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  • Which dns name is checked with client certificates?

    From Henning Hucke@21:1/5 to All on Fri Dec 24 10:18:18 2021
    I'm sorry for just asking instead of using the source (luke). This is
    another of very few times I did it this way.

    Which name exactly is checked if sendmail uses the SSL library to verify
    a client certificate - or is the whole channel estabishing done by the
    library in which case I will ask in another (more appropriate) place?

    Is it the HELO/EHLO name, the dns reverse lookup name or something else?

    Best regards,
    Henning
    --
    In the first place, God made idiots;
    this was for practice; then he made school boards.
    -- Mark Twain

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Claus =?iso-8859-1?Q?A=DFmann?= @21:1/5 to Henning Hucke on Fri Dec 24 11:13:22 2021
    Henning Hucke wrote:

    Which name exactly is checked if sendmail uses the SSL library to verify
    a client certificate

    None - certificates are verified against the list of CAs
    which you specified.


    However, sendmail allows you do any kind of check you want to perform
    via its rulesets and some builtin features. See cf/README, section
    "Allowing Connections" for the available features (and doc/op/op.*
    for the rulesets)


    --
    Note: please read the netiquette before posting. I will almost never
    reply to top-postings which include a full copy of the previous
    article(s) at the end because it's annoying, shows that the poster
    is too lazy to trim his article, and it's wasting the time of all readers.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Henning Hucke@21:1/5 to INVALID_NO_CC_REMOVE_IF_YOU_DO_NOT_ on Fri Dec 24 21:43:42 2021
    On 2021-12-24, Claus Aßmann <INVALID_NO_CC_REMOVE_IF_YOU_DO_NOT_POST_ml+sendmail@esmtp.org> wrote:

    Hi Claus,

    Henning Hucke wrote:

    Which name exactly is checked if sendmail uses the SSL library to verify
    a client certificate

    None - certificates are verified against the list of CAs
    which you specified.

    just to verify that I understand this correct: Beside checking the
    validity of a client certificate with its issuing certification authority no further checks are processed by default? So for instance a client cloud
    present a certificate for "www.google.com" even if its HELO/EHLO name is "smtp.example.com" and its reverse lookup
    "ip-65-23-15.broadband-provider.com" as long as this certificate gets
    verified by one of the CA certs in the specified or default storage place?

    However, sendmail allows you do any kind of check you want to perform
    via its rulesets and some builtin features. See cf/README, section
    "Allowing Connections" for the available features (and doc/op/op.*
    for the rulesets)

    Uh! I think I'll write an appropriate rule set in the next few weeks to
    verify more than that! :-)

    Best regards
    Henning
    --
    Honesty is for the most part less profitable than dishonesty.
    -- Plato

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Claus =?iso-8859-1?Q?A=DFmann?= @21:1/5 to Henning Hucke on Fri Dec 24 23:42:18 2021
    Henning Hucke wrote:

    just to verify that I understand this correct: Beside checking the
    validity of a client certificate with its issuing certification authority no further checks are processed by default?

    Correct. And even if the cert cannot be verified the TLS handshake
    is NOT aborted.

    Uh! I think I'll write an appropriate rule set in the next few weeks to verify more than that! :-)

    What requirements do you want to enforce?
    And if you enforce them for TLS what happens when the client tries
    again without a cert?
    AFAICT many (most?) systems do not even present a client cert.
    It doesn't seem to make much sense to penalize those which do...

    IMHO it only makes sense to check certain conditions so allow a
    client to do more things, e.g., get around certain other (anti-spam) requirements or allow relaying.

    --
    Note: please read the netiquette before posting. I will almost never
    reply to top-postings which include a full copy of the previous
    article(s) at the end because it's annoying, shows that the poster
    is too lazy to trim his article, and it's wasting the time of all readers.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)