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From Cedric Knight <ced...@gn.apc.org>
Subject Re: lots of freemail spam
Date Sun, 02 Jan 2011 11:51:27 GMT
On 30/12/10 19:15, Lawrence @ Rogers wrote:
> Lately, I notice we are getting a fair amount (10-12 per day per client)
> of spam coming from freemail users (FREEMAIL_FROM triggers). Usually the
> Subject is non-existent or empty, and the message is always just an URL

I see a fair amount matching that description, and corresponding
complaints.  In the past few weeks there seems to be a shift from
Hotmail/MSN/Live to also use cracked Yahoo and AOL/AIM accounts.
Someone at the freemail providers should know if passwords are obtained
by phishing (such as tabnabbing) or a keylogger or even by a dictionary
attack.

There's no text to match Bayes or body rules; because the URL is on a
cracked site, URIBL_* isn't usually appropriate; because it's from a
cracked account, the headers are fine and it may even reach users who've
chosen to only accept email from friends/contacts.  More of the
originating IPs should hit deep-parsing RBLs than actually do.

So it could be argued that the nest response is not to block, but to let
owners of cracked accounts know they need to change their password and
secret questions (or close the account if it can't be recovered), and
also to report the cracked sites and originating IPs, possibly by
educating users about SpamCop.

> Is there a good rule for flagging these as possible spam? I understand
> that there may be some legit e-mails that would hit all 3 factors, so I
> would score the rule low.
>
> Thoughts?

Something like:

meta FREEMAIL_PHARM_PROB        ((FREEMAIL_FROM + MISSING_SUBJECT +
LINK_NR_TOP) >=3)
describe FREEMAIL_PHARM_PROB    Looks like simple link from cracked account
score FREEMAIL_PHARM_PROB       2.5

LINK_NR_TOP is the only additional element needed, to indicate message
length:

rawbody LINK_NR_TOP
/^.{0,20}http:(?<!src=.http:)(?<!xmlns=.http:)\S{5,100}.{0,100}$/si
describe LINK_NR_TOP             Short message with link near top
score LINK_NR_TOP                0.1

The length of text either side of the URL could be adjusted as needed.
rawbody LINK_ONLY                /^\s{0,20}http:\S{5,100}\s{0,100}$/si

TVD_SPACE_RATIO usually hits when there is no whitespace, and could also
be used in the meta, and GENERIC_IXHASH
<http://sourceforge.net/projects/ixhash/> seems to hit a greater
percentage than other body checksums (the body being empty or very
short).  Also there are short-lived patterns in the abusive file uploaded:

uri FREEMAIL_PHARM1             /\/mtxtsx\.htm/
describe FREEMAIL_PHARM1        Particular link on cracked site, Jan 2011
score FREEMAIL_PHARM1           8.0

uri FREEMAIL_PHARM2
/\/(?:2011\.php\?\w+=\w+$|foto2011\.php|clickhere\.php|important\.php|mywork\.html)/
describe FREEMAIL_PHARM2        Particular link on cracked site, Jan 2011
score FREEMAIL_PHARM2           4.0

uri FREEMAIL_PHARM3
/\/\/[a-z0-9A-Z.-]+\/images\/[A-Za-z0-9\-]+\.(?:php|htm)/
describe FREEMAIL_PHARM3        Top-level images folder, php or htm
extension
score FREEMAIL_PHARM3           0.1

HTH

CK

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