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53 lines
2.7 KiB
Diff
53 lines
2.7 KiB
Diff
IMPORTANT!
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This distribution includes a patch (already applied), that updates
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Kerberos' key generation. The gist of the patch is to replace calls
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to des_random_key() with calls to des_new_random_key().
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The primary difference is that des_random_key() uses a seeding
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technique which is predictable and therefore vulnerable.
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des_new_random_key() uses a feedback mechanism based on the Data
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Encryption Standard (DES) and is seeded with a secret (and therefore
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unknown to an attacker) value. This value is the database master
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key, which is a convenient secret value.
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This patch uses the new_rnd_key.c key module (which contains the
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definition and code for des_new_random_key()). It has been part of
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the standard Version 4 distribution since 1992 (and was recreated
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for FreeBSD in 1995). This is used in the MIT admin server (the
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primary error at MIT was not upgrading all of Kerberos to use this
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newer generator. This patch finishes the job).
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In addition to the patch for the Kerberos distribution this
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distribution also contains a program for changing critical system keys
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(namely the "krbtgt" and "changepw.kerberos" keys). When you
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originally built your Kerberos database these keys were chosen at
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random, using the vulnerable version of the kerberos random number
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generator. Therefore it is possible for an attacker to mount an attack
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to guess these values. If an attacker can determine the key for the
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"krbtgt" ticket, they can construct tickets claiming to be any
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kerberos principal. Similarly if an attacker can obtain the
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"changepw.kerberos" key, they can change anyone's password.
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The new "fix_kdb_keys(8)" program, which you run on the KDC
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server, will change these critical keys to new values using the
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newer random number generator. IMPORTANT: When you run fix_kdb_keys,
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all outstanding ticket granting tickets will immediately become
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invalid. This will be disruptive to your user community. We recommend
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that you either do this late at night or early in the morning before
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most users have logged in. Alternatively pre-announce a definitive
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time when you will run the program and inform your users that they
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will have to get new tickets at that time (using either "kinit" or
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simply by logging out and then in again).
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NOTE: The only client program modified is "ksrvutil" which is used
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to generate new server keys. All other client/server programs are
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unaffected. End users do *not* need to obtain new versions of
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programs that use Kerberos. This is because most random number
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generation in the Kerberos system is done on the KDC system.
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After getting these sources, type "make world" at the toplevel of
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your source tree. This will, among other things, build the fix_kdb_keys
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program. This is not necessary if you have already got prebuilt
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binaries with this distribution.
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