Vulnerability Note VU#365313

MIT Kerberos kadmind RPC library gssrpc__svcauth_unix() integer conversion error

Overview

The MIT Kerberos administration daemon (kadmind) contains an integer conversion error vulnerability, which may allow a remote, unauthenticated attacker to execute arbitrary code or cause a denial of service.

I. Description

The gssrpc__svcauth_unix() function used by the Kerberos administration daemon contains an integer conversion error. This vulnerability may cause a stack buffer overflow that could allow a remote, authenticated user to execute arbitrary code. According to MIT krb5 Security Advisory MITKRB5-SA-2007-004:

The function gssrpc__svcauth_unix() in src/lib/rpc/svc_auth_unix.c stores an unsigned integer obtained from IXDR_GET_U_LONG into a signed integer variable "str_len". Subsequently, it checks that "str_len" is less than MAX_MACHINE_NAME, which will always be true of "str_len" is negative, which can happen when a large unsigned integer is converted to a signed integer. Once the length check succeeds, gssrpc__svcauth_unix() calls memmove() with a length of "str_len" with the target in a stack buffer.

This vulnerability is believed to be difficult to exploit because the memmove() implementation receives a very large number (a negative integer converted to a large unsigned value), which will almost certainly cause some sort of memory access fault prior to returning. This probably avoids any usage of the corrupted return address in the overwritten stack frame. Note that some (perhaps unlikely) memmove() implementations may call other procedures and thus may be vulnerable to corrupted return addresses.

Note that this issue affects all releases of MIT krb5 up to and including krb5-1.6.1. Third-party applications using the MIT krb5 RPC library or other RPC libraries derived from SunRPC may also be vulnerable. MIT has been provided with proof-of-concept exploit code that causes a denial of service, but it's not clear whether the exploit code is publicly available yet.

This vulnerability occurred as a result of failing to comply with rule INT31-C of the CERT C Programming Language Secure Coding Standard.

II. Impact

A remote, unauthenticated user may be able to execute arbitrary code on an affected system or cause the affected program to crash, resulting in a denial of service. Secondary impacts of code execution include complete compromise of the Kerberos key database.

III. Solution

Apply a patch

A patch can be obtained from MIT krb5 Security Advisory MITKRB5-SA-2007-004. MIT also states that this will be addressed in the upcoming krb5-1.6.2 and krb5-1.5.4 releases. Please check with your vendor for third-party product updates.

Systems Affected

Vendor	Status	Date Updated
Apple Computer, Inc.	Unknown	18-Jun-2007
AttachmateWRQ, Inc.	Unknown	18-Jun-2007
Conectiva Inc.	Unknown	18-Jun-2007
Cray Inc.	Unknown	18-Jun-2007
CyberSafe, Inc.	Not Vulnerable	18-Jun-2007
Debian GNU/Linux	Vulnerable	30-Jul-2007
EMC Corporation	Unknown	18-Jun-2007
Engarde Secure Linux	Unknown	18-Jun-2007
F5 Networks, Inc.	Unknown	18-Jun-2007
Fedora Project	Unknown	18-Jun-2007
FreeBSD, Inc.	Unknown	18-Jun-2007
Fujitsu	Unknown	18-Jun-2007
Gentoo Linux	Unknown	18-Jun-2007
Hewlett-Packard Company	Unknown	18-Jun-2007
Hitachi	Unknown	18-Jun-2007
IBM Corporation	Unknown	18-Jun-2007
IBM Corporation (zseries)	Unknown	18-Jun-2007
IBM eServer	Unknown	18-Jun-2007
Immunix Communications, Inc.	Unknown	18-Jun-2007
Ingrian Networks, Inc.	Unknown	18-Jun-2007
Juniper Networks, Inc.	Not Vulnerable	26-Jun-2007
KTH Kerberos Team	Unknown	18-Jun-2007
Mandriva, Inc.	Vulnerable	27-Jun-2007
Microsoft Corporation	Not Vulnerable	19-Jun-2007
MIT Kerberos Development Team	Unknown	13-Jun-2007
MontaVista Software, Inc.	Unknown	18-Jun-2007
NEC Corporation	Unknown	18-Jun-2007
NetBSD	Unknown	18-Jun-2007
Network Appliance, Inc.	Not Vulnerable	27-Jun-2007
Nokia	Unknown	18-Jun-2007
Novell, Inc.	Unknown	18-Jun-2007
Openwall GNU/*/Linux	Unknown	18-Jun-2007
QNX, Software Systems, Inc.	Unknown	18-Jun-2007
Red Hat, Inc.	Vulnerable	26-Jun-2007
Silicon Graphics, Inc.	Unknown	18-Jun-2007
Slackware Linux Inc.	Unknown	18-Jun-2007
Sony Corporation	Unknown	18-Jun-2007
Sun Microsystems, Inc.	Not Vulnerable	28-Jun-2007
SUSE Linux	Unknown	18-Jun-2007
The SCO Group	Unknown	18-Jun-2007
Trustix Secure Linux	Unknown	18-Jun-2007
Turbolinux	Unknown	18-Jun-2007
Ubuntu	Vulnerable	27-Jun-2007
Unisys	Unknown	18-Jun-2007
Wind River Systems, Inc.	Unknown	18-Jun-2007

References

https://www.securecoding.cert.org/confluence/display/seccode/INT31-C.+Ensure+that+integer+conversions+do+not+result+in+lost+or+misinterpreted+data
http://web.mit.edu/kerberos/www/advisories/MITKRB5-SA-2007-004.txt
http://www.ubuntu.com/usn/usn-477-1
http://www.mandriva.com/security/advisories?name=MDKSA-2007:137
http://secunia.com/advisories/25800/
http://secunia.com/advisories/26033/
http://docs.info.apple.com/article.html?artnum=306172

Credit

Thanks to MIT for reporting this vulnerability, who in turn credit Wei Wang of McAfee Avert Labs.

This document was written by Will Dormann.

Other Information

Date Public	06/26/2007
Date First Published	06/26/2007 02:59:11 PM
Date Last Updated	08/08/2007
CERT Advisory
CVE Name	CVE-2007-2443
Metric	5.40
Document Revision	12