Hi, The exploits that you are talking about are inherent to the HTTP protocol. There's no way for us to get around them. We could use an http_reffer on the post but a good hack can spoof that to. Basically the only way you can be totally sure is by using dedicated sockets on SSL and that is what Payflow Pro does. In addition the Payflow Pro client has a cert folder in the SDK that validates that you are talking to VeriSign on the other end an not someone spoofing the address of the transaction servers. Payflow Link only allows Sale, Authorization, and Delay Capture transactions to be posted to it so effectively the only malicious thing you could do is tell someone that more sales have come through their shopping cart program than really have. Payflow Link merchants should use their carts to Authorize transactions then capture the transactions via the secure VeriSign Administrative site and they should also check their carts results against what appear in the VeriSign administrative site because VeriSign is the secure connection to the card issuing banks, not their shopping carts. Because of the HTTP protocol you might be able to intercept a transaction on a carts page and change the amounts etc before it gets to the VeriSign transaction broker where it secure but again this is an HTTP issue. You can't post credits via Payflow Link so you can't really exploit Payflow Link to commit fraud if that's what you ultimately want to get at. If someone sends extra confirmations back to a cart the customer can always contact the merchant and resolve the situation assuming the merchant uses the authorization followed by capture via the VeriSign Manager method. Thank You, Dan G. 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To get started, go to: <http://www.verisign.com/cgi-bin/go.cgi?a=w175248930810000> ************************************************************************ -----Original Message----- From: support Sent: Friday, January 04, 2002 10:21 PM To: vps-support Subject: Re : Fw: VERISIGN "PAYFLOW LINK" PAYMENT SERVICE SECURITY FAILURE (#5947-000093-7546\939465) (#5947-000093-7546\939465) ORIGINAL MESSAGE: ----------------- From: nbailey@hotmail.com Posted At: 15:56:01.530 01/04/2002 Posted To: support@verisign.com Subject: Fw: VERISIGN "PAYFLOW LINK" PAYMENT SERVICE SECURITY FAILURE Please investigate and forward to the appropriate Verisign employees... ----- Original Message ----- From: "keith royster" <keith@theroysters.com> To: <bugtraq@securityfocus.com> Sent: Friday, January 04, 2002 2:24 PM Subject: VERISIGN "PAYFLOW LINK" PAYMENT SERVICE SECURITY FAILURE > VERISIGN PAYFLOW PAYMENT SERVICE SECURITY FAILURE > > PAYFLOW LINK SERVICE DESCRIPTION: The final checkout page of various online > shopping cart applications presents the shopper with a form asking for credit > card acct#, exp date, etc. When the shopper submits the form, the data is sent > directly to the vendor's PayFlow Link account at Verisign for validation. If > the credit card information is validated, Verisign authorizes payment and > submits the data back to the vendors shopping cart application. When the > vendor's shopping app receives this data, it assumes payment was authorized and > finalizes the order for the vendor to fill and ship it. > > EXPLOIT #1: On the final checkout page, save the HTML to disk (keeping browser > open to maintain session) and edit the ACTION= portion of the form to direct > the data back at the shopping cart instead of to verisign. The exact URL > should match that which verisign would submit a validated order to. Save the > edited HTML, reload in your browser, and submit bogus credit card info with > your order. Since there is no authentication between Verisign and the shopping > application, the shopping app will think that the card was authorized, and so > it will finalize the order. > > EXPLOIT #2: Sign up for a free demo PayFlow Link account at Verisign. While in > demo mode, this account will "validate" almost any credit card info submitted > to it as long as the card# meets basic format, expiration date hasn't expired, > and amount <= $100. This demo account should be configured to send the > confirmation information to the exploitee's shopping system. Then perform a > similar HTML edit of the final checkout page as above, only this time change > the hidden form tag to direct the payment to the demo PayFlow Link account. > Save the HTML, reload in your browser, and submit bogus credit card info. > > THE RISK: Vendors that do no validate payment in their Verisign acct prior to > shipment, or those that offer immediate downloads of software upon payment, are > vulnerable to theft. > > THE FIX: In a communication from Verisign, they recommend upgrading to their > more secure PayFlow Pro product if you have security concerns with PayFlow Link. > > WHAT I KNOW: I have successfully performed both exploits on a Miva Merchant > 3.x shopping cart. Due to a lack of accessability, I have not tested other > shopping cart applications or other versions of Miva Merchant. I have > communicated this information to both Miva and Verisign. Verisign tested and > confirmed both exploits as well. They then responded that they will work with > Miva to work towards better security, although they did not offer any > timelines. They did not mention working with other vendors of other shopping > carts, nor did they admit the problem exists with other shopping cart apps. > Their only current solution is to educate their customers regarding the risks > and encourage them to upgrade to the more secure (and costly) PayFlow Pro > product. > > WHAT I DON'T KNOW: I don't know what other shopping cart applications (if any, > besides Miva's) are vulnerable. But I am highly suspicious that others are > because the problem seems to be that the PayFlow Link app does not offer any > credentials so that the receiving shopping cart app can validate the source of > the data. I also have not verified any other version of Miva Merchant besides > 3.x. Merchant 4.x is the most current version, but I think it uses the same > PayFlow Link module and so it should be vulnerable as well. I would be > interested in working with others that have access to other shopping cart apps > that can interface with PayFlow Link. > > PS - my first post to bugtraq, so I hope I did it right. Please let me know if > I've left anything off. > > -- > keith royster > keith@theroysters.com > > > > >
