RE: preventing XSS and SQL injection?

["Behm, Jeffrey L." <BehmJL () bvsg com>]

But adding all legitimate traffic patterns would seem to be a less
difficult task 
than trying to add all known (and unknown) bad patterns. You seem to
have hit 
the nail on Marcus' proverbial head with regards to the point he seems
to me to
be trying to make regarding "permit only what is good." 

On Thursday, June 02, 2005 1:58 PM, ArkanoiD spake:

> It is ok when securing server traffic, but becames extremely difficult
when it
> comes to client proxy, because there are too many legitimate traffic
patterns to add :-(
> On Thu, Jun 02, 2005 at 03:03:36PM -0400, Marcus J. Ranum wrote:
> > ArkanoiD wrote:
> > > Are there any hints on preventing cross-site scripting attacks and
> > > SQL injection on proxy firewall by, say, applying some regexps on
url data?
> > Instead of trying to block what is bad, permit only what is good.
> >
> > Can you observe your legitimate traffic and converge forward
> > > on a set of regexps that define what "good" looks like? Then
> > deny all else. You might be able to do that in a fairly
straightforward
> > manner using Squid proxy cache ACLs.
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