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Cisco IOS Malformed OSPF Packet Causes Reload
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SUMMARY
A Cisco device running Internetwork Operating System (IOS) and enabled for
the Open Shortest Path First (OSPF) protocol is vulnerable to a Denial of
Service (DoS) attack from a malformed OSPF packet. The OSPF protocol is
not enabled by default.
The vulnerability is only present in Cisco IOS release trains based on
12.0S, 12.2, and 12.3. Releases based on 12.0, 12.1 mainlines, and all
Cisco IOS images prior to 12.0 are not affected.
Cisco has made free software available to address this vulnerability.
There are workarounds available to mitigate the effects.
DETAILS
Vulnerable Products:
This vulnerability was introduced by a code change that was committed to
the 12.0S, 12.2, and 12.3 based release trains, causing these trains to be
vulnerable. All Cisco devices running a vulnerable release train and
running OSPF process are vulnerable.
Some release trains that are not vulnerable are explicitly listed below
for clarification. The release trains that are not mentioned below are not
vulnerable.
Release Train - Vulnerable Versions
10.x based releases - Not vulnerable
11.x based releases - Not vulnerable
12.0 based releases (except for 12.0.S based releases) - Not vulnerable
12.1 based releases - Not vulnerable
12.0.S - 12.0(22)S and later
12.0.SX - 12.0(23)SX and later
12.0.SY - 12.0(22)SY and later
12.0.SZ - 12.0(23)SZ and later
12.2 mainline - Not vulnerable
12.2.B - 12.2(15)B and later
12.2.BC - 12.2(15)BC and later
12.2.BX - 12.2(15)BX and later
12.2.BZ - 12.2(15)BZ and later
12.2.CX - 12.2(15)CX and later
12.2.EW - 12.2(18)EW and later
12.2.MC - 12.2(15)MC1 and later
12.2.S - 12.2(18)S and later
12.2.SE - 12.2(18)SE and later
12.2.SV - 12.2(18)SV and later
12.2.SW - 12.2(18)SW and later
12.2.SZ - 12.2(14)SZ and later
12.2.T - 12.2(15)T and later
12.2.YU - 12.2(11)YU and later
12.2.YV - 12.2(11)YV and later
12.2.ZD - 12.2(13)ZD and later
12.2.ZE - 12.2(13)ZE and later
12.2.ZF - 12.2(13)ZF and later
12.2.ZG - 12.2(13)ZG and later
12.2.ZH - 12.2(13)ZH and later
12.2.ZJ - 12.2(15)ZJ and later
12.2.ZK - 12.2(15)ZK and later
12.2.ZL - 12.2(15)ZL and later
12.2.ZN - 12.2(15)ZN and later
12.2.ZO - 12.2(15)ZO and later
12.3 - All 12.3 releases
12.3.B - All 12.3.B releases
12.3.BW - All 12.3.BW releases
12.3.T - All 12.3.T releases
12.3.XA - All 12.3.XA releases
12.3.XB - All 12.3.XB releases
12.3.XC - All 12.3.XC releases
12.3.XE - All 12.3.XE releases
A Cisco device that is running an OSPF process will have a line in the
configuration defining the process number, which can be seen by issuing
the command show running-config:
router ospf {process number}
To determine the software running on a Cisco product, log in to the device
and issue the show version command to display the system banner. Cisco IOS
software will identify itself as "Internetwork Operating System Software"
or simply "IOS." On the next line of output, the image name will be
displayed between parentheses, followed by "Version" and the Cisco IOS
release name. Other Cisco devices will not have the show version command,
or will give different output.
The following example identifies a Cisco product running Cisco IOS release
12.0(3) with an installed image name of C2500-IS-L:
Cisco Internetwork Operating System Software IOS (TM)
2500 Software (C2500-IS-L), Version 12.0(3), RELEASE SOFTWARE
The release train label is "12.0." The next example shows a product
running Cisco IOS release 12.0(2a)T1 with an image name of C2600-JS-MZ:
Cisco Internetwork Operating System Software IOS (tm)
C2600 Software (C2600-JS-MZ), Version 12.0(2a)T1, RELEASE SOFTWARE (fc1)
Additional information about Cisco IOS release naming can be found at
<http://www.cisco.com/warp/public/620/1.html>
http://www.cisco.com/warp/public/620/1.html.
Products Confirmed Not Vulnerable:
* Products that are not running Cisco IOS are not affected
* Products running Cisco IOS versions 12.0 and earlier (excluding 12.0
S), 12.1 mainline and 12.2 mainline are not vulnerable
* Products running IOS release trains that are not mentioned in the above
table are not vulnerable
* Products running any version of Cisco IOS that do not have OSPF
configured are not vulnerable
Details:
OSPF is a routing protocol defined by RFC 2328. It is designed to manage
IP routing inside an Autonomous System (AS). OSPF packets use IP protocol
number 89.
A vulnerability exists in the processing of an OSPF packet that can be
exploited to cause the reload of a system. Several parameters need to be
known by an attacker to successfully exploit this vulnerability. These are
the OSPF area number, netmask, hello, and dead timers that are configured
on the targeted interface.
Since OSPF needs to process Unicast packets as well as multicast packets,
this vulnerability can be exploited remotely. It is also possible for an
attacker to target multiple systems on the local segment at a time.
Using OSPF Authentication as described in the workarounds section can be
used to mitigate the effects of this vulnerability. Using OSPF
Authentication is a highly recommended security best practice
A Cisco device receiving a malformed OSPF packet will reset and may take
several minutes to become fully functional. This vulnerability may be
exploited repeatedly resulting in an extended DOS attack. This issue is
documented in bug ID CSCec16481.
Impact:
Successful exploitation of this vulnerability results in a reload of the
device. Repeated exploitation could result in a sustained DoS attack.
Software Versions and Fixes:
A table listing all the affected software version and their appropriate
fixes can be found at:
<http://www.cisco.com/warp/public/707/cisco-sa-20040818-ospf.shtml#software>
http://www.cisco.com/warp/public/707/cisco-sa-20040818-ospf.shtml#software
Obtaining Fixed Software:
Customers with Service Contracts
Customers with contracts should obtain upgraded software through their
regular update channels. For most customers, this means that upgrades
should be obtained through the Software Center on Cisco's worldwide
website at http://www.cisco.com.
Customers using Third-party Support Organizations
Customers whose Cisco products are provided or maintained through prior or
existing agreement with third-party support organizations such as Cisco
Partners, authorized resellers, or service providers should contact that
support organization for assistance with the upgrade, which should be free
of charge.
Customers without Service Contracts
Customers who purchase direct from Cisco but who do not hold a Cisco
service contract and customers who purchase through third-party vendors
but are unsuccessful at obtaining fixed software through their point of
sale should get their upgrades by contacting the Cisco Technical
Assistance Center (TAC). TAC contacts are as follows.
* +1 800 553 2447 (toll free from within North America)
* +1 408 526 7209 (toll call from anywhere in the world)
* e-mail: tac@cisco.com
Please have your product serial number available and give the URL of this
notice as evidence of your entitlement to a free upgrade. Free upgrades
for non-contract customers must be requested through the TAC.
Please do not contact either "psirt@cisco.com" or
"security-alert@cisco.com" for software upgrades.
Workarounds
The effectiveness of any workaround is dependent on specific customer
situations such as product mix, network topology, traffic behavior, and
organizational mission. Due to the variety of affected products and
releases, customers should consult with their service provider or support
organization to ensure any applied workaround is the most appropriate for
use in the intended network before it is deployed.
There are multiple workarounds available to mitigate the effects of this
vulnerability.
Using OSPF Authentication
OSPF authentication may be used as a workaround. OSPF packets without a
valid key will not be processed. MD5 authentication is highly recommended,
due to inherent weaknesses in plain text authentication. With plain text
authentication, the authentication key will be sent unencrypted over the
network, which can allow an attacker on a local network segment to capture
the key by sniffing packets.
Refer to <http://www.cisco.com/warp/public/104/25.shtml>
http://www.cisco.com/warp/public/104/25.shtml for more information about
OSPF authentication.
Infrastructure Access Control Lists
Although it is often difficult to block traffic transiting your network,
it is possible to identify traffic which should never be allowed to target
your infrastructure devices and block that traffic at the border of your
network. Infrastructure ACLs are considered a network security best
practice and should be considered as a long-term addition to good network
security as well as a workaround for this specific vulnerability. The
white paper "Protecting Your Core: Infrastructure Protection Access
Control Lists" presents guidelines and recommended deployment techniques
for infrastructure protection ACLs:
<http://www.cisco.com/warp/public/707/iacl.html>
http://www.cisco.com/warp/public/707/iacl.html.
ADDITIONAL INFORMATION
The information has been provided by <mailto:psirt@cisco.com> Cisco
Products Security.
The original article can be found at:
<http://www.cisco.com/warp/public/707/cisco-sa-20040818-ospf.shtml>
http://www.cisco.com/warp/public/707/cisco-sa-20040818-ospf.shtml
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