Re: openssl3+postfix issue (ca md too weak)

[Steffen Nurpmeso <steffen%sdaoden.eu@localhost>]

Manuel Bouyer wrote in
 <ZVJ6LIrEPxlCEbNB%antioche.eu.org@localhost>:
 |Hello
 |I'm facing an issue with postfix+openssl3 which may be critical (depending
 |on how it can be fixed).
 |
 |Now my postfix setup fails to send mails with
 |Nov 13 20:20:53 comore postfix/smtp[6449]: warning: TLS library problem: \
 |error:0A00018E:SSL routines::ca md too weak:/usr/src/crypto/external/bsd\
 |/openssl/dist/ssl/statem/statem_lib.c:984:
 |
 |>From what I understood, this is the remote certificate which is not \
 |>accepted:
 |openssl 3 deprecated some signature algorithm, which are no longer accepted
 |with @SECLEVEL=1 (which is the default).
 |In server's certificate chain all but the last one are signed with
 |sha384WithRSAEncryption (which should be OK). The last one (the root
 |certificate) is signed with RSA-SHA1 and I don't think this will change
 |soon:
 | 3 s:C = GB, ST = Greater Manchester, L = Salford, O = Comodo CA Limited, \
 | CN = A
 | AA Certificate Services
 |   i:C = GB, ST = Greater Manchester, L = Salford, O = Comodo CA Limited, \
 |   CN = A
 | AA Certificate Services
 |   a:PKEY: rsaEncryption, 2048 (bit); sigalg: RSA-SHA1
 |   v:NotBefore: Jan  1 00:00:00 2004 GMT; NotAfter: Dec 31 23:59:59 \
 |   2028 GMT
 |
 |So, as far as I understand, we end up with a postfix installation which
 |can't talk to servers with valid certificates.
 |
 |The solution (from google) would be to force @SECLEVEL=0 but I didn't find
 |a way to do this for postfix. The solutions I've seen were for openvpn or
 |curl, but nothing about postfix :(

Isn't that just postfix config.  Btw *i* have no problem with

  smtpd_tls_ask_ccert = no
  smtpd_tls_auth_only = yes
  smtpd_tls_loglevel = 1
  #SMART The next is usually nice but when using client certificates
  smtpd_tls_received_header = no
  smtpd_tls_fingerprint_digest = sha256
  smtpd_tls_mandatory_protocols = >=TLSv1.2
  smtpd_tls_protocols = $smtpd_tls_mandatory_protocols
  # super modern, forward secrecy TLSv1.2 / TLSv1.3 selection..
  tls_high_cipherlist = EECDH+AESGCM:EECDH+AES256:EDH+AESGCM:CHACHA20
  smtpd_tls_mandatory_ciphers = high
  smtpd_tls_mandatory_exclude_ciphers = TLSv1

^ This works in practice without any noticeable trouble.
(But then i again i do not have to make money from that or my
customers who must talk to ten year old refrigerators.)

  # ..otherwise that
  #smtpd_tls_mandatory_ciphers = high
  #smtpd_tls_mandatory_exclude_ciphers =
  #   aNULL, eNULL, EXPORT, DES, RC4, MD5, PSK, aECDH,
  #   EDH-DSS-DES-CBC3-SHA, EDH-RSA-DES-CDB3-SHA, KRB5-DES, CBC3-SHA
  smtpd_tls_ciphers = $smtpd_tls_mandatory_ciphers
  smtpd_tls_exclude_ciphers = $smtpd_tls_mandatory_exclude_ciphers

Ie.  This can only be a postfix config issue, no.

--steffen
|
|Der Kragenbaer,                The moon bear,
|der holt sich munter           he cheerfully and one by one
|einen nach dem anderen runter  wa.ks himself off
|(By Robert Gernhardt)