[UNIX] Multiple Kerberos Implementations Authentication Context Stack Overflow Vulnerability

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Multiple Kerberos Implementations Authentication Context Stack Overflow
Vulnerability
------------------------------------------------------------------------


SUMMARY

A vulnerability allows remote attackers to execute arbitrary code on
vulnerable installations of MIT Kerberos. Authentication is not required
to exploit this vulnerability.

DETAILS

Vulnerable Systems:
* MIT Kerberos krb5-1.6.2

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>
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


ADDITIONAL INFORMATION

The information has been provided by <mailto:zdi-disclosures@xxxxxxxx>
The Zero Day Initiative (ZDI).
The original article can be found at:
<http://www.zerodayinitiative.com/advisories/ZDI-07-052.html>
http://www.zerodayinitiative.com/advisories/ZDI-07-052.html



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