-----BEGIN PGP SIGNED MESSAGE----- We've had a report of nmap UDP scans crashing Cisco routers running Cisco IOS software version 12.0. This was apparently mentioned on BUGTRAQ, although the BUGTRAQ message has not yet arrived at Cisco. We've verifed that the problem does exist. We believe that it affects all Cisco routers running any variant of 12.0 (including 12.0T, 12.0S, etc.). We do *not* think that it affects any non-12.0 version. However, we got the bug report only three hours ago, have not yet finished characterizing it, and can't yet be completely sure which versions or which platforms are affected. This is very easy to exploit, and has now been announced very widely. Administrators should be on the lookout for it. The problem appears to be caused by packets sent to the router's syslog port (UDP port 514). A tested workaround is to use an access list to block incoming syslog traffic. You'd do this with something like this: access-list 101 deny udp any host <router-addr-1> eq 514 access-list 101 deny udp any host <router-addr-2> eq 514 access-list 101 deny udp any host <router-addr-3> eq 514 ... etc ... access-list 101 permit ip any any interface <interface-1> ip access-group 101 in interface <interface-2> ip access-group 101 in ... etc ... The access list needs to block syslog traffic destined for any of the router's own IP addresses. It should be applied on all interfaces running IP, including virtual interfaces and subinterfaces (but not loopback interfaces). This workaround *does* have a performance impact that may be significant for some users. The impact isn't usually extreme, but it may make a difference on a router that's already heavily loaded. Install it with care if you install it. This bug may cause different router platforms to crash differently. Some routers have been observed to reboot and claim that they were "restarted by power-on"; you won't necessarily get a stack trace from one of these crashes. Since this is only partially characterized, you may choose to hold the workaround in reserve and apply it only if you believe you are being attacked. We should have a formal notice with full details within the next few days. We cannot yet make any estimate of when a fix will be available; we should have more information by the time the formal notice comes out. If you find that you are actually attacked with this, please report the attack to Cisco at "security-alertat_private". For more information on Cisco security procedures, see http://www.cisco.com/warp/customer/791/sec_incident_response.shtml -- J. Bashinski Cisco Systems -----BEGIN PGP SIGNATURE----- Version: 2.6.3in Charset: noconv iQEVAwUBNn/CR0Zi51ggEbh5AQGqxwf8D/GrXbiUe9u6zNv2DpZqitZ1vJ2NaRIr QNKCHl5hz45udrHK/kQNIBw9i6SbqmXXZXhWpzUsRp8EBmNPIRvm8Yd1ZrtxLDHj pynfzcT+LOfS0dedfrscnTdf31RMIhxaxI79s0aMOeUpBoV+BAYr3i0eTVx+moim 711aM0AbBitielGryVOtp08vET60db/0NNhRKXMwSxnH8qojSFtTEO/rhm5jonWp fzmbJMkJSuSK0Gp3OJyInMeG0xtZwOL3GSWoz0WOLNqYHIizIdkWj4sxGnB9g8Q8 YJ7repLd+xRzISk1UNOdfgPRLR72zxQPgpCayHFyg/zWGN24bz3AFA== =1TXj -----END PGP SIGNATURE-----
This archive was generated by hypermail 2b30 : Fri Apr 13 2001 - 14:25:40 PDT