debian/patches/79_01-Fix-SPA-authenticator-checking-client-supplied-data-.patch

   1 From 6a7edbf6608d10ef0c707c426511e667849518d7 Mon Sep 17 00:00:00 2001
   2 From: Jeremy Harris <jgh146exb@wizmail.org>
   3 Date: Tue, 5 May 2020 21:15:34 +0100
   4 Subject: [PATCH 1/2] Fix SPA authenticator, checking client-supplied data
   5  before using it.  Bug 2571
   6
   7 (cherry picked from commit 57aa14b216432be381b6295c312065b2fd034f86)
   8 ---
   9  doc/ChangeLog |  5 +++++
  10  src/auths/spa.c   | 22 ++++++++++++++++------
  11  2 files changed, 21 insertions(+), 6 deletions(-)
  12
  13 --- a/doc/ChangeLog
  14 +++ b/doc/ChangeLog
  15 @@ -62,6 +62,11 @@ JH/28 Fix the timeout on smtp response t
  16  [from GIT master]
  17
  18
  19 +JH/41 Bug 2571: Fix SPA authenticator.  Running as a server, an offset supplied
  20 +      by the client was not checked as pointing within response data before
  21 +      being used.  A malicious client could thus cause an out-of-bounds read and
  22 +      possibly gain authentication.  Fix by adding the check.
  23 +
  24
  25  Exim version 4.92
  26  -----------------
  27 --- a/src/auths/spa.c
  28 +++ b/src/auths/spa.c
  29 @@ -139,7 +139,7 @@ SPAAuthChallenge challenge;
  30  SPAAuthResponse  response;
  31  SPAAuthResponse  *responseptr = &response;
  32  uschar msgbuf[2048];
  33 -uschar *clearpass;
  34 +uschar *clearpass, *s;
  35
  36  /* send a 334, MS Exchange style, and grab the client's request,
  37  unless we already have it via an initial response. */
  38 @@ -197,6 +197,13 @@ that causes failure if the size of msgbu
  39    char *p = ((char*)responseptr) + IVAL(&responseptr->uUser.offset,0);
  40    int len = SVAL(&responseptr->uUser.len,0)/2;
  41
  42 +  if (p + len*2 >= CS (responseptr+1))
  43 +    {
  44 +    DEBUG(D_auth)
  45 +      debug_printf("auth_spa_server(): bad uUser spec in response\n");
  46 +    return FAIL;
  47 +    }
  48 +
  49    if (len + 1 >= sizeof(msgbuf)) return FAIL;
  50    for (i = 0; i < len; ++i)
  51      {
  52 @@ -245,14 +252,17 @@ spa_smb_nt_encrypt (clearpass, challenge
  53
  54  /* compare NT hash (LM may not be available) */
  55
  56 -if (memcmp(ntRespData,
  57 -      ((unsigned char*)responseptr)+IVAL(&responseptr->ntResponse.offset,0),
  58 -      24) == 0)
  59 -  /* success. we have a winner. */
  60 +s = (US responseptr) + IVAL(&responseptr->ntResponse.offset,0);
  61 +if (s + 24 >= US (responseptr+1))
  62    {
  63 -  return auth_check_serv_cond(ablock);
  64 +  DEBUG(D_auth)
  65 +    debug_printf("auth_spa_server(): bad ntRespData spec in response\n");
  66 +  return FAIL;
  67    }
  68
  69 +if (memcmp(ntRespData, s, 24) == 0)
  70 +  return auth_check_serv_cond(ablock); /* success. we have a winner. */
  71 +
  72    /* Expand server_condition as an authorization check (PH) */
  73
  74  return FAIL;