Hewlett Packard HP-UX Remote pfs_mountd.rpc Buffer Overflow Vulnerability

iDefense Security Advisory 04.12.07
http://labs.idefense.com/intelligence/vulnerabilities/
Apr 12, 2007

I. BACKGROUND

PFS (the Portable File System) allows mounting of ISO 9660, High Sierra,
and Rock Ridge (ISO 9660 with Rock Ridge extensions) CD-ROM disks. The
daemon pfs_mountd.rpc is an RPC extension that is launched along with
pfsd in order to allow the easy mounting of these file systems under
HP-UX. It is remotely accessible over TCP and UDP.

II. DESCRIPTION

Remote exploitation of a buffer overflow vulnerability in pfs_mountd.rpc
included in multiple versions of Hewlett Packard Co. HP-UX allows for
remote root access.

If a remote user sends two specially crafted packets over UDP, the
buffer overflow is triggered. One must first send a call to procedure
5, and soon thereafter send the actual payload to procedure 2. Due to
the closed nature of the pfs_mountd.rpc protocol specification, it is
unclear at this time what functions the respective procedures actually
perform.

III. ANALYSIS

The seriousness of this vulnerability is reduced by the fact that in
most cases an attacker will only have one chance at exploitation until
an administrator restarts the crashed daemon after a failed attempt.
However, the attack is functional over UDP, thus allowing an attacker
to completely spoof the attack, possibly even making it appear from
inside a trusted network.

IV. DETECTION

iDefense has confirmed the existence of this vulnerability in HP-UX
11.11i. It is suspected that previous versions are also vulnerable.

V. WORKAROUND

Adding firewall rules may not be enough to stop this attack due to the
fact that it can be spoofed.

VI. VENDOR RESPONSE

Hewlett-Packard discontinued support for the PFS on March 1st, 2004. As
a solution to this vulnerability, Hewlett-Packard recommends
discontinuing the use of PFS. More information is available from HP
Security Bulletin HPSBUX02203 at the following URL.

http://www1.itrc.hp.com/service/cki/docDisplay.do?docId=c00913684

VII. CVE INFORMATION

A Mitre Corp. Common Vulnerabilities and Exposures (CVE) number has not
been assigned yet.

VIII. DISCLOSURE TIMELINE

10/25/2004  Initial vendor notification
10/25/2004  Initial vendor response
12/19/2005  Second vendor notification
01/30/2007  Third vendor notification
04/12/2007  Coordinated public disclosure

IX. CREDIT

This vulnerability was discovered by iDefense Labs.

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X. LEGAL NOTICES

Copyright © 2007 iDefense, Inc.

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