ZDI-07-052: Multiple Kerberos Implementations Authentication Context
            Stack Overflow Vulnerability
http://www.zerodayinitiative.com/advisories/ZDI-07-052.html
September  12, 2007

-- CVE ID:
CVE-2007-3999

-- Affected Vendor:
MIT

-- Affected Products:
MIT Kerberos krb5-1.6.2

-- TippingPoint(TM) IPS Customer Protection:
TippingPoint IPS customers have been protected against this
vulnerability since September  7, 2007 by Digital Vaccine protection
filter ID 5503. For further product information on the TippingPoint IPS:

    http://www.tippingpoint.com 

-- Vulnerability Details:
This vulnerability allows remote attackers to execute arbitrary code on
vulnerable installations of MIT Kerberos. Authentication is not
required to exploit this vulnerability.

The specific flaw exists in the svcauth_gss_validate() function. By
sending a large authentication context over RPC, a stack based buffer
overflow occurs, resulting in a situation allowing for remote code
execution.

The vulnerable line of the function is: 
   memcpy((caddr_t)buf, oa->oa_base, oa->oa_length);

If 128 < oa->oa_length < 400, the exploitable situation occurs. Over
400 bytes is caught during a separate check for MAX_AUTH_SIZE earlier
in the RPC packet decoding process.

-- Vendor Response:
MIT has issued an update to correct this vulnerability. More details can
be found at:

http://web.mit.edu/kerberos/advisories/MITKRB5-SA-2007-006.txt

-- Disclosure Timeline:
2007.07.20 - Vulnerability reported to vendor
2007.09.07 - Digital Vaccine released to TippingPoint customers
2007.09.07 - Coordinated public release of advisory

-- Credit:
This vulnerability was discovered by Tenable Network Security.

-- About the Zero Day Initiative (ZDI):
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(ZDI) represents a best-of-breed model for rewarding security
researchers for responsibly disclosing discovered vulnerabilities.

Researchers interested in getting paid for their security research
through the ZDI can find more information and sign-up at:

    http://www.zerodayinitiative.com

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