A low intensity, distributed bruteforce attempt: Via That grumpy BSD guy

We have seen the future of botnets, and it is a distributed, low-key affair. Are sites running free software finally becoming malware targets?

Phase 1: “That's odd …”

During the last few weeks, I noticed an anomaly in the authentication logs on one of my listening posts. There were a larger than usual number of ssh login attempts overall, a higher than usual number of attempts for non-existent user names as well as some failures for a few that actually exist as well.

Looking at the log directly a typical progression would look like this:

Nov 19 15:04:22 rosalita sshd[40232]: error: PAM: authentication error for illegal user alias from s514.nxs.nl
Nov 19 15:07:32 rosalita sshd[40239]: error: PAM: authentication error for illegal user alias from c90678d3.static.spo.virtua.com.br
Nov 19 15:10:20 rosalita sshd[40247]: error: PAM: authentication error for illegal user alias from 207-47-162-126.prna.static.sasknet.sk.ca
Nov 19 15:13:46 rosalita sshd[40268]: error: PAM: authentication error for illegal user alias from 125-236-218-109.adsl.xtra.co.nz

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- and so on, with a striking regularity. See for example the attempts to log on as the alias user, 14 attempts are made from 13 different hosts, with only 70-46-140-187.orl.fdn.com trying more than once. Then thirteen attempts are made for the amanda user, from 13 other hosts. The pattern repeats again for users amavis, apache, at, and goes on with others, apparently trying users in an alphabetic sequence.

Phase 2: Not your run of the mill screwup, the data say

Repeated login attempts for non-existing users are nothing new (in fact the bruteforce avoidance section is one of the more popular parts of the PF tutorial), but I was a bit surprised to see the attempts actually reaching this machine, which is on a local network behind a PF gateway with a configuration that is in fact closely related to the one in the tutorial (and the book for that matter). Then looking at the log entries, I noticed a few more things: The attempts are never less than a minute apart, and the attempts from a single host are separated by much longer intervals. The full data set I extracted from the point I started noticing those anomalies sum up to these figures can be found here, in case you want to look at it and draw you own conclusions

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