[Full-disclosure] [MU-200704-01] Pre-Authentication Vulnerability in Mac OS X RPC runtime library

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Pre-Authentication Vulnerability in Mac OS X RPC runtime library [MU-200704-01]
April 20, 2007

http://labs.musecurity.com/advisories.html

Affected Product/Versions:

Mac OS X v10.3.9,
Mac OS X Server v10.3.9,
Mac OS X v10.4.9,
Mac OS X Server v10.4.9

Product Overview:

"Portmap is a server that converts RPC program numbers into DARPA protocol
port numbers. It must be running in order to make RPC calls.

When an RPC server is started, it will register with the portmap the port
number it is listening to, and what RPC program numbers it is prepared to
serve. When a client wishes to make an RPC call to a given program number, it
will first contact portmap on the server machine to determine the port number
where RPC packets should be sent."

Vulnerability Details:

An integer overflow vulnerability exists in the RPC runtime library (libinfo)
that handles AUTH_UNIX authentication. By sending maliciously-crafted requests
to the any RPC service (portmap, mount, nfs, etc), a remote attacker can
trigger the overflow which may lead to arbitrary code execution as the
'daemon' user.

The problem is a signed integer issue in parsing XDR strings. In general an
XDR string contains a 4-byte big-endian length followed by the string. Any
length greater than 0x80000000 results in a negative length which is then
passed into a memcpy whose length can be controlled by the attacker.

The vulnerability can be triggered by sending the malicious AUTH_UNIX packets
to the NULL procedure of any enabled RPC service.

Vendor Response / Solution:

All users of RPC on OS X are recommended to immediately apply the security
updates available from the following URL:

http://docs.info.apple.com/article.html?artnum=61798

Mu Security would like to thank Apple for remediation of these
vulnerabilities.

History:

12/18/06 - First contact with the vendor
04/09/07 - Fix available for the vulnerabilities
04/20/07 - Advisory released

Credit:

This vulnerability was discovered by the Mu Security research team.

http://labs.musecurity.com/pgpkey.txt

Mu Security offers a new class of security analysis system, delivering a
rigorous and streamlined methodology for verifying the robustness and security
readiness of any IP-based product or application. Founded by the pioneers of
intrusion detection and prevention technology, Mu Security is backed by
preeminent venture capital firms that include Accel Partners, Benchmark
Capital and DAG Ventures. The company is headquartered in Sunnyvale, CA. For
more information, visit the company's website at http://www.musecurity.com.
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