In association with heise online

07 October 2011, 09:45

Developer function enables phishing at American Express

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Zoom An unprotected debugging function allows attackers to place arbitrary JavaScript code on the American Express web site
Security specialist Niklas Femerstrand has discovered a hole on the American Express web site that attackers can use to steal, among other things, the login data of credit card customers. The cross-site scripting (XSS) hole allows attackers to use manipulated links in order to write arbitrary JavaScript code into the victim's browser. The code is then executed in the context of the American Express web site. Attackers could read access credentials, steal cookies or inject malicious software onto the victim's system.

The vulnerability is found in a debugging function that is reachable over the Internet without further protection – and which is susceptible to cross-site scripting. The H's associates at heise Security were able to verify the vulnerability. Femerstrand says he was not able to contact the firm to report the problem because American Express does not list any contact details for security issues on its homepage. He therefore decided to publish complete details about the vulnerability in the hope of getting the firm to act.

The exposure of the flaw appears to have worked in terms of getting the charge card company to react. American Express has now removed the page and in a statement said that the page did not hold any card member information, such as card numbers or names; while accurate, the flaw was reported because it enabled phishing attacks, not because data was leaking from the page. The company also says it is unaware of any information that would indicate the hole was used for malicious purposes. It did not say, though, whether it was revising its processes for reporting security problems.


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