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Category:   Application (Security)  >   OpenSSH Vendors:   OpenSSH.org
(OpenBSD Issues Patch) Re: OpenSSH Buffer Overflow in Kerberos Ticket and AFS Token Processing Lets Local Users Execute Arbitrary Code With Root Level Permissions
SecurityTracker Alert ID:  1004137
SecurityTracker URL:  http://securitytracker.com/id/1004137
CVE Reference:   GENERIC-MAP-NOMATCH   (Links to External Site)
Date:  Apr 23 2002
Impact:   Execution of arbitrary code via local system, Root access via local system
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): 2.2.0 - 3.1.0
Description:   A buffer overflow vulnerability has been reported in OpenSSH server. A local user can trigger the overflow to gain root level operating system access.

It is reported that the flaw exists in OpenSSH's Kerberos Ticket Granting Ticket (TGT) and/or AFS Token passing. According to the report, the GETSTRING macro in the radix_to_creds() function in the 'radix.c' file contains unchecked buffer operations. The affected buffers are:

creds->service
creds->instance
creds->realm
creds->pinst

A local user can apparently send a specially crafted, malformed request to:

1. pass Kerberos IV TGT
2. pass AFS Token

Apparently, the code clears the CREDENTIALS structure end of the auth_krb4_tgt() function (in file 'auth_krb4.c') but fails to clear user-supplied contents from the temp[] buffer in the radix_to_creds() function. When the server decodes the Kerberos ticket, the overflow can be triggered to cause arbitrary code to be executed with root level privileges.

The author of the report has provided a URL for some demonstration exploit code:

http://www.freeweb.hu/mantra/04_2002/tgt-x86Linux.tar.gz

Impact:   A remote user can execute arbitrary code on the server with root level privleges.
Solution:   A source code patch for OpenBSD is available to fix the problem:

ftp://ftp.openbsd.org/pub/OpenBSD/patches/3.0/common/019_sshafs.patch

Vendor URL:  www.openssh.org/ (Links to External Site)
Cause:   Boundary error
Underlying OS:  UNIX (OpenBSD)
Underlying OS Comments:  OpenBSD 3.0

Message History:   This archive entry is a follow-up to the message listed below.
Apr 19 2002 OpenSSH Buffer Overflow in Kerberos Ticket and AFS Token Processing Lets Local Users Execute Arbitrary Code With Root Level Permissions



 Source Message Contents

Subject:  OpenBSD Security Fix


019: SECURITY FIX: April 22, 2002

A local user can gain super-user privileges due to a buffer overflow in
sshd(8) if AFS has been configured on the system or if
KerberosTgtPassing or AFSTokenPassing has been enabled in the
sshd_config file. Ticket and token passing is not enabled by default.

A source code patch exists which remedies the problem:

ftp://ftp.openbsd.org/pub/OpenBSD/patches/3.0/common/019_sshafs.patch


 
 


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