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Category:   Application (Security)  >   Kerberos Vendors:   MIT
(Red Hat Issues Fix) MIT Kerberos Checksum Handling Errors May Let Remote or Remote Authenticated Users Forge/Modify Certain Data
SecurityTracker Alert ID:  1024805
SecurityTracker URL:  http://securitytracker.com/id/1024805
CVE Reference:   CVE-2010-1323, CVE-2010-1324, CVE-2010-4020   (Links to External Site)
Date:  Dec 1 2010
Impact:   Modification of authentication information, Modification of system information
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): 5-1.7, 5-1.8
Description:   Several vulnerabilities were reported in Kerberos. A remote or remote authenticated user can forge certain signatures and modify checksums.

The software incorrectly accepts an unkeyed checksum with DES session keys for version 2 (RFC 4121) of the GSS-API krb5 mechanism , an unkeyed checksum for PAC signatures, and RFC 3961 key-derivation checksums using RC4 keys when verifying the req-checksum in a KrbFastArmoredReq [CVE-2010-1324].

A remote user can forge GSS tokens if the targeted pre-existing application session uses a DES session key. A remote authenticated user can forge PACs when using a KDC that does not filter client-provided PAC data to obtain elevated privileges. A remote user can swap a client-issued KrbFastReq into a different KDC-REQ if the armor key is RC4 (1/256 chance).

The software incorrectly accepts unkeyed checksums in the SAM-2 preauthentication challenge and incorrectly accepts RFC 3961 key-derivation checksums using RC4 keys when verifying KRB-SAFE messages [CVE-2010-1323].

A remote user can modify a SAM-2 challenge, affecting the prompt text seen by the user or the kind of response sent to the KDC. A remote user can forge KRB-SAFE messages in an application protocol if the targeted pre-existing session uses an RC4 session key.

The software incorrectly accepts RFC 3961 key-derivation checksums using RC4 keys when verifying AD-SIGNEDPATH and AD-KDC-ISSUED authorization data [CVE-2010-4020].

A remote authenticated user that controls a legitimate service principal can forge the AD-SIGNEDPATH signature if the TGT key is RC4 (1/256 chance). The remote user can use self-generated "evidence" tickets for S4U2Proxy instead of tickets obtained from the user or with S4U2Self. A remote authenticated user can forge AD-KDC-ISSUED signatures on authdata elements in tickets having an RC4 service key to gain elevated privileges.

The software (version krb5-1.7 only) may issue tickets not requested by a client, based on an attacker-chosen KrbFastArmoredReq [CVE-2010-4021].

A remote authenticated user that controls a legitimate service principal can obtain a valid service ticket to itself containing valid KDC-generated authorization data for a client whose TGS-REQ it has intercepted. The user can then use this ticket for S4U2Proxy to impersonate the targeted client even if the client never authenticated to the subverted service.

Impact:   A remote or remote authenticated user can forge certain signatures and modify checksums.
Solution:   Red Hat has issued a fix for CVE-2010-1323, CVE-2010-1324, and CVE-2010-4020.

The Red Hat advisory is available at:

https://rhn.redhat.com/errata/RHSA-2010-0925.html

Vendor URL:  web.mit.edu/kerberos/advisories/MITKRB5-SA-2010-007.txt (Links to External Site)
Cause:   Access control error, Authentication error
Underlying OS:  Linux (Red Hat Enterprise)
Underlying OS Comments:  6

Message History:   This archive entry is a follow-up to the message listed below.
Nov 30 2010 MIT Kerberos Checksum Handling Errors May Let Remote or Remote Authenticated Users Forge/Modify Certain Data



 Source Message Contents

Subject:  [RHSA-2010:0925-01] Important: krb5 security and bug fix update

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=====================================================================
                   Red Hat Security Advisory

Synopsis:          Important: krb5 security and bug fix update
Advisory ID:       RHSA-2010:0925-01
Product:           Red Hat Enterprise Linux
Advisory URL:      https://rhn.redhat.com/errata/RHSA-2010-0925.html
Issue date:        2010-11-30
CVE Names:         CVE-2010-1323 CVE-2010-1324 CVE-2010-4020 
=====================================================================

1. Summary:

Updated krb5 packages that fix multiple security issues and one bug are now
available for Red Hat Enterprise Linux 6.

The Red Hat Security Response Team has rated this update as having
important security impact. Common Vulnerability Scoring System (CVSS) base
scores, which give detailed severity ratings, are available for each
vulnerability from the CVE links in the References section.

2. Relevant releases/architectures:

Red Hat Enterprise Linux Desktop (v. 6) - i386, x86_64
Red Hat Enterprise Linux Desktop Optional (v. 6) - i386, x86_64
Red Hat Enterprise Linux HPC Node (v. 6) - x86_64
Red Hat Enterprise Linux HPC Node Optional (v. 6) - x86_64
Red Hat Enterprise Linux Server (v. 6) - i386, ppc64, s390x, x86_64
Red Hat Enterprise Linux Workstation (v. 6) - i386, x86_64

3. Description:

Kerberos is a network authentication system which allows clients and
servers to authenticate to each other using symmetric encryption and a
trusted third party, the Key Distribution Center (KDC).

Multiple checksum validation flaws were discovered in the MIT Kerberos
implementation. A remote attacker could use these flaws to tamper with
certain Kerberos protocol packets and, possibly, bypass authentication or
authorization mechanisms and escalate their privileges. (CVE-2010-1323,
CVE-2010-1324, CVE-2010-4020)

Red Hat would like to thank the MIT Kerberos Team for reporting these
issues.

This update also fixes the following bug:

* When attempting to perform PKINIT pre-authentication, if the client had
more than one possible candidate certificate the client could fail to
select the certificate and key to use. This usually occurred if certificate
selection was configured to use the value of the keyUsage extension, or if
any of the candidate certificates did not contain a subjectAltName
extension. Consequently, the client attempted to perform pre-authentication
using a different (usually password-based) mechanism. (BZ#644825)

All krb5 users should upgrade to these updated packages, which contain
backported patches to correct these issues. After installing the updated
packages, the krb5kdc daemon will be restarted automatically.

4. Solution:

Before applying this update, make sure all previously-released errata
relevant to your system have been applied.

This update is available via the Red Hat Network. Details on how to
use the Red Hat Network to apply this update are available at
http://kbase.redhat.com/faq/docs/DOC-11259

5. Bugs fixed (http://bugzilla.redhat.com/):

644825 - 'kinit' with smart card login fails to authenticate to the kdc using the cert and its private key.
648674 - CVE-2010-1324 krb5: multiple checksum handling vulnerabilities (MITKRB5-SA-2010-007)
648734 - CVE-2010-1323 krb5: incorrect acceptance of certain checksums (MITKRB5-SA-2010-007)
648735 - CVE-2010-4020 krb5: krb5 may accept authdata checksums with low-entropy derived keys (MITKRB5-SA-2010-007)

6. Package List:

Red Hat Enterprise Linux Desktop (v. 6):

Source:
ftp://ftp.redhat.com/pub/redhat/linux/enterprise/6Client/en/os/SRPMS/krb5-1.8.2-3.el6_0.3.src.rpm

i386:
krb5-debuginfo-1.8.2-3.el6_0.3.i686.rpm
krb5-libs-1.8.2-3.el6_0.3.i686.rpm
krb5-pkinit-openssl-1.8.2-3.el6_0.3.i686.rpm
krb5-workstation-1.8.2-3.el6_0.3.i686.rpm

x86_64:
krb5-debuginfo-1.8.2-3.el6_0.3.i686.rpm
krb5-debuginfo-1.8.2-3.el6_0.3.x86_64.rpm
krb5-libs-1.8.2-3.el6_0.3.i686.rpm
krb5-libs-1.8.2-3.el6_0.3.x86_64.rpm
krb5-pkinit-openssl-1.8.2-3.el6_0.3.x86_64.rpm
krb5-workstation-1.8.2-3.el6_0.3.x86_64.rpm

Red Hat Enterprise Linux Desktop Optional (v. 6):

Source:
ftp://ftp.redhat.com/pub/redhat/linux/enterprise/6Client/en/os/SRPMS/krb5-1.8.2-3.el6_0.3.src.rpm

i386:
krb5-debuginfo-1.8.2-3.el6_0.3.i686.rpm
krb5-devel-1.8.2-3.el6_0.3.i686.rpm
krb5-server-1.8.2-3.el6_0.3.i686.rpm
krb5-server-ldap-1.8.2-3.el6_0.3.i686.rpm

x86_64:
krb5-debuginfo-1.8.2-3.el6_0.3.i686.rpm
krb5-debuginfo-1.8.2-3.el6_0.3.x86_64.rpm
krb5-devel-1.8.2-3.el6_0.3.i686.rpm
krb5-devel-1.8.2-3.el6_0.3.x86_64.rpm
krb5-server-1.8.2-3.el6_0.3.x86_64.rpm
krb5-server-ldap-1.8.2-3.el6_0.3.i686.rpm
krb5-server-ldap-1.8.2-3.el6_0.3.x86_64.rpm

Red Hat Enterprise Linux HPC Node (v. 6):

Source:
ftp://ftp.redhat.com/pub/redhat/linux/enterprise/6ComputeNode/en/os/SRPMS/krb5-1.8.2-3.el6_0.3.src.rpm

x86_64:
krb5-debuginfo-1.8.2-3.el6_0.3.i686.rpm
krb5-debuginfo-1.8.2-3.el6_0.3.x86_64.rpm
krb5-libs-1.8.2-3.el6_0.3.i686.rpm
krb5-libs-1.8.2-3.el6_0.3.x86_64.rpm

Red Hat Enterprise Linux HPC Node Optional (v. 6):

Source:
ftp://ftp.redhat.com/pub/redhat/linux/enterprise/6ComputeNode/en/os/SRPMS/krb5-1.8.2-3.el6_0.3.src.rpm

x86_64:
krb5-debuginfo-1.8.2-3.el6_0.3.i686.rpm
krb5-debuginfo-1.8.2-3.el6_0.3.x86_64.rpm
krb5-devel-1.8.2-3.el6_0.3.i686.rpm
krb5-devel-1.8.2-3.el6_0.3.x86_64.rpm
krb5-pkinit-openssl-1.8.2-3.el6_0.3.x86_64.rpm
krb5-server-1.8.2-3.el6_0.3.x86_64.rpm
krb5-server-ldap-1.8.2-3.el6_0.3.i686.rpm
krb5-server-ldap-1.8.2-3.el6_0.3.x86_64.rpm
krb5-workstation-1.8.2-3.el6_0.3.x86_64.rpm

Red Hat Enterprise Linux Server (v. 6):

Source:
ftp://ftp.redhat.com/pub/redhat/linux/enterprise/6Server/en/os/SRPMS/krb5-1.8.2-3.el6_0.3.src.rpm

i386:
krb5-debuginfo-1.8.2-3.el6_0.3.i686.rpm
krb5-devel-1.8.2-3.el6_0.3.i686.rpm
krb5-libs-1.8.2-3.el6_0.3.i686.rpm
krb5-pkinit-openssl-1.8.2-3.el6_0.3.i686.rpm
krb5-server-1.8.2-3.el6_0.3.i686.rpm
krb5-server-ldap-1.8.2-3.el6_0.3.i686.rpm
krb5-workstation-1.8.2-3.el6_0.3.i686.rpm

ppc64:
krb5-debuginfo-1.8.2-3.el6_0.3.ppc.rpm
krb5-debuginfo-1.8.2-3.el6_0.3.ppc64.rpm
krb5-devel-1.8.2-3.el6_0.3.ppc.rpm
krb5-devel-1.8.2-3.el6_0.3.ppc64.rpm
krb5-libs-1.8.2-3.el6_0.3.ppc.rpm
krb5-libs-1.8.2-3.el6_0.3.ppc64.rpm
krb5-pkinit-openssl-1.8.2-3.el6_0.3.ppc64.rpm
krb5-server-1.8.2-3.el6_0.3.ppc64.rpm
krb5-server-ldap-1.8.2-3.el6_0.3.ppc.rpm
krb5-server-ldap-1.8.2-3.el6_0.3.ppc64.rpm
krb5-workstation-1.8.2-3.el6_0.3.ppc64.rpm

s390x:
krb5-debuginfo-1.8.2-3.el6_0.3.s390.rpm
krb5-debuginfo-1.8.2-3.el6_0.3.s390x.rpm
krb5-devel-1.8.2-3.el6_0.3.s390.rpm
krb5-devel-1.8.2-3.el6_0.3.s390x.rpm
krb5-libs-1.8.2-3.el6_0.3.s390.rpm
krb5-libs-1.8.2-3.el6_0.3.s390x.rpm
krb5-pkinit-openssl-1.8.2-3.el6_0.3.s390x.rpm
krb5-server-1.8.2-3.el6_0.3.s390x.rpm
krb5-server-ldap-1.8.2-3.el6_0.3.s390.rpm
krb5-server-ldap-1.8.2-3.el6_0.3.s390x.rpm
krb5-workstation-1.8.2-3.el6_0.3.s390x.rpm

x86_64:
krb5-debuginfo-1.8.2-3.el6_0.3.i686.rpm
krb5-debuginfo-1.8.2-3.el6_0.3.x86_64.rpm
krb5-devel-1.8.2-3.el6_0.3.i686.rpm
krb5-devel-1.8.2-3.el6_0.3.x86_64.rpm
krb5-libs-1.8.2-3.el6_0.3.i686.rpm
krb5-libs-1.8.2-3.el6_0.3.x86_64.rpm
krb5-pkinit-openssl-1.8.2-3.el6_0.3.x86_64.rpm
krb5-server-1.8.2-3.el6_0.3.x86_64.rpm
krb5-server-ldap-1.8.2-3.el6_0.3.i686.rpm
krb5-server-ldap-1.8.2-3.el6_0.3.x86_64.rpm
krb5-workstation-1.8.2-3.el6_0.3.x86_64.rpm

Red Hat Enterprise Linux Workstation (v. 6):

Source:
ftp://ftp.redhat.com/pub/redhat/linux/enterprise/6Workstation/en/os/SRPMS/krb5-1.8.2-3.el6_0.3.src.rpm

i386:
krb5-debuginfo-1.8.2-3.el6_0.3.i686.rpm
krb5-devel-1.8.2-3.el6_0.3.i686.rpm
krb5-libs-1.8.2-3.el6_0.3.i686.rpm
krb5-pkinit-openssl-1.8.2-3.el6_0.3.i686.rpm
krb5-server-1.8.2-3.el6_0.3.i686.rpm
krb5-server-ldap-1.8.2-3.el6_0.3.i686.rpm
krb5-workstation-1.8.2-3.el6_0.3.i686.rpm

x86_64:
krb5-debuginfo-1.8.2-3.el6_0.3.i686.rpm
krb5-debuginfo-1.8.2-3.el6_0.3.x86_64.rpm
krb5-devel-1.8.2-3.el6_0.3.i686.rpm
krb5-devel-1.8.2-3.el6_0.3.x86_64.rpm
krb5-libs-1.8.2-3.el6_0.3.i686.rpm
krb5-libs-1.8.2-3.el6_0.3.x86_64.rpm
krb5-pkinit-openssl-1.8.2-3.el6_0.3.x86_64.rpm
krb5-server-1.8.2-3.el6_0.3.x86_64.rpm
krb5-server-ldap-1.8.2-3.el6_0.3.i686.rpm
krb5-server-ldap-1.8.2-3.el6_0.3.x86_64.rpm
krb5-workstation-1.8.2-3.el6_0.3.x86_64.rpm

These packages are GPG signed by Red Hat for security.  Our key and 
details on how to verify the signature are available from
https://www.redhat.com/security/team/key/#package

7. References:

https://www.redhat.com/security/data/cve/CVE-2010-1323.html
https://www.redhat.com/security/data/cve/CVE-2010-1324.html
https://www.redhat.com/security/data/cve/CVE-2010-4020.html
http://www.redhat.com/security/updates/classification/#important
http://web.mit.edu/Kerberos/advisories/MITKRB5-SA-2010-007.txt

8. Contact:

The Red Hat security contact is <secalert@redhat.com>.  More contact
details at https://www.redhat.com/security/team/contact/

Copyright 2010 Red Hat, Inc.
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