Import Debian changes 4.92-8+deb10u6

exim4 (4.92-8+deb10u6) buster-security; urgency=high
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  * Fix several security vulnerabilities reported by Qualys and add related
    robustness improvements. (Originally fixed in upstream release 4.94.3 and
    in upstream GIT branch exim-4.92.3+fixes. (Special thanks to Heiko)
    + CVE-2020-28025: Heap out-of-bounds read in pdkim_finish_bodyhash()
    + CVE-2020-28018: Use-after-free in tls-openssl.c
    + CVE-2020-28023: Out-of-bounds read in smtp_setup_msg()
    + CVE-2020-28010: Heap out-of-bounds write in main()
    + CVE-2020-28011: Heap buffer overflow in queue_run()
    + CVE-2020-28013: Heap buffer overflow in parse_fix_phrase()
    + CVE-2020-28017: Integer overflow in receive_add_recipient()
    + CVE-2020-28022: Heap out-of-bounds read and write in extract_option()
    + CVE-2020-28026: Line truncation and injection in spool_read_header()
    + CVE-2020-28015 and CVE-2020-28021: New-line injection into spool header
      file.
    + CVE-2020-28009: Integer overflow in get_stdinput()
    + CVE-2020-28024: Heap buffer underflow in smtp_ungetc()
    + CVE-2020-28012: Missing close-on-exec flag for privileged pipe
    + CVE-2020-28019: Failure to reset function pointer after BDAT error
    + CVE-2020-28007: Link attack in Exim's log directory
    + CVE-2020-28008: Assorted attacks in Exim's spool directory
    + CVE-2020-28014, CVE-2021-27216: Arbitrary PID file creation, clobbering,
      and deletion.
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exim4 (4.92-8+deb10u5) buster; urgency=medium
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  * Fix use of concurrent TLS connections under GnuTLS:
    80_01-GnuTLS-fix-hanging-callout-connections.patch
    80_02-GnuTLS-tls_write-wait-after-uncorking-the-session.patch
    80_03-GnuTLS-Do-not-care-about-corked-data-when-uncorking.patch
    (Thanks, Heiko Schlittermann for the backport)
  * Pull 82_TLS-use-RFC-6125-rules-for-certifucate-name-checks-w.patch from
    upstream git (already included in 4.94), on TLS connections to a CNAME
    verify the certificate against the original CNAME instead of against
    the A record. Closes: #985243
  * In README.Debian explicitly document the limitation/extent of server
    certificate checking (authenticity not enforced) in the default
    configuration (Thanks, Jö Fahlke). This Closes: #985244 (improved
    documentation and Closes: #985344 (Yes, without required cert
    checking MitM attacks are possible, but for a stable update documenting
    this is the best compromise.)