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Category:   Application (Security)  >   Kerberos Vendors:   MIT
(HP Issues Fix for OpenVMS) MIT Kerberos Checksum Handling Errors May Let Remote or Remote Authenticated Users Forge/Modify Certain Data
SecurityTracker Alert ID:  1025497
SecurityTracker URL:  http://securitytracker.com/id/1025497
CVE Reference:   CVE-2010-1323   (Links to External Site)
Date:  May 6 2011
Impact:   Modification of authentication information, Modification of system information
Fix Available:  Yes  Vendor Confirmed:  Yes  

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:   HP has issued a fix (3.2) for CVE-2010-1323 for OpenVMS Alpha and OpenVMS Integrity servers, available at:

http://h71000.www7.hp.com/openvms/products/kerberos

The HP advisory is available at:

http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?objectID=c02824440

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

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



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