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Home » Hacking News » RHSA-2002:132-14-Updated util-linux package fixes password locking race

RHSA-2002:132-14-Updated util-linux package fixes password locking race

by Nikola Strahija on July 29th, 2002 A locally exploitable vulnerability is present in the util-linux package shipped with Red Hat Linux

2. Relevant releases/architectures:

Red Hat Linux 6.2 - alpha, i386, sparc

Red Hat Linux 7.0 - alpha, i386

Red Hat Linux 7.1 - alpha, i386, ia64

Red Hat Linux 7.2 - i386, ia64

Red Hat Linux 7.3 - i386

3. Problem description:

The util-linux package contains a large variety of low-level system
utilities that are necessary for a Linux system to function. The 'chfn'
utility included in this package allows users to modify personal
information stored in the system-wide password file, /etc/passwd. In order
to modify this file, this application is installed setuid root.

Under certain conditions, a carefully crafted attack sequence can be
performed to exploit a complex file locking and modification race present
in this utility allowing changes to be made to /etc/passwd.

In order to successfully exploit the vulnerability and perform privilege
escalation there is a need for a minimal administrator interaction.
Additionally, the password file must be over 4 kilobytes, and the local
attackers entry must not be in the last 4 kilobytes of the password file.

The Common Vulnerabilities and Exposures project ( has
assigned the name CAN-2002-0638 to this issue.

An interim workaround is to remove setuid flags from /usr/bin/chfn and
/usr/bin/chsh. All users of Red Hat Linux should update to the errata
util-linux packages which contain a patch to correct this vulnerability.

Many thanks to Michal Zalewski of Bindview for alerting us to this issue.

4. Solution:

Before applying this update, make sure all previously released errata
relevant to your system have been applied.

To update all RPMs for your particular architecture, run:

rpm -Fvh [filenames]

where [filenames] is a list of the RPMs you wish to upgrade. Only those
RPMs which are currently installed will be updated. Those RPMs which are
not installed but included in the list will not be updated. Note that you
can also use wildcards (*.rpm) if your current directory *only* contains
the desired RPMs.

Please note that this update is also available via Red Hat Network. Many
people find this an easier way to apply updates. To use Red Hat Network,
launch the Red Hat Update Agent with the following command:


This will start an interactive process that will result in the appropriate
RPMs being upgraded on your system.

5. Bug IDs fixed ( for more info):

6. RPMs required:

Red Hat Linux 6.2:





Red Hat Linux 7.0:




Red Hat Linux 7.1:





Red Hat Linux 7.2:




Red Hat Linux 7.3:



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