ras, all, On Thu, Jun 23, 2005 at 12:14:12AM -0400, Richard A Steenbergen wrote:
On Wed, Jun 22, 2005 at 10:04:09PM -0400, Todd Underwood wrote:
a) many (all?) implementations of md5 protection of tcp expose new, easy-to-exploit vulnerabilities in host OSes. md5 verification is slow and done on a main processor of most routers. md5 verification typically takes places *before* the sequence number, ports, and ip are checked to see whether they apply to a valid session. as a result, you've exposed a trivial processor DOS to your box.
Well, I think they've finally fixed this one by now, at least everyone that I'm aware of has done so. Immediately following the whining to start deploying MD5 is was certainly the case that many implementations did stupid stuff like process MD5 before running other validity checks like sequence numbers which are far less computationally intensive, and there were a few MSS bugs that popped up, but they should have all been worked out by now. I don't think that anyone running modern code is suffering any more attack potential because of this.
my understanding is that md5 is still checked before the ttl-hack check takes place on cisco (and perhaps most router platforms). new attack vector for less security than you had before. oh well. ras: can you confirm that it is possible to implement ttl-hack and have it check *before* md5 signature checks? the chaos (and crappy quality of the implementations) during the panic demonstrates two other things: rolling out magic code because your vendor tells you to is a bad idea; slapping together a hack on top of a well-designed protocol without careful thought and testing is a terrible idea. t. -- _____________________________________________________________________ todd underwood director of operations & security renesys - interdomain intelligence todd@renesys.com www.renesys.com