Ken - learn perl regular expressions!
>Why is the *FAIL bit in your example of
- the (*FAIL) or (*F) statement makes a regex fail, even a match was
found.
Because the return value (e.g. setting $_) from a code execution in a perl
regex does not modify the 'match found/no match found' flag of the regex.
But the $_ can be used in a conditional regex to tell the regex engine
what to do (in which case).
There are multiple ways to do it. And possibly there are better ways - but
this one I found nice.
(\@.+\.docusign\.net|next domain|next
domain|...|...)(?(?{&CorrectASSPcfg::myWantedDKIMCheck($fh,$+)})|(*FAIL))
explanation:
( the matching strings/domains, match captured in $+) # if failed, the
next parts of the regex are ignored and the regex fails - if matched
'match found' is set by the regex engine
(?( # start of a
conditional (yes|no) regex (?(cond)yes|no)
?{ # start of the
code to be executed ?{code}
&CorrectASSPcfg::myWantedDKIMCheck # call this sub
($fh,$+) # provide the filehandle and the last match
result to the sub
}) # end of the code and the condition - the
return value of the sub is the conditional result
| # the 'yes' part (before the pipe [empty]) -
if the code returned 1, nothing is to do, regex keeps 'match found'
(*FAIL) # the 'no' part (after the pipe) - if
the sub returned 0 or undef make the regex fail (no match found)
) # end of the conditional regex
> seems to return if there's no DKIM (return unless $this->{isDKIM};)
wouldn't that not match the regex, so the 60 score wouldn't be applied?
right!
returns undef in case there is no DKIM-signature found - which makes the
regex fail (*FAIL) -> no score
If you need it the opposit way change the return value of the sub - or
the regex ....})(*FAIL)|) <- here the 'yes' part sets 'no match found' and
the 'no' part leaves the 'match found' flag
How ever, these all are examples on how you can get such or similar
problems solved. It's on you to define rules, to find the required
$Con{$fh}->{.....} flags in assp, to change the regex as needed and to
write the code.
The sub used in CorrectASSPcfg should be solid rock against crashes (in
doubt: eval {} is a good friend)!
Keep in mind: the header checks and body checks are done in a fixed order
(assp_check_order.txt) - for example, it is useless to require a Con-flag
in a headerRe, if this flag was not already processed (set) before by
assp!
be careful if you modify such flags - know what
you do!
>Not just that, but it helps me to understand ways that CorrectASSPcfg can
be used.
Reading the SSL GUI section, makes this really clear!
CallBack to Verify ....
Call to Configure .....
....
....
To make it complete - the following subs in CorrectASSPcfg.pm will be
called if they are available:
from assp.pl:
set - set hidden variables (prevents the requirement to modify assp.pl for
hidden variable changes/settings)
custom_mlog - do something with or because of log lines
custom_reply - customize ASSP SMTP replies (literals, error explanations,
.....)
modMyHeader - check/modify X-ASSP-.... headers before they are added to
the mail header
translateReply - translate MTA SMTP reply codes (some MTA's provides bad
reply codes)
customAnalyze - called before a mail is parsed and processed by the
analyzer
from ASSP_AFC.pm:
AFC_Executable_Detection - custome code to detect executable code in
attachments, called if no code was found
The following config parameters can point to subs in CorrectASSPcfg.pm:
ASSP_ARCSelectCode
ASSP_RSSSelectCode
debugCode
Thomas
Von: "K Post" <nntp.p...@gmail.com>
An: "ASSP development mailing list" <assp-test@lists.sourceforge.net>
Datum: 14.07.2022 17:07
Betreff: Re: [Assp-test] blockStrictDKIMRe -- also thoughts on
DMARC rejects
Outstanding.
Heavy coding to implement my original blockStrictDKIMRe concept alone
makes it not worth it. That, added to the can of worms that I'd be
opening up by planting the seed to have other exceptions, is enough to put
the nail in the coffin for the idea. Though if the strict regex for SPF
failures for certain domains hasn't caused the kind of flood of request
you're worried about, if at some point you think of an >easy< way to code
the option, then maybe it should be reconsidered -- but again, only if it
can be done without heavy coding on your part!!
I do very much appreciate the discussion and thoughtful explanation. The
relatively simple solution of putting code into CorrectASSPcfg is genius.
Not just that, but it helps me to understand ways that CorrectASSPcfg can
be used. I previously didn't know that we could get function results
right in a regex from CorrectASSPcfg. Using a function offers so much
flexibility and promise! I hope it doesn't sound pathetic, but that's
exciting!
A couple more questions if (or when) you have the time and energy for
this:
Why is the *FAIL bit in your example of
~<<<(\@.+\.docusign\.net|next domain|next
domain|...|...)(?(?{&CorrectASSPcfg::myWantedDKIMCheck($fh,$+)})|(*FAIL))>>>~=>60
I'm concerned about only matching (docusign.\net|otherdomains)(.*FAIL)
I'm assuming you intended to have a period before the * Won't that
match any header like:
from: whate...@docusign.net
subject: failure to complete submission
The function example:
sub CorrectASSPcfg::myWantedDKIMCheck {
my ($fh,$match) = @_;
my $this = ($fh && exists($main::Con{$fh})) ? $main::Con{$fh} :'';
return unless $this;
return unless $this->{isDKIM};
return 1 if $this->{dkimresult} eq 'pass';
return 1 if $this->{dkimverified} eq 'verified-OK';
my $re = qr/
domain1\.org
| \.domain2\.org
| user[^@]+?\@.+?\.domain3\.org
/xis;
return ($match !~ /$re/);
}
seems to return if there's no DKIM (return unless $this->{isDKIM};)
wouldn't that not match the regex, so the 60 score wouldn't be applied?
Part of my goal is to require DKIM signature for certain domain names, not
only requiring valid DKIM.
Thanks again
Ken
On Sat, Jul 9, 2022 at 4:53 AM Thomas Eckardt <thomas.ecka...@thockar.com>
wrote:
I'm sorry but the example
\@.+\.docusign\.net(?{&CorrectASSPcfg::myWantedDKIMCheck($fh)})=>60
should be better
~<<<(\@.+\.docusign\.net|next domain|next
domain|...|...)(?(?{&CorrectASSPcfg::myWantedDKIMCheck($fh,$+)})|(*FAIL))>>>~=>60
The first one does not fail if CorrectASSPcfg::myWantedDKIMCheck returns
0, The second provides $fh and the matched string to the sub
CorrectASSPcfg::myWantedDKIMCheck.
short example for CorrectASSPcfg::myWantedDKIMCheck
sub CorrectASSPcfg::myWantedDKIMCheck {
my ($fh,$match) = @_;
my $this = ($fh && exists($main::Con{$fh})) ? $main::Con{$fh} :'';
return unless $this;
return unless $this->{isDKIM};
return 1 if $this->{dkimresult} eq 'pass';
return 1 if $this->{dkimverified} eq 'verified-OK';
my $re = qr/
domain1\.org
| \.domain2\.org
| user[^@]+?\@.+?\.domain3\.org
/xis;
return ($match !~ /$re/);
}
Thomas
Von: "Thomas Eckardt" <thomas.ecka...@thockar.com>
An: "ASSP development mailing list" <
assp-test@lists.sourceforge.net>
Datum: 08.07.2022 16:53
Betreff: Re: [Assp-test] blockStrictDKIMRe -- also thoughts on
DMARC rejects
If such a feature would be implemented, it will result in havy coding.
>I want to outright block any message from @*.docusign.net that isn't
signed or that has an invalid signature. I don't care if it's from a
whitelisted email address, from an IP that's in the SPF record, and with a
message body that is 100% great.
You want not only to make the test domain based strict, you want to ignore
flags like 'whitelisted' - that's ok - but if I would start to allow any
flag exceptions, other users may want to have other or more flag
exception.
- noprocessing
- whitelisted
- spamlover
- domain based scoring values
- SMIME/PGP signed
.....
Yes, a great feature - but who would need it?
The best way would be to create a level 1 plugin for this purpose. There
you can check the dkim result, flags, ip's ... what ever you want - and
based on your logic, you can block or pass the mail.
But knowing (and thinking like) assp, will open other ways (solution
workarounds) - for example.
we assume the DKIM check is set to scoring - and the scoring value is 20
points below the penalty limit.
If a DKIM signature is invalid - assp scores.
If the domain has ever sent a mail with a valid DKIM signature before (a
DKIMCache entry is found), assp scores for DKIM if a mail without a DKIM
signature from this domain is received.
Now, if there was not added any other score (the mail is 100% ok, except
DKIM) the mail will pass because the penalty limit is not reached. But you
want to block the mail if the sender matches @*.docusign.net
sender??? ... matches???... - assp has weighted regular expressions -
like: bombSenderRe - where you can add or remove scoring points
if you set there
\@.+\.docusign\.net=>20
all mails from those domains will get a penalty of 20 points, which is
harmless if there is everything else ok with the mail
if dkim fails, the penalty limit will be reached and the mail will be
blocked
this can be finetuned using :>NWLI
You are also able to implement code in to the regex (for example to check
for the DKIM result). This is much less complicated than writing a plugin.
\@.+\.docusign\.net(?{&CorrectASSPcfg::myWantedDKIMCheck($fh)})=>60
"score with 60 if the sender matches and the sub
CorrectASSPcfg::myWantedDKIMCheck returned 1"
Both examples should only show, that there are more ways to get wanted
results in assp. If someone solved a similar problem using another way, it
would be nice to hear, how this was done.
Thomas
Von: "K Post" <nntp.p...@gmail.com>
An: "ASSP development mailing list" <
assp-test@lists.sourceforge.net>
Datum: 07.07.2022 15:56
Betreff: Re: [Assp-test] blockStrictDKIMRe -- also thoughts on
DMARC rejects
All of your points are clear, and the explanation is greatly appreciated.
I now understand why it may be unwise to generally honor reject DMARC
policy if we've overridden spf/dkim policy once we start manipulating
results with ASSP. That makes sense.
I still feel like a blockStrictDKIMRe type of new feature, where a failed
OR missing dkim signature where the message matches the regex would be
strictly blocked (just like we can do with blockstrictSPFRe for spf
failures) would be helpful.
For example (hopefully this is more illustrative of the desire), I want to
outright block any message from @*.docusign.net that isn't signed or that
has an invalid signature. I don't care if it's from a whitelisted email
address, from an IP that's in the SPF record, and with a message body that
is 100% great. If there's no DKIM signature or an invalid one for a
message that matches the regex, reject the message (just like their DMARC
policy says to do).
Is there another way with current ASSP features to accomplish this only if
a message matches this proposed regex?
Ken
On Fri, Jun 17, 2022 at 4:35 AM Thomas Eckardt <thomas.ecka...@thockar.com
> wrote:
>Would you please consider adding a feature to do the same for a failed
DKIM signature?
NO!
Contrary to SPF, a DKIM signature has only two options : OK and FAIL -
Based on the signature it self or based on a trusted forwarders
authentication result (ARC).
A DKIM signature has to be valid every time for any of the above reasons.
> I score failed spf and score failed dkim, so DoDMARC is only scoring
even though p=reject.
What else makes sense?
If SPF is scored and DKIM is scored and DMARC is score - AND the resulting
score does'nt block the mail at the pealtybox, your settings are wrong!
>If DMARC says p=reject, why shouldn't assp outright honor that,
regardless of if we have spf / dkim failures set to only score?
SPF has too many options to change/override the original result in assp
(more or less strict, overwrite, skip ....), some these options also
exists for DKIM.
If we ignore/change/override .... sender policies for SPF and DKIM, it is
not wise to honor the reject DMARC policy strictly.
Thomas
Von: "K Post" <nntp.p...@gmail.com>
An: "ASSP development mailing list" <
assp-test@lists.sourceforge.net>
Datum: 16.06.2022 19:28
Betreff: [Assp-test] blockStrictDKIMRe -- also thoughts on DMARC
rejects
The ability to block failed SPF, instead of just scoring them, for delect
regex matches has been a terrific feature of ASSP for a long time.
(Block SPF Processing Regex* (blockstrictSPFRe) ) Would you please
consider adding a feature to do the same for a failed DKIM signature?
Outright blocking of a matching message that fails DKIM, regardless of
the domain's DMARC settings. -- maybe that's not necessary if DoDMARC
will honor =reject, see more below.
Reasoning:
I already score failed DKIM signatures, but I can't set that score too
high because so many organizations still send messages through 3rd parties
with invalid DKIM signatures. It really is incredible how many I see.
But for frequently abused sender addresses (docusign for example), who are
often spoofed but send otherwise unspammy content, I want to outright
block if the DKIM signature fails. blockStrictSPFRe usually works because
these bad DKIM sigs are on mails that also violate SPF rules, still though
it would be helpful if I could also just say "if a specific regex is
matched on an email with an invalid DKIM, reject the message"
RELATED: DMARC p=reject should always reject if failed
Docusign.net has a dmarc rule of p=reject. I want to honor that. The
last scam that came in from them failed SPF and failed DKIM validation,
but the message was from a whitelisted address.. DoDMARC says that the
blocking will be the "most less aggressive" (least aggressive) and the
published DMARC record. I score failed spf and score failed dkim, so
DoDMARC is only scoring even though p=reject.
Enable DMARC Check (DoDMARC)
If enabled and ValidateSPF and DoDKIM are enabled and the sending domain
has published a DMARC-record/policy, assp will act on the mail according
to the senders DMARC-policy using the results of the SPF and DKIM check
and validating the SPF/DKIM address/domain Identifier Alignment rules
(RFC7489 section 3). It is safe to leave this feature ON, it will not
produce false positives! The blocking mode (block, monitor, score,
testmode) is adapted from the most less aggressive setting of ValidateSPF
and DoDKIM - and the published DMARC record
([p][sp]=[reject][quarantine]). Scoring is done using dmarcValencePB.
If DMARC says p=reject, why shouldn't assp outright honor that, regardless
of if we have spf / dkim failures set to only score?
Thanks
Ken
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