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61 lines
3.0 KiB
Diff
61 lines
3.0 KiB
Diff
READ THIS ENTIRE FILE BEFORE PROCEEDING!
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This distribution contains a "diff" file suitable for using with the
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"patch" program to update your Kerberos (version 4) source tree. The
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gist of the patch is to replace calls to des_random_key() with calls
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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
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vulnerable. des_new_random_key() uses a feedback mechanism based on
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the Data Encryption Standard (DES) and is seeded with a secret (and
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therefore unknown to an attacker) value. This value is the database
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master key, which is a convenient secret value.
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This patch assumes that you have the new_rnd_key.c key module (which
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contains the definition and code for des_new_random_key()). It has
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been part of the standard Version 4 distribution since 1992 and is
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used in the admin server (our primary error at MIT was not upgrading
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all of Kerberos to use this newer generator. This patch finishes the
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job).
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In addition to the patch file 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 enclosed "fix_kdb_keys.c" (part of the patch file) program, which
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you run on the KDC server, will change these critical keys to new
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values using the newer random number generator. IMPORTANT: When you
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run fix_kdb_keys, all outstanding ticket granting tickets will
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immediately become invalid. This will be disruptive to your user
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community. We recommend that you either do this late at night or early
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in the morning before most users have logged in. Alternatively
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pre-announce a definitive time when you will run the program and
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inform your users that they will have to get new tickets at that time
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(using either "kinit" or simply by logging out and then in again).
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NOTE: The only client program modified is "ksrvutil" which is used to
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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 programs
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that use Kerberos. This is because most random number generation in
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the Kerberos system is done on the KDC system. By fixing kerberos.c
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you have repaired most of the damage.
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To install this patch copy patch_krb to the toplevel of your Kerberos
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source tree. Then type:
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patch -p0 <patch_krb
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This will install changes to various kerberos modules to upgrade them
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to use des_new_random_key(). It also will install a new program,
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"fix_kdb_keys.c." After the patch is complete type "make world" at the
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toplevel of your Kerberos source tree. This will, among other things,
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build the fix_kdb_keys program.
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