[UNIX] kcheckpass Insecure File Operation

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kcheckpass Insecure File Operation
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SUMMARY

<http://kde.org> kcheckpass - KDE pam client that allows you to auth as a
specified user without actually doing anything as that user.

kcheckpass creates lockfile in an insecure way, exploiting this
vulnerability allows malicious attacker to create a world writable file
anywhere.

DETAILS

Vulnerable Systems:
* kdebase versions 3.2.0 to 3.4.2

kcheckpass is a utility used to authenticate users. It's used by tools
such as kscreensaver. The code that's used to create a lockfile doesn't
check for or sets the umask. Besides the umask problem it will also
happily follow symlinks, as shown by the following code snippet:
..
sprintf(fname, "/var/lock/kcheckpass.%d", uid);
if ((lfd = open(fname, O_RDWR | O_CREAT)) >= 0) {
}
..

In order for an attacker to be able to exploit this /var/lock would have
to be world writable and kcheckpass would have to be suid. When these
conditions are met an attacker can create a world writable file anywhere.

When properly exploited users can gain root privileges (given that the
previously mentioned conditions are met).

CVE Information:
<http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2005-2494>
CAN-2005-2494

ADDITIONAL INFORMATION

The information has been provided by <mailto:advisories@suresec.org> Ilja
van Sprundel.
The original article can be found at:
<http://www.suresec.org/advisories/adv6.pdf>
http://www.suresec.org/advisories/adv6.pdf

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