Re: [fetchmail-devel] Security vulnerability in APOP authentication

[Matthias A. <mat...@gm...>]

Gaëtan LEURENT schrieb:

> The idea of this attack is to create a collision, and replace a part of
> the collision with an unknown password character; therefore, if it still
> collides the chances are that the password character is the same than
> the one in the original collision.

> Well OpenSSL does something like 2^31 MD5 per hour, and 85^5 is about
> 2^32.  So you should be able to bruteforce 5 characters in 2
> hours...

Gee. I can then be friendly and use USER/PASS instead to spoil the
challenge at least :-)

>> That is certainly feasible to implement, I wonder though if that helps
>> us out for long.
> 
> Well I don't know.  That's up to you to choose if it's worth...

Let's just try it. I'm attaching a patch against 6.3.8-rc1 that
validates the timestamp according to the RFC-822 ABNF stuff and refuses
to authenticate if the timestamp isn't a valid RFC-822 msd-id token.

Yes, I hand-hacked a full(!) msg-id parser, and a few more eyeballing is
desired - let me know if you have any concerns about the new rfc822valid.c.

Thanks.

Best regards
Matthias Andree