Date: Mon, 15 Jul 2002 10:26:41 -0700 From: Lars Eggert <larse@ISI.EDU> To: net@freebsd.org, Joe Touch <touch@ISI.EDU>, Yu-Shun Wang <yushunwa@ISI.EDU> Subject: Denial-of-service through ARP snooping Message-ID: <3D3305D1.5050103@isi.edu>
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This is a cryptographically signed message in MIME format. --------------ms010907040904060507060705 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Hi, we've just stumbled over an interesting denial-of-service case at IETF. I was playing with a custom startup script to auto-configure local interfaces, part of which sent out an ARP request "borrowing" the IP address of the gateway as source address (e.g. "who-has X tell X"). It seems that most/all BSDs do ARP snooping, and will happily add the apparent "new" MAC address of the gateway to their ARP table, possibly flushing the existing one of the default gateway. This of course causes everybody's packets to fall on the floor until the fake ARP entry times out. (RFC826 seems to imply that snooping is allowed, the "packet reception" section doesn't seem to limit *how* packets are received.) Maybe ARP entries should only be updated when replies are received in response to locally originated requests? Initial latency might be a bit higher, since the ARP table won't be pre-loaded, but it will add some protection against this particular DOS attack. Lars -- Lars Eggert <larse@isi.edu> USC Information Sciences Institute --------------ms010907040904060507060705 Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="smime.p7s" Content-Description: S/MIME Cryptographic Signature MIAGCSqGSIb3DQEHAqCAMIACAQExCzAJBgUrDgMCGgUAMIAGCSqGSIb3DQEHAQAAoIIIrjCC ArUwggIeoAMCAQICAwWBRzANBgkqhkiG9w0BAQIFADCBkjELMAkGA1UEBhMCWkExFTATBgNV BAgTDFdlc3Rlcm4gQ2FwZTESMBAGA1UEBxMJQ2FwZSBUb3duMQ8wDQYDVQQKEwZUaGF3dGUx HTAbBgNVBAsTFENlcnRpZmljYXRlIFNlcnZpY2VzMSgwJgYDVQQDEx9QZXJzb25hbCBGcmVl bWFpbCBSU0EgMjAwMC44LjMwMB4XDTAxMDgyNDE2NDAwMFoXDTAyMDgyNDE2NDAwMFowVDEP MA0GA1UEBBMGRWdnZXJ0MQ0wCwYDVQQqEwRMYXJzMRQwEgYDVQQDEwtMYXJzIEVnZ2VydDEc MBoGCSqGSIb3DQEJARYNbGFyc2VAaXNpLmVkdTCBnzANBgkqhkiG9w0BAQEFAAOBjQAwgYkC gYEA0AvLBsD78nxcUHeHkaMgl3b4qYPnfgbf8Lh+HQP8RgGMRG/Yb+vTpkGezlwt9pkJxiD1 1uZDy4CNNJUu3gKxKSb+zRV70O+lkwwftuHoLHoH4xwo3LcQ2LGDpd+I95tUN4dfJ3TmeEcU SF50dC/SuUI4w8AlhXQ8IxrhgdayTpECAwEAAaNWMFQwKgYFK2UBBAEEITAfAgEAMBowGAIB BAQTTDJ1TXlmZkJOVWJOSkpjZFoyczAYBgNVHREEETAPgQ1sYXJzZUBpc2kuZWR1MAwGA1Ud EwEB/wQCMAAwDQYJKoZIhvcNAQECBQADgYEAheZhn0pQA8zI7U2K1ZIAl11j0a1DKxnp3GtT vOUrGRB3WvYxidvdZ1kizhEsWeXU81TkNDH0DaRqtOEeu6Q2OhB+jeKEqY7IDAJE4/fI0e+d 6PnG1hd+vEvYmsKHkmzBhPc94XUOKNWO+qVNP2NGyNI3QIDy5wX4fdcOo1S34r4wggK1MIIC HqADAgECAgMFgUcwDQYJKoZIhvcNAQECBQAwgZIxCzAJBgNVBAYTAlpBMRUwEwYDVQQIEwxX ZXN0ZXJuIENhcGUxEjAQBgNVBAcTCUNhcGUgVG93bjEPMA0GA1UEChMGVGhhd3RlMR0wGwYD VQQLExRDZXJ0aWZpY2F0ZSBTZXJ2aWNlczEoMCYGA1UEAxMfUGVyc29uYWwgRnJlZW1haWwg UlNBIDIwMDAuOC4zMDAeFw0wMTA4MjQxNjQwMDBaFw0wMjA4MjQxNjQwMDBaMFQxDzANBgNV BAQTBkVnZ2VydDENMAsGA1UEKhMETGFyczEUMBIGA1UEAxMLTGFycyBFZ2dlcnQxHDAaBgkq hkiG9w0BCQEWDWxhcnNlQGlzaS5lZHUwgZ8wDQYJKoZIhvcNAQEBBQADgY0AMIGJAoGBANAL ywbA+/J8XFB3h5GjIJd2+KmD534G3/C4fh0D/EYBjERv2G/r06ZBns5cLfaZCcYg9dbmQ8uA jTSVLt4CsSkm/s0Ve9DvpZMMH7bh6Cx6B+McKNy3ENixg6XfiPebVDeHXyd05nhHFEhedHQv 0rlCOMPAJYV0PCMa4YHWsk6RAgMBAAGjVjBUMCoGBStlAQQBBCEwHwIBADAaMBgCAQQEE0wy dU15ZmZCTlViTkpKY2RaMnMwGAYDVR0RBBEwD4ENbGFyc2VAaXNpLmVkdTAMBgNVHRMBAf8E AjAAMA0GCSqGSIb3DQEBAgUAA4GBAIXmYZ9KUAPMyO1NitWSAJddY9GtQysZ6dxrU7zlKxkQ d1r2MYnb3WdZIs4RLFnl1PNU5DQx9A2karThHrukNjoQfo3ihKmOyAwCROP3yNHvnej5xtYX frxL2JrCh5JswYT3PeF1DijVjvqlTT9jRsjSN0CA8ucF+H3XDqNUt+K+MIIDODCCAqGgAwIB AgIQZkVyt8x09c9jdkWE0C6RATANBgkqhkiG9w0BAQQFADCB0TELMAkGA1UEBhMCWkExFTAT BgNVBAgTDFdlc3Rlcm4gQ2FwZTESMBAGA1UEBxMJQ2FwZSBUb3duMRowGAYDVQQKExFUaGF3 dGUgQ29uc3VsdGluZzEoMCYGA1UECxMfQ2VydGlmaWNhdGlvbiBTZXJ2aWNlcyBEaXZpc2lv bjEkMCIGA1UEAxMbVGhhd3RlIFBlcnNvbmFsIEZyZWVtYWlsIENBMSswKQYJKoZIhvcNAQkB FhxwZXJzb25hbC1mcmVlbWFpbEB0aGF3dGUuY29tMB4XDTAwMDgzMDAwMDAwMFoXDTA0MDgy NzIzNTk1OVowgZIxCzAJBgNVBAYTAlpBMRUwEwYDVQQIEwxXZXN0ZXJuIENhcGUxEjAQBgNV BAcTCUNhcGUgVG93bjEPMA0GA1UEChMGVGhhd3RlMR0wGwYDVQQLExRDZXJ0aWZpY2F0ZSBT ZXJ2aWNlczEoMCYGA1UEAxMfUGVyc29uYWwgRnJlZW1haWwgUlNBIDIwMDAuOC4zMDCBnzAN BgkqhkiG9w0BAQEFAAOBjQAwgYkCgYEA3jMypmPHCSVFPtJueCdngcXaiBmClw7jRCmKYzUq bXA8+tyu9+50bzC8M5B/+TRxoKNtmPHDT6Jl2w36S/HW3WGl+YXNVZo1Gp2Sdagnrthy+boC 9tewkd4c6avgGAOofENCUFGHgzzwObSbVIoTh/+zm51JZgAtCYnslGvpoWkCAwEAAaNOMEww KQYDVR0RBCIwIKQeMBwxGjAYBgNVBAMTEVByaXZhdGVMYWJlbDEtMjk3MBIGA1UdEwEB/wQI MAYBAf8CAQAwCwYDVR0PBAQDAgEGMA0GCSqGSIb3DQEBBAUAA4GBADGxS0dd+QFx5fVTbF15 1j2YwCYTYoEipxL4IpXoG0m3J3sEObr85vIk65H6vewNKjj3UFWobPcNrUwbvAP0teuiR59s ogxYjTFCCRFssBpp0SsSskBdavl50OouJd2K5PzbDR+dAvNa28o89kTqJmmHf0iezqWf54TY yWJirQXGMYICpjCCAqICAQEwgZowgZIxCzAJBgNVBAYTAlpBMRUwEwYDVQQIEwxXZXN0ZXJu IENhcGUxEjAQBgNVBAcTCUNhcGUgVG93bjEPMA0GA1UEChMGVGhhd3RlMR0wGwYDVQQLExRD ZXJ0aWZpY2F0ZSBTZXJ2aWNlczEoMCYGA1UEAxMfUGVyc29uYWwgRnJlZW1haWwgUlNBIDIw MDAuOC4zMAIDBYFHMAkGBSsOAwIaBQCgggFhMBgGCSqGSIb3DQEJAzELBgkqhkiG9w0BBwEw HAYJKoZIhvcNAQkFMQ8XDTAyMDcxNTE3MjY0MlowIwYJKoZIhvcNAQkEMRYEFOl+SHloSKx1 lzShQJiyKeRQlesYMFIGCSqGSIb3DQEJDzFFMEMwCgYIKoZIhvcNAwcwDgYIKoZIhvcNAwIC AgCAMA0GCCqGSIb3DQMCAgFAMAcGBSsOAwIHMA0GCCqGSIb3DQMCAgEoMIGtBgsqhkiG9w0B CRACCzGBnaCBmjCBkjELMAkGA1UEBhMCWkExFTATBgNVBAgTDFdlc3Rlcm4gQ2FwZTESMBAG A1UEBxMJQ2FwZSBUb3duMQ8wDQYDVQQKEwZUaGF3dGUxHTAbBgNVBAsTFENlcnRpZmljYXRl IFNlcnZpY2VzMSgwJgYDVQQDEx9QZXJzb25hbCBGcmVlbWFpbCBSU0EgMjAwMC44LjMwAgMF gUcwDQYJKoZIhvcNAQEBBQAEgYB/KM70J7rJaGNXpUpLlo115D6EzZ3usMJ39zjbX239pug3 PanJYSbRnlvJjRuUpjLP1fl5S6O83vP1t5TXYLYVRtIt4RAEnpXEoDSbFa8HZ65s3VmXk6PK 725Mi6EkcBEXLa67TjHH6dkiGJwL2qVqT8OacTWeJ1ch6jJjE882pQAAAAAAAA== --------------ms010907040904060507060705-- To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message
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