Re: Cisco IOS vulnerability

From: Jeff Kell (jeff-kellat_private)
Date: Sat Jul 19 2003 - 20:56:29 PDT

  • Next message: Andrew Bates: "Re: Cisco 0-day? [Was: strange protocol scans (and MOBP plug)]"

    jlewisat_private wrote:
    
    > That's a different issue.  undefined access list = you referenced an 
    > access-list that does not exist.  In that case, it's as if you didn't 
    > reference the access-list.
    > 
    > I think this is a common pitfal for beginers with IOS.  You need to modify 
    > an access-list, so you telnet into the router, conf t, no access-list 
    > blah, then start typing in the new version of the access-list.  Hopefully, 
    > your first line is permit tcp any any est, because once you start 
    > reentering the access-list, there's the implicit deny all all at the 
    > end...so if you're getting to the router through the interface using the 
    > access-list you're modifying, you may block yourself out.
    > 
    > For that reason, it's generally best to create a new access-list, then 
    > modify the interface config to use that new access-list.
    
    Even better, show config to get the ACL, cut and paste it into an 
    editor.  Add "interface foo" and "no ip access-group this-acl in" and 
    "no ip access-list extended this-acl" at the beginning, and an 
    "interface foo" and "ip access-group this-acl in" at the end.  Then you 
    can cut-and-paste the config without any side effects (or you can store 
    it on a tftp server and config net from there).
    
    Jeff
    
    
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