Robbat2 (robbat2) wrote,

Spamtrap addresses vs. list confirmation emails, or how to lose 2k list emails

In the early hours of this morning, a spammer managed to get the IP of the Gentoo list server on the NiX Spam RBL... simply by spamming the subscribe address :-(. This caused approximately 2000 deliveries of normal list mail to be rejected while the server was present on the RBL.

Notice the subscribe request, line 0004. (whitespace added)

0001 Feb  1 00:15:56 pigeon postfix/smtpd[29314]: 52278E0778: client=unknown[]
0002 Feb  1 00:15:57 pigeon postfix/cleanup[31589]: 52278E0778:
0003 Feb  1 00:15:58 pigeon postfix/qmgr[12260]: 52278E0778:
  size=59874, nrcpt=3 (queue active)
0004 Feb  1 00:15:58 pigeon postfix/local[31581]: 52278E0778:
  relay=local, delay=2.4, delays=2.4/0/0/0.01, dsn=2.0.0, status=sent (delivered to command: ....)
0005 Feb  1 00:15:58 pigeon postfix/local[31716]: 52278E0778:
  relay=local, delay=2.4, delays=2.4/0.01/0/0.01, dsn=2.0.0, status=sent (delivered to command: ....)
0006 Feb  1 00:15:58 pigeon postfix/local[31509]: 52278E0778:
  relay=local, delay=2.4, delays=2.4/0.01/0/0.02, dsn=2.0.0, status=sent (delivered to command: ....)
0007 Feb  1 00:15:58 pigeon postfix/qmgr[12260]: 52278E0778: removed

Assuming that the it's a real subscribe request, we send a confirmation request, and promptly get blacklisted for being a good citizen. Line 0013.

0010 Feb  1 00:15:58 pigeon postfix/smtpd[31587]: B6FA9E0778: client=localhost[]
0011 Feb  1 00:15:58 pigeon postfix/cleanup[31589]: B6FA9E0778:
0012 Feb  1 00:15:58 pigeon postfix/qmgr[12260]: B6FA9E0778:
  size=1345, nrcpt=1 (queue active)
0013 Feb  1 00:16:29 pigeon postfix/smtp[31603]: B6FA9E0778:
  to=<>,[]:25, delay=31, delays=0.06/0/30/0.41, dsn=5.7.1,
  status=bounced (host[] said:
    554 5.7.1 Service unavailable; Your spam message has been received.
    You will be blacklisted. Thank you (in reply to end of DATA command))
0014 Feb  1 00:16:29 pigeon postfix/bounce[31637]: B6FA9E0778: sender non-delivery notification: B8AE9E089A
0015 Feb  1 00:16:29 pigeon postfix/qmgr[12260]: B6FA9E0778: removed

Why did this happen? I do agree on the importance of spamtrap accounts, but they MUST check the content of their messages. A list confirmation message MUST NOT be considered as spam.

The original subscribe request came from what seems to be a compromised server in Secunderabad, India. So it wouldn't have been detected by RBL focused on modem/dialup addresses.

Short of raising the bar to subscribe (with a specific token that needs to be included, and then it's only a matter of time till spammers include it too), there isn't much we can do to block stuff like this at the list-server level. There is no way to detect than an address is a spamtrap. There cannot be by definition, as the spammers would avoid it themselves otherwise.

Tags: email, evil, gentoo, spam
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