krb5 commit: Fix LDAP key data segmentation [CVE-2014-4345]

[Greg Hudson]

https://github.com/krb5/krb5/commit/81c332e29f10887c6b9deb065f81ba259f4c7e03
commit 81c332e29f10887c6b9deb065f81ba259f4c7e03
Author: Tomas Kuthan <tkuthan at gmail.com>
Date:   Fri Aug 1 15:25:50 2014 +0200

    Fix LDAP key data segmentation [CVE-2014-4345]
    
    For principal entries having keys with multiple kvnos (due to use of
    -keepold), the LDAP KDB module makes an attempt to store all the keys
    having the same kvno into a single krbPrincipalKey attribute value.
    There is a fencepost error in the loop, causing currkvno to be set to
    the just-processed value instead of the next kvno.  As a result, the
    second and all following groups of multiple keys by kvno are each
    stored in two krbPrincipalKey attribute values.  Fix the loop to use
    the correct kvno value.
    
    CVE-2014-4345:
    
    In MIT krb5, when kadmind is configured to use LDAP for the KDC
    database, an authenticated remote attacker can cause it to perform an
    out-of-bounds write (buffer overrun) by performing multiple cpw
    -keepold operations.  An off-by-one error while copying key
    information to the new database entry results in keys sharing a common
    kvno being written to different array buckets, in an array whose size
    is determined by the number of kvnos present.  After sufficient
    iterations, the extra writes extend past the end of the
    (NULL-terminated) array.  The NULL terminator is always written after
    the end of the loop, so no out-of-bounds data is read, it is only
    written.
    
    Historically, it has been possible to convert an out-of-bounds write
    into remote code execution in some cases, though the necessary
    exploits must be tailored to the individual application and are
    usually quite complicated.  Depending on the allocated length of the
    array, an out-of-bounds write may also cause a segmentation fault
    and/or application crash.
    
        CVSSv2 Vector: AV:N/AC:M/Au:S/C:C/I:C/A:C/E:POC/RL:OF/RC:C
    
    [ghudson at mit.edu: clarified commit message]
    [kaduk at mit.edu: CVE summary, CVSSv2 vector]
    
    ticket: 7980 (new)
    target_version: 1.12.2
    tags: pullup

 src/plugins/kdb/ldap/libkdb_ldap/ldap_principal2.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/src/plugins/kdb/ldap/libkdb_ldap/ldap_principal2.c b/src/plugins/kdb/ldap/libkdb_ldap/ldap_principal2.c
index ce851ea..df5934c 100644
--- a/src/plugins/kdb/ldap/libkdb_ldap/ldap_principal2.c
+++ b/src/plugins/kdb/ldap/libkdb_ldap/ldap_principal2.c
@@ -456,7 +456,8 @@ krb5_encode_krbsecretkey(krb5_key_data *key_data_in, int n_key_data,
             j++;
             last = i + 1;
 
-            currkvno = key_data[i].key_data_kvno;
+            if (i < n_key_data - 1)
+                currkvno = key_data[i + 1].key_data_kvno;
         }
     }
     ret[num_versions] = NULL;