Andrew, This is a sufficiently significant risk that should be documented in the security wiki. I encourage you to do so.
On Sat, Nov 14, 2009 at 7:21 PM, Andrew Arnott <[email protected]> wrote: > That's right, John. > For a vulnerable RP, an attacker could set up any URL to impersonate any > other user at the RP simply by logging into the RP with his own URL, after > configuring it to send back the Content-Location header with the victim's > claimed_id as its value. > I've confirmed that the extremeswankopenid library is vulnerable to this > attack, and have contacted the author already. > Regarding your question about how this is different than delegating your > identifier to a victim's OpenID... I'm not familiar with such an approach, > or how that would be exploited. > -- > Andrew Arnott > "I [may] not agree with what you have to say, but I'll defend to the death > your right to say it." - S. G. Tallentyre > > > On Sat, Nov 14, 2009 at 10:50 AM, John Bradley <[email protected]> wrote: >> >> This is a attack on discovery. >> If the RP performs discovery on URL A the owner of URL A can return a XRDS >> with a content-Location header for URL B. The RP now believes that whatever >> OP endpoint is in the XRDS is authoritative for URL B without having >> retrieved the actual XRDS for it, only the one for URL A claiming to be B. >> The problem is that .Net "helps" the application by making it think a >> redirect has taken place when it hasn't. >> There are lots of times when this works just fine however the claimed_id >> is tied to the product of the second normalization so is vulnerable to this >> sort of fake redirect. >> Andrew can provide more of the details. >> John B. >> On 2009-11-14, at 2:24 PM, Allen Tom wrote: >> >> Hi Andrew, >> >> Would an attacker be able to exploit this issue by returning the >> Content-Location HTTP response header for an URL that he owns, making his >> URL equivalent to a victim's OpenID? How is this different from having the >> attacker delegating his URL to the victim's OpenID? >> >> Can you outline a scenario where the Content-Location HTTP header is >> exploited? >> >> Thanks >> Allen >> >> >> >> Arnott wrote: >> >> Just a heads up from something I recently became aware of that impacted >> older versions of dotnetopenid. >> The HTTP protocol defines a Content-Location HTTP response header that >> allows the web server to suggest to the client that another URL would be >> equivalent to the one that client actually pulled from. It is not a >> redirect, but merely a suggestion that two URLs are equivalent. For the >> purposes of OpenID claimed identifier discovery, it is imperative that an >> OpenID RP ignore this header, lest a web server upon which discovery was >> performed can spoof an arbitrary claimed_id's identity by fooling the RP >> into thinking it discovered an identifier that in fact it did not. >> In particular, .NET's "helpful" HTTP stack automatically reads this header >> and reports it to the client as if it was in fact that actual URL that was >> pulled from even though it wasn't. Since .NET follows redirects >> automatically by default, a legitimate redirect and this Content-Location >> header are indiscernable, which is really bad. This is fixed in the >> dotnetopenid and dotnetopenauth libraries. >> Other RP library/site authors should verify that the HTTP stack they are >> using ignore this header, or workaround the issue. >> I've set up a test on test-id.org where an RP can very quickly assess >> whether they are vulnerable. Please take a moment to find out, and fix it >> ASAP if you are. >> http://test-id.org/RP/IgnoresContentLocationHeader.aspx >> -- >> Andrew Arnott >> "I [may] not agree with what you have to say, but I'll defend to the death >> your right to say it." - S. G. Tallentyre >> >> ________________________________ >> _______________________________________________ >> security mailing list >> [email protected] >> http://lists.openid.net/mailman/listinfo/openid-security >> >> >> _______________________________________________ >> security mailing list >> [email protected] >> http://lists.openid.net/mailman/listinfo/openid-security >> > > > _______________________________________________ > security mailing list > [email protected] > http://lists.openid.net/mailman/listinfo/openid-security > > -- --Breno +1 (650) 214-1007 desk +1 (408) 212-0135 (Grand Central) MTV-41-3 : 383-A PST (GMT-8) / PDT(GMT-7) _______________________________________________ security mailing list [email protected] http://lists.openid.net/mailman/listinfo/openid-security
