Document ID: 59860
For Public Release 2002 May 21
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Original Report: http://www.phenoelit.de/stuff/CiscoICMP.txt. Cisco responded with the following, which is also archived at http://www.securityfocus.com/archive/1/273488 .
To: BugTraq Subject: Cisco IOS ICMP redirect DoS - Cisco's response Date: May 21 2002 5:45PM Author: Damir Rajnovic <gaus cisco com> Message-ID: <email@example.com> -----BEGIN PGP SIGNED MESSAGE----- Hello, We can confirm the finding made by FX phenoelit de This issue is assigned Cisco bug ID CSCdx32056. The fix has been developed and it is being committed into all affected releases. The situation in Cisco IOS 12.x code is that the redirect cache will only grow if "ip routing" is disabled. The Cisco IOS 11.x code will populate the redirect cache ignoring the state of the "ip routing". The redirect cache is fixed in size and an entry timeout is four hours. By filling the redirect cache the memory is consumed. If the device is already low on memory that may cause further irregularities in the device's performance. Effects can vary, some of them can be: new routes can not be learned, new MAC entries might not be added, Telnet session might not be established, new CDP entries might not be added. Depending on the exact configuration and circumstances, the device may become totally unresponsive. The device should recover by itself after the four hours when the entries will start to timeout. The workaround for users running Cisco IOS 11.x code is to block all ICMP redirect messages that are sent to the router itself. That can be accomplished this way: router(config)#access-list 101 deny icmp any host <device_IP> redirect .... (the rest of the access-list 101) router(config)#interface eth0 router(config-if)#ip access-group 101 in This example will block all ICMP packets, sent to the router itself, coming from the eth0 interface. All transit ICMP redirect packets will be allowed through. Although, Cisco IOS 12.x code is less exposed we recommend to block all ICMP redirect packets sent to the device itself. Gaus -----BEGIN PGP SIGNATURE----- Version: PGP 6.5.3 iQEVAwUBPOqHtw/VLJ+budTTAQFsvwf/bsR/O6QMhPjxr8sGtQJ58Xr/EC1WkiQn H0jIPGsma9wv5F4hWlpjRiZfVX9GfEoLs8yrknBWXQ08cwB+TizzsSdUVnQXkp4z 6gYzHymdSbvZW/pSJyPa4J0r80MoVN8qOgavD6iCbvlT8GA67lS13YdLHDYos2cP 3c8B8UwXGiOdCJQAI1UY2gg592owahSjXRaTwStitGiwmRuhKDQE0sqWDN1h0YPw B85QJYpds2HrsC31tYO3P0rocToZFvUPA4zd5MaaqZ4gbdlTZDU5p0ktDbnRJZy/ KAfm/YV9yQIFjJzUzmcy7iZj+09pr/qNocvAvTw24CGcxGPXX+wDow== =y3UB -----END PGP SIGNATURE----- ============== Damir Rajnovic <psirt cisco com>, 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 is no insolvable problems. The question is can you accept the solution?
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|Updated: May 21, 2002||Document ID: 59860|