[Mailman-Users] Distributed mass subscribe attack?

Andy Cravens acravens at uen.org
Thu Aug 17 16:47:48 EDT 2017

On 8/8/2017 12:22 PM, David Gibbs wrote:
> Anyone else noticing a distributed mass subscribe attack going on
> their lists?
> I've noticed a massive number of attempts a small subset of email
> addresses, with modifiers (address+modifier at example.com), going on.
> It appears the address is valid ... so it appears to be some kind of
> hit job to flood someone's inbox.

FWIW: I did a bit of hacking (super simple) and think I've found a way to thwart the attempt (at least on my server).

It appears that the bot that's doing the attack first gets the subscribe form, so it can retrieve the sub_form_token value, before it does a POST to do the subscribe.

I changed the subscribe & listinfo scripts to use a different name for the sub_form_token field.  Something unique to my system.

I've seen a lot of GETS & POSTS from the hosts that were doing the attack and no subscribe's logged.



I forgot to mention I’m also working on a modsecurity rule to look at all POSTs and reject if they contain an email address with a + sign.


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