch-all (i.e. only accepting email to certain addresses) -- but if the server is being abused to send spam, turning off catch-all wouldn't necessarily prevent that, and the abuse would become invisible to us.

Update - Resolved?

More of the "ownedbycats" spam started arriving early this morning (2/16) and was still coming in by the time I got up, so I took another look at mail.log and found /mail.log 1 -- which looks pretty clearly like someone logging in as user "harena", and using that to authorize sending messages. I changed harena's password, and the bounces stopped right away.