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The Spanish banking giant Santander has downplayed growing concerns over its alleged inclusion of "sensitive data" in its cookies.

The bank did not deny including personal data in cookies.

He claims that Santander online banking "unnecessarily stores sensitive information within cookies". Depending on which areas of online banking the customer uses, he claims this data allegedly includes the user's name, PAN (credit card number), bank account number and sort code, Alias and UserID.

"Of particular concern is the full PAN, which PCI DSS states should be rendered unreadable anywhere it is stored," the whistleblower stated.

He adds that he had gone public after experiencing problems getting the bank to play attention to (now fixed) cross-site scripting problems he had previously unearthed on its website.

The source alleges that Santander is violating its own cookie policy, which states that session cookies "do not contain personal information, and cannot be used to identify you" as well as the credit card industry's PCI DSS regulations (PDF).

Santander issued a statement strongly denying allegations that anything was amiss. It said that data stored in its cookies posed no risk to account security.

The data items stored within our cookies, if compromised, would not allow access to our online services on their own and our primary login processes do not rely on cookie data.

We review the use of our cookies and the data contained within them, and if necessary will review the IDs used by our customers to limit any future risks.

We take the security of our customer data very seriously. Customers can change their IDs at any time themselves and are reminded not to use the 'remember me' function on public or shared computers.

The Full Disclosure critic argues that Santander's handling of cookies does pose a risk, in cases where customers fail to close their browser after an e-banking session. "Additionally, whilst the cookies expire at the end of a session, they are not overwritten on logout," he explains. "This mean any user who does not close their browser, even if they log out correctly, will still have these cookies present until they close their browser, [t]hus increasing the window for exposure."

In the UK, Santander is the third biggest bank and a major provider of mortgages, with a combined total of more than 25 million British customers. The Full Disclosure posting was brought to our attention by three Reg readers who described it as unverified but potentially noteworthy. ®

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