Re: Linux 2.4.27 SECURITY BUG - TCP Local and REMOTE(verified) Denial of Service Attack

Willy Tarreau
2004-09-14T19:45:27Z

Hi Alan,

On Tue, Sep 14, 2004 at 04:10:36PM +0100, Alan Cox wrote:
> On Maw, 2004-09-14 at 15:55, Paul Jakma wrote:
> > Hmm, yes, I hadnt thought of the attack-mitigating aspects of
> > graceful restart. Though, without other measures, the session is
> > still is open to abuse (send RST every second).
>
> Of course its much easier to just send "must fragment, size 68" icmp
> replies and guess them that way. This is spectacularly more effective
> and various vendors highly invalid rst acking crap won't save you.

Just wondering, I have not checked. Isn't the "must fragment" message
supposed to embed part of the packet it couldn't send in return ? If
this is the case (and if the victim processes it correctly), it would
need to guess a recent valid content. If it's not the case, I suspect
it would simply update the path mtu in the route cache, thus giving
spectacular effects :-)

Cheers,
Willy