Cisco Security Advisory
Cisco IOS ARP Table Overwrite Vulnerability
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It is possible to send an Address Resolution Protocol (ARP) packet on a local broadcast interface (for example, Ethernet, cable, Token Ring, FDDI) which could cause a router or switch running specific versions of Cisco IOS® Software Release to stop sending and receiving ARP packets on the local router interface. This will in a short time cause the router and local hosts to be unable to send packets to each other. ARP packets received by the router for the router's own interface address but a different Media Access Control (MAC) address will overwrite the router's MAC address in the ARP table with the one from the received ARP packet. This was demonstrated to attendees of the Black Hat conference and should be considered to be public knowledge. This attack is only successful against devices on the segment local to the attacker or attacking host.
This vulnerability is documented in Cisco Bug ID CSCdu81936, and a workaround is available.
The complete notice will be available at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20011115-ios-arp-overwrite.
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This section provides details on affected products.
Vulnerable Products
The following products are affected if they run a software release that has the defect.
To determine if a Cisco product is running an affected IOS, log in to the device and issue the command show version. Cisco IOS software will identify itself as "Internetwork Operating System Software" or "IOS (tm)" software and will display a version number. Other Cisco devices either will not have the command show version, or will give different output. Compare the version number obtained from the router with the versions presented in the Software Versions and Fixes section below.
Cisco devices that may be running with affected IOS software releases include:
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Cisco routers in the AGS/MGS/CGS/AGS+, IGS, RSM, 800, ubr900, 1000,
1400, 1500, 1600, 1700, 2500, 2600, 3000, 3600, 3800, 4000, 4500, 4700, AS5200,
AS5300, AS5800, 6400, 7000, 7200, ubr7200, 7500, and 12000 series
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Most recent versions of the LS1010 ATM switch
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Catalyst 2900XL and 3500XL LAN switches
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Catalyst 2950 LAN switch
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Catalyst 3550 switch
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Catalyst 2948G-L3 & 4908G-L3
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Catalyst 4000 Layer 3 services module (WS-X4232-L3)
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Catalyst 5000 RSM/RSFC
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Catalyst 6000 MSFC
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Catalyst 6000 running native IOS
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Catalyst 8500 MSR/CSR
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Cisco DistributedDirector
Products Confirmed Not Vulnerable
If you are not running Cisco IOS software, you are not affected by this vulnerability.
Cisco products that do not run Cisco IOS software and are not affected by this defect include, but are not limited to:
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700 series dialup routers (750, 760, and 770 series) are not
affected.
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WAN switching products in the IGX and BPX lines are not affected.
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The MGX (formerly known as the AXIS shelf) is not affected.
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No host-based software is affected.
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The Cisco PIX Firewall is not affected.
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The Cisco LocalDirector is not affected.
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The Cisco Cache Engine is not affected.
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The Catalyst 2901/2902, 2948G, 2980G, 4000, 5000, and 6000 switches
running CatOS.
No other Cisco products are currently known to be affected by these vulnerabilities.
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Cisco routers in the AGS/MGS/CGS/AGS+, IGS, RSM, 800, ubr900, 1000,
1400, 1500, 1600, 1700, 2500, 2600, 3000, 3600, 3800, 4000, 4500, 4700, AS5200,
AS5300, AS5800, 6400, 7000, 7200, ubr7200, 7500, and 12000 series
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ARP packets, both request and reply, received by the router for the router's own interface address or global Network Address Translation (NAT) entries, but with a different MAC address, will overwrite the router's MAC address in the router's ARP table with the one in the ARP request or reply. Cisco IOS router devices will defend the MAC address of an interface for several attempts, but in an attempt to prevent an ARP storm, the device will accept the incorrect information into the ARP table, which causes the interface to stop accepting new ARP entries, and entries will not be accepted or updated in the ARP table. This behavior has been repaired to properly defend the interface MAC address, with rate limiting the response to avoid an ARP storm on the local network. This attack can only be carried out from the local network. This defect also impacts HSRP virtual interfaces. This defect is documented in Cisco Bug ID CSCdu81936 and is repaired in future versions of Cisco IOS code. This defect is duplicated by the following Cisco Bug ID's: CSCdv83509, CSCdv63206, CSCdv77242, CSCdv77220, CSCdu85209. Additionally, a configuration workaround is available.
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The workaround for this vulnerability is to enter the router interface MAC address into the arp table with a configuration entry, sometimes known as "hard coding" the ARP table entry.
The syntax for this command for routers and switches running IOS is as follows:
arp
The caveat to this workaround is identified with defect CSCdv04366, which will clear all manually entered MAC addresses from the ARP table, when they are the same as the interface MAC address, when the command "clear arp" is issued on the router. This workaround does not survive a reboot of the router, and must be re-written to the configuration after any reload or reboot.
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Each row of the table describes a release train and the platforms or products for which it is intended. If a given release train is vulnerable, then the earliest possible releases that contain the fix and the anticipated date of availability for each are listed in the Rebuild, Interim, and Maintenance columns. A device running any release in the given train that is earlier than the release in a specific column (less than the earliest fixed release) is known to be vulnerable, and it should be upgraded at least to the indicated release or a later version (greater than the earliest fixed release label).
When selecting a release, keep in mind the following definitions:
Maintenance
Most heavily tested and highly recommended release of any label in a given row of the table.
Rebuild
Constructed from the previous maintenance or major release in the same train, it contains the fix for a specific defect. Although it receives less testing, it contains only the minimal changes necessary to effect the repair.
Interim
Built at regular intervals between maintenance releases and receives less testing. Interims should be selected only if there is no other suitable release that addresses the vulnerability, and interim images should be upgraded to the next available maintenance release as soon as possible. Interim releases are not available via manufacturing, and usually they are not available for customer download from CCO without prior arrangement with the Cisco Technical Assistance Center (TAC).
In all cases, customers should exercise caution to be certain the devices to be upgraded contain sufficient memory and that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, contact the Cisco TAC for assistance, as shown in the following section.
More information on Cisco IOS software release names and abbreviations is available at http://www.cisco.com/warp/public/620/1.html.
Major Release
Description or Platform
Availability of Repaired Releases*
Affected Earlier Releases
Rebuild
Interim**
Maintenance
11.1 and earlier, all variants
Numerous
Upgrade to repaired release or use workaround
11.2-based Releases
Rebuild
Interim**
Maintenance
11.2
Major release for all platforms
Not affected after 11.2(13)
11.2P
New platform support
Not affected after 11.2(12)P
11.3-based Releases
Rebuild
Interim**
Maintenance
11.3
Major release for all platforms
Not affected after 11.3(3)
11.3T
Early deployment major release, feature-rich for early adopters
Not affected after 11.3(3)
12.0-based Releases
Rebuild
Interim**
Maintenance
12.0
General Deployment (GD) candidate: all platforms
12.0(19.6)
12.0DA
xDSL support: 6100, 6200
Unavailable
Upgrade recommended to 12.2DA
12.0DB
Early deployment release for 6400 NSP
Unavailable
Upgrade recommended to 12.1T or later
12.0DC
Early deployment release for 6400 NRP
Unavailable
Upgrade recommended to 12.2(2)B when available
12.0S
Core/ISP support: GSR, RSP, c7200
12.0(21)S 2002-Jan-14
12.0SC
Cable/broadband ISP: ubr7200
Unavailable
Upgrade recommended to 12.1EC, or use workaround
12.0SL
10000 ESR: c10k
Unavailable
Upgrade recommended to 12.0ST, or use workaround
12.0SP
c10720
12.0(20)SP
To Be Announced
12.0ST
MPLS/Tag Switching, GSR 12000, 7200, 7500
12.0(20)ST 2001-Nov-26
12.0T
Early Deployment(ED): VPN, Distributed Director, various platforms
Unavailable
Upgrade recommended to 12.1(11)
12.0W5
Catalyst switches: cat8510c, cat8540c, ls1010, cat8510m, cat8540m, cat5atm
12.0(20)W5(24)
2002-Jan-07
Catalyst switches: cat2948g-L3, cat4232
12.0(18)W5(22a)
2001-Dec-1
Catalyst switches: c6msm
12.0(16)W5(21b)
2001-Nov-29
12.0WC
Catalyst 2900xl
12.0(5)WC3 2002-Jan
12.0WT
Catalyst switches: cat4840g
Not affected
12.0XA
Early Deployment (ED): limited platforms
Unavailable
Upgrade recommended to 12.1(11)
12.0XB
Short-lived early deployment release
Unavailable
Upgrade recommended to 12.1(11)
12.0XC
Early Deployment (ED): limited platforms
Unavailable
Upgrade recommended to 12.1(11)
12.0XD
Early Deployment (ED): limited platforms
Unavailable
Upgrade recommended to 12.1(11)
12.0XE
Early Deployment (ED): limited platforms
Unavailable
Upgrade recommended to 12.1(11)E, available 2001-Dec-10
12.0XF
Early Deployment (ED): limited platforms
Unavailable
Upgrade recommended to 12.1(11)
12.0XG
Early Deployment (ED): limited platforms
Unavailable
Upgrade recommended to 12.1(11)
12.0XH
Early Deployment (ED): limited platforms
Unavailable
Upgrade recommended to 12.1(11)
12.0XI
Early Deployment (ED): limited platforms
Unavailable
Upgrade recommended to 12.1(11)
12.0XJ
Early Deployment (ED): limited platforms
Unavailable
Upgrade recommended to 12.1(11)
12.0XK
Early Deployment (ED): limited platforms
Unavailable
Upgrade recommended to 12.1(11)
12.0XL
Early Deployment (ED): limited platforms
Unavailable
Upgrade recommended to 12.1(11)
12.0XM
Short-lived early deployment release
Unavailable
Upgrade recommended to 12.1(11)
12.0XN
Early Deployment (ED): limited platforms
Unavailable
Upgrade recommended to 12.1(11)
12.0XP
Early Deployment (ED): limited platforms
Unavailable
Workaround recommended
12.0XQ
Short-lived early deployment release
Unavailable
Upgrade recommended to 12.1(11)
12.0XR
Short-lived early deployment release
Unavailable
Upgrade recommended to 12.1(11)
12.0XS
Short-lived early deployment release
Unavailable
Upgrade recommended to 12.1(11)E, available 2001-DEC-10
12.0XU
Early Deployment (ED): limited platforms
Unavailable
Upgrade recommended or use workaround
12.0XV
Short-lived early deployment release
Unavailable
Upgrade recommended to 12.2
12.1-based Releases
Rebuild
Interim**
Maintenance
12.1
General Deployment (GD) candidate: all platforms
12.1(10.3)
12.1(11)
12.1AA
Dial Support
12.1(10)AA 2001-Nov-12
12.1DA
xDSL Support: 6100, 6200
Unavailable
Upgrade recommended to 12.2.T
12.1DB
Cisco 6400 Universal Access Concentrator
Upgrade recommended to 12.2(2)B when available
12.1DC
xDSL NRP support: c6400r
Upgrade recommended to 12.2(2)B when available
12.1E
Core/ISP Support: GSR, RSP, c7200
12.1(11)E 2001-DEC-10
Catalyst 6000
12.1(08a)E05
12.1EA
Catalyst 2950
12.1(6)EA2 2001-Dec
Catalyst 3550
12.1(6)EA1a 2001-DEC
12.1EC
Early Deployment (ED): ubr7200, UBR Headend platforms
12.1(8.5)EC
12.1(9)EC
12.1EX
Catalyst 6000
Unavailable
Upgrade recommended to 12.1(11)E
12.1EY
Catalyst 8510, 8540, LS1010
Not Affected
12.1EZ
Early Deployment (ED): limited platforms
12.1(6)EZ4 2001-Nov-02
12.1T
New technology Early Deployment (ED): all platforms
Unavailable
Upgrade recommended to 12.2
12.1XA
Early Deployment (ED): limited platforms
Unavailable
Upgrade recommended to 12.2
12.1XB
Early Deployment (ED): limited platforms
Unavailable
Upgrade recommended to 12.2
12.1XC
Early Deployment (ED): limited platforms
Unavailable
Upgrade recommended to 12.2
12.1XD
Early Deployment (ED): limited platforms
Unavailable
Upgrade recommended to 12.2
12.1XE
Early Deployment (ED): limited platforms
Unavailable
Upgrade recommended to 12.2
12.1XF
Early Deployment (ED): limited platforms
12.1(2)XF5 2002-Jan
12.1XG
Early Deployment (ED): limited platforms
12.1(3)XG6 2002-Jan
12.1XH
Early Deployment (ED): limited platforms
Unavailable
Upgrade recommended to 12.2
12.1XI
Early Deployment (ED): limited platforms
Unavailable
Upgrade recommended to 12.2
12.1XJ
Early Deployment (ED): limited platforms
Unavailable
Upgrade recommended to 12.2
12.1XK
Early Deployment (ED): limited platforms
Unavailable
Upgrade recommended to 12.2
12.1XL
Early Deployment (ED): limited platforms
Unavailable
Upgrade recommended to 12.2
12.1XM
Early Deployment (ED): limited platforms
12.1(5)XM6 2001-Dec-03
12.1XP
Early Deployment (ED): limited platforms
Unavailable
Upgrade recommended to 12.2(2)T
12.1XQ
Early Deployment (ED): limited platforms
Unavailable
Upgrade recommended to 12.2(2)T
12.1XR
Early Deployment (ED): limited platforms
Unavailable
Upgrade recommended to 12.2(7)T
12.1XS
Early Deployment (ED): limited platforms
12.2(2)XC1 2001-DEC-3
12.1XT
Early Deployment (ED): limited platforms
Unavailable
Upgrade recommended to 12.2(7)T
12.1XU
Early Deployment (ED): limited platforms
Not affected
12.1XV
Early Deployment (ED): limited platforms
12.2(2)XB2 2001-DEC-17
12.2(2)XB2 2001-DEC-17
12.1XW
Early Deployment (ED): limited platforms
12.1(11)
12.1XX
Early Deployment (ED): limited platforms
12.1(11)
12.1YA
Early Deployment (ED): limited platforms
12.2(2)XB
12.1YB
Early Deployment (ED): limited platforms
12.1(5)YB5 2002-Jan
12.1YC
Early Deployment (ED): limited platforms
12.1(5)YC2 2002-Jan
12.1YD
Early Deployment (ED): limited platforms
Migrate to 12.2(7)T
12.1YE
Early Deployment (ED): limited platforms
12.1(5)YE4 2001-Nov-19
12.1YF
Early Deployment (ED): limited platforms
12.1(5)YF3 2001-Nov
12.1YH
Early Deployment (ED): limited platforms
Not Affected
Affected 12.2-based Releases
Rebuild
Interim**
Maintenance
12.2
General Deployment (GD) candidate: all platforms
12.2(4.2)
12.2(5)
12.2DD
7200, 7400
12.2(2)DD1 2001-Nov-19
12.2T
Early Deployment (ED): limited platforms
12.2(7)T 2002-Feb
12.2XA
Early Deployment (ED): limited platforms
12.2(2)XA4 2001-Dec-3
12.2XB
Early Deployment (ED): limited platforms
12.2(2)XB2 2001-Dec-17
12.2XC
Early Deployment (ED): limited platforms
12.2(2)XC1 2001-DEC-3
12.2XD
Early Deployment (ED): limited platforms
12.2(1)XD3 2002-Jan
12.2XE
Early Deployment (ED): limited platforms
12.2(1)XE2 2002-Jan
12.2XG
Early Deployment (ED): limited platforms
12.2(2)XG1 2001-DEC-17
12.2XH
Early Deployment (ED): limited platforms
12.2(2)XH2 2002-Jan
12.2XI
Early Deployment (ED): limited platforms
12.2XJ
Early Deployment (ED): limited platforms
12.2(2)XJ2 2002-Jan
12.2XK
Early Deployment (ED): limited platforms
12.2(2)XK5 2002-Jan
12.2XQ
Early Deployment (ED): limited platforms
12.2(2)XQ2 2002-Jan
Notes
* All dates are estimated and subject to change.
** Interim releases are subjected to less rigorous testing than regular maintenance releases, and may have serious bugs.
*** This release does not have a rebuild solution. Customers should upgrade to 12.2T when it becomes available. This is not a misprint.
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This vulnerability was disclosed at the Black Hat conferences in Las Vegas this year by Kevin DePeugh
and Jeff Nathan . There have been isolated reports of exploitation of this vulnerability, and workarounds implemented circumvented the attacks. This attack is known as the "Sonic Boom," and tools are readily available.
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To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco.
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Revision 1.3
2002-July-22
Updates to Software Versions and Fixes section.
Revision 1.2
2001-December-18
Updates to Summary, Affected Products, Impact, Software Versions and Fixes, and Workaround sections.
Revision 1.1
2001-November-21
Release table updates
Revision 1.0
2001-November-15
For public release 15-NOV-2001 08:00 AM US/Pacific (UTC-0700)
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