RHSA-2013:0504 - Security Advisory

Topic

Updated dhcp packages that fix one security issue and two bugs are now
available for Red Hat Enterprise Linux 6.

The Red Hat Security Response Team has rated this update as having low
security impact. A Common Vulnerability Scoring System (CVSS) base score,
which gives a detailed severity rating, is available from the CVE link in
the References section.

Description

The dhcp packages provide the Dynamic Host Configuration Protocol (DHCP)
that allows individual devices on an IP network to get their own network
configuration information, including an IP address, a subnet mask, and a
broadcast address.

A flaw was found in the way the dhcpd daemon handled the expiration time of
IPv6 leases. If dhcpd's configuration was changed to reduce the default
IPv6 lease time, lease renewal requests for previously assigned leases
could cause dhcpd to crash. (CVE-2012-3955)

This update also fixes the following bugs:

• Prior to this update, the DHCP server discovered only the first IP

address of a network interface if the network interface had more than one
configured IP address. As a consequence, the DHCP server failed to
restart if the server was configured to serve only a subnet of the
following IP addresses. This update modifies network interface addresses
discovery code to find all addresses of a network interface. The DHCP
server can also serve subnets of other addresses. (BZ#803540)

• Prior to this update, the dhclient rewrote the /etc/resolv.conf file

with backup data after it was stopped even when the PEERDNS flag was set
to "no" before shut down if the configuration file was changed while the
dhclient ran with PEERDNS=yes. This update removes the backing up and
restoring functions for this configuration file from the dhclient-script.
Now, the dhclient no longer rewrites the /etc/resolv.conf file when
stopped. (BZ#824622)

All users of DHCP are advised to upgrade to these updated packages, which
fix these issues. After installing this update, all DHCP servers will be
restarted automatically.

Solution

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

This update is available via the Red Hat Network. Details on how to
use the Red Hat Network to apply this update are available at
https://access.redhat.com/knowledge/articles/11258

Affected Products

• Red Hat Enterprise Linux Server 6 x86_64
• Red Hat Enterprise Linux Server 6 i386
• Red Hat Enterprise Linux Server - Extended Life Cycle Support 6 x86_64
• Red Hat Enterprise Linux Server - Extended Life Cycle Support 6 i386
• Red Hat Enterprise Linux Workstation 6 x86_64
• Red Hat Enterprise Linux Workstation 6 i386
• Red Hat Enterprise Linux Desktop 6 x86_64
• Red Hat Enterprise Linux Desktop 6 i386
• Red Hat Enterprise Linux for IBM z Systems 6 s390x
• Red Hat Enterprise Linux for Power, big endian 6 ppc64
• Red Hat Enterprise Linux for Scientific Computing 6 x86_64
• Red Hat Enterprise Linux Server from RHUI 6 x86_64
• Red Hat Enterprise Linux Server from RHUI 6 i386
• Red Hat Enterprise Linux Server - Extended Life Cycle Support (for IBM z Systems) 6 s390x

Fixes

• BZ - 803540 - DHCP server fails to start if the subnet is not the primary subnet for a device
• BZ - 824622 - dhclient-script should honor PEERDNS on quit
• BZ - 856766 - CVE-2012-3955 dhcp: reduced expiration time of an IPv6 lease may cause dhcpd to crash

CVEs

• CVE-2012-3955

References

• https://access.redhat.com/security/updates/classification/#low