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Field Notice - IOS Accepts ICMP Redirects in Non-default
Configuration Settings
Field Notice Number 23074
Publish Date 2003-February-10
Author Damir Rajnovic <gausat_private>
Products Affected
Product Comments
------------------------------------------------------------------
All Cisco IOS This issue is not specific to any Cisco IOS
software release or device configuration. The device is
only vulnerable if IP routing is disabled. The
IP routing is enabled by default and it must be
explicitly disabled if required.
Problem Description
If a router has IP routing disabled it will accept bogus ICMP
redirect packets and modify its routing table accordingly. With
IP routing disabled, the router will act as a Host and it will
comply with the Host Requirements given in the RFC1122. If IP
routing is enabled(which it is by default) ICMP redirect packets
are received and recognized but ignored. The router will not update
its routing table with the information present in the redirect
packets.
Background
This vulnerability was reported to Cisco by Ofir Arkin while at
@stake (currently The Sys-Security Group, ofir@sys-security.com).
Problem Symptoms
By sending bogus ICMP redirect packets a malicious user can either
disrupt or intercept communication from a router.
The disruption can be accomplished by advertising that a default
gateway is an unused IP address from the local subnet. That will
effectively prevent the router from sending any packets to any
destination that is outside the local subnet.
Another possibility is to advertise a gateway that is on the
completely different subnet. If there is a device that will proxy
ARP request for this bogus gateway, all victim's traffic destined
outside of the local subnet may be forwarded to the bogus gateway,
which would cause the victim's traffic to leak out of the local
subnet to a device of attacker's choosing. If there is no device
that will proxy ARP requests for a bogus gateway then the scenario
collapses to the first scenario where traffic is simply blocked.
The last possibility is that malicious user inserts a default
gateway whose IP address is the address of the attacker's machine
itself. That way a malicious user will be able to receive all
victim's traffic host that is destined outside of the local subnet.
That traffic can subsequently be recorded or manipulated at the
attackers' will. The traffic can even be forwarded to the correct
gateway so that the victim will be unable to notice what is going
on. That a malicious user could participate as a default gateway
and intercept and record legitimate traffic is normal operation,
and is based on availability principles, and is not dependent on
the vulnerability of accepting llegitimate ICMP messages.
Workaround/Solution
The workaround is to prevent the router from acting upon ICMP
redirect packets. This can be accomplished in the following manner:
Router(config)#no ip icmp redirect
The preferred way would be to upgrade to the fixed IOS release.
The first fixed releases are:
12.2(13.03)B
12.2(12.05)T
12.2(12.05)S
12.2(12.05)
12.2(12.02)S
12.2(12.02)T
These releases are fixed as of the time this notice was written.
For the most current list of the fixed releases consult the DDTS
CSCdx92043.
DDTS
DDTS Description
CSCdx92043 IOS accepts wrong ICMP redirects
For More Information
Registered users (http://www.cisco.com/register) can view the
DDTS details.
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Damir Rajnovic <psirtat_private>, PSIRT Incident Manager, Cisco Systems
<http://www.cisco.com/go/psirt> Telephone: +44 7715 546 033
200 Longwater Avenue, Green Park, Reading, Berkshire RG2 6GB, GB
==============
There are no insolvable problems.
The question is can you accept the solution?
This archive was generated by hypermail 2b30 : Tue Feb 11 2003 - 06:46:39 PST