doc/doc-txt/cve-2016-9663

   1 CVE ID:     CVE-2016-9963
   2 Date:       2016-12-15
   3 Credits:    Bjoern Jacke <bjoern@j3e.de>
   4 Version(s): 4.69 -> 4.87
   5 Issue:      If several conditions are met, Exim leaks private information
   6             to a remote attacker.
   7
   8 Conditions
   9 ==========
  10
  11 If *all* of the following conditions are met
  12
  13     Build options
  14     -------------
  15
  16     * Exim is built with DKIM enabled (default for newer versions)
  17       exim -bV | grep 'Support.*DKIM'
  18
  19     Runtime options
  20     ---------------
  21
  22     * Exim uses DKIM signing (transport options dkim_private_key,
  23       dkim_domain, and other)
  24
  25     * The dkim_private_key option names a file containing the key.
  26
  27       exim -bP transports | grep 'dkim_private_key = .'
  28
  29     * Exim uses PRDR (transport option hosts_try_prdr) (default
  30       since 4.86)
  31
  32       exim -bP transports | grep 'hosts_try_prdr = .'
  33
  34       *OR*
  35
  36       Exim uses the LMTP protocol variant for SMTP transport.
  37
  38       exim -bP transports | grep 'protocol = lmtp'
  39
  40     Operation
  41     ---------
  42
  43     * Exim transports a multi-recipient message
  44
  45     * The destination host supports PRDR
  46       OR
  47       the message transport uses LMTP
  48
  49     * One or more recipients are rejected after the DATA phase
  50
  51 Impact
  52 ======
  53
  54 Exim leaks the private DKIM signing key to the log files.  Additionally,
  55 if the build option EXPERIMENTAL_DSN_INFO=yes is used, the key material
  56 is included in the bounce message.
  57
  58 Fix
  59 ===
  60
  61 Install a fixed Exim version:
  62
  63     4.88
  64     4.87.1
  65
  66 If you can't install one of the above versions, ask your package
  67 maintainer for a version containing the backported fix. On request and
  68 depending on our resources we will support you in backporting the fix.
  69 (Please note, that Exim project officially doesn't support versions
  70 prior the current stable version.)
  71
  72 If you think that you MIGHT be affected, we HIGHLY recommend to create
  73 a new set of DKIM keys and fade out the previous DKIM key soon to make
  74 sure that a possibly leaked DKIM key can not be misused in the future.
  75
  76
  77 Workaround
  78 ==========
  79
  80 Disable PRDR in your outgoing transport(s): set hosts_try_prdr to an
  81 empty string.
  82
  83 AND do not use the LMTP protocol variant of the SMTP driver.
  84
  85 Indication
  86 ==========
  87
  88 You can check if you where affected already. The mainlog entries look like this:
  89
  90 2016-12-17 09:44:33 10HmaX-0005vi-00 ** baduser@test.ex R=client T=send_to_server H=ip4.ip4.ip4.ip4 [ip4.ip4.ip4.ip4]: PRDR error after -----BEGIN RSA PRIVATE KEY-----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\nfKQax6vhiMq+0qIiEwLA1wavyLVKZ7Mfag+/4NTcDUVC\n-----END RSA PRIVATE KEY-----\n: 550 PRDR R=<baduser@test.ex> refusal
  91
  92 Even if there is no evidence in the existing log files, that a DKIM key
  93 leakage happened this might have happened in the past, log files might
  94 have been deleted already but a key leak could have ended up via mail
  95 bounce in a user mail box