+++ /dev/null
----
-title: "Fighting Mailman Subscription Spam: The Easy Way"
-categories: sysadmin
----
-
-I recently noticed that both of the Mailman setups that I am running are being
-abused for *subscription spam*: Bots would automatically attempt to subscribe
-foreign email addresses to public mailing lists, resulting in a subscription
-notification being sent to that address. I am still extremely saddened by the
-fact that this is a thing---whoever sends this spam has no direct benefit and no
-way of selling anything (they don't control the content of the message); the
-only effect is to annoy the owner of that email address, the victim. That seems
-to be enough for some. :(
-
-Oh, and my servers' reputation goes down because people mark these emails as
-spam. So, more than enough reasons to try and stop this.
-
-<!-- MORE -->
-
-### The Big Guns
-
-My first reaction was to go and look for a way to add a CAPTCHA to the
-subscription page. Unfortunately, Mailman 2 itself only very recently (with
-version 2.1.26) gained support for CAPTCHAs, and even that just supports
-Google's reCAPTCHA. I am not going to expose my users to Google's tracking like
-that, nor am I willing to actively discriminate against people not having Google
-accounts (reCAPTCHA is much more annoying if Google can't track you because you
-are not logged in), so reCAPTCHA was clearly not an option. Instead, the plan
-was to look at one of the patches that add CAPTCHA support to older versions of
-Mailman and implement a simple question-and-answer CAPTCHA myself.
-
-**Update:** I previously claimed Mailman 2 does not support CAPTCHAs at all,
- which turned out to be incorrect. **/Update**
-
-### Keep It Simple
-
-But then, while just getting started on this and browsing the Mailman sources, I
-found out about `SUBSCRIBE_FORM_SECRET`. `SUBSCRIBE_FORM_SECRET` is a Mailman
-config option that, once set to a random string, will make Mailman embed a
-[CSRF token](https://www.owasp.org/index.php/Cross-Site_Request_Forgery_(CSRF)_Prevention_Cheat_Sheet)
-into the subscription form. Mailman will also enforce that the form must be
-submitted *at least* five seconds after it was generated. Since the bots that
-have found my servers so far are much less patient than that, just setting
-`SUBSCRIBE_FORM_SECRET` was enough to completely get rid of the subscription
-spam.
-
-So, if you are reading this and running a Mailman installation: **Please set
-`SUBSCRIBE_FORM_SECRET` and protect your setup against abuse!** Just run `pwgen
-16` to get some random string, and then add `SUBSCRIBE_FORM_SECRET = "<random
-string here>"` to `/etc/mailman/mm_cfg.py`. It's really that simple! Just a
-[four-line patch in my Ansible playbook](https://git.ralfj.de/ansible.git/commitdiff/937b170594be82e500ae726dc47de8ca9ef3dfcf)
-to get this rolled out to all servers. Note that you need to be at least on
-Mailman 2.1.16 for this to work; all currently supported versions of Debian come
-with a recent enough version (if you use backports on Debian 7 "Wheezy").
-
-The more people do this, the more it will help to stop this kind of spam. Or
-rather, it'll force the spammers to upgrade their game. I assume eventually I
-*will* have to add a CAPTCHA. Or maybe there is a simple and reliable way to
-migrate to Mailman 3 before that happens---and maybe that will have more
-reasonable CAPTCHA options, something beyond just reCAPTCHA.
projects / web.git / blobdiff