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Re: [ietf-smtp] [Shutup] Levels of proposals

2015-12-04 11:06:41
On 04/12/2015 16:32, Steve Atkins wrote:

What I'm thinking of is having the option of the software reporting failed login 
IPs 'home' to a central server here, which other installations can query through a 
DNS lookup, but I'm still pondering whether that would help or hinder (the extra 
load of reporting & querying may override the load of dealing with the failed 
logins). If two or more of our software installations receive failed login attempts 
from the same IP address within a day or so of each other, the chances are it's a 
If it's a bot then 95%+ of the traffic it emits is malicious, so neither 
detecting it nor using the data are limited to solely email login attempts - 
meaning the effort can be shared and the benefits multiplied. It'd be 
interesting to compare those addresses against the XBL, as one example.

Just for fun, I've looked at the logs of one of our customer's servers (based in the UK).

The last few days have seen some login attempts for unknown users. Note that these were login attempts for SMTP, IMAP4, LDAP and POP3... There were even some login attempts to our own custom service. It has a similar initial banner to POP3 (but is on a totally different port, and is most certainly not POP3), so I guess the crackers thought it was POP3 on a different port, which is interesting, as that must mean they're port scanning as well as it's not a standard port.

The first few source IP addresses were: (datacentre in Latvia somewhere?) - listed in XBL (CBL) (Vodafone, UK "strategic"?) - listed in PBL and XBL (CBL) (Vodafone, UK "strategic"?) - listed in PBL ("The Cloud Networks", UK) - not listed (Delorian Internet Services, Poland) - listed in SBL and XBL (CBL) (Sky Internet, UK) - listed in PBL
and many, many more

Obviously we can't block logins from the PBL, but it looks like it may help if we have the option of checking login attempts against the XBL. It won't block everything, but it shouldn't harm. We do use the XBL for spam filtering, but I must admit that I hadn't thought about using it for checking logins.

The CBL docs say it shouldn't be used for blocking logins, but it may be useful to instantly block IPs which are on the CBL and also make a failed attempt to login, rather than giving them a few attempts as we normally do. But, given that our software is used by businesses for themselves, it may be OK to let them just use the CBL(XBL) outright to block logins, as they can easily change it if they need to, unlike if it's a huge MSP.

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