A new vulnerability makes it easier for fraudsters to pass off content from bogus websites as the real thing.

Using a variant of well-known cross site scripting attacks, British Web developer and security researcher Sam Greenhalgh was able to inject JavaScript from his own website into pages generated by NatWest, Mastercard and Barclays. Even the website of GCHQ, Britain's electronic eavesdropping operation, can be overlaid with bogus content, Greenhalgh shows.

Since the demo was first published late last month, MasterCard and Barclays have blocked the exploit route. This is just as well, as both have recently announced initiatives to combat phishing - apparently without ensuring that their own houses were in order. The continued vulnerability of other sites - such as NatWest's - is a cause for serious concern, because it could help fraudsters make their scams appear more plausible.

Security firm Netcraft warns: "Having the ability to run their code from the financial institution's own site is a big step forward for fraudsters, as it makes their attack much more plausible. It will almost certainly lead fraudsters to seek out banking sites vulnerable to cross site scripting as a refinement on current phishing attacks which depend upon obscuring the true location of a window prompting for bank account authentication details."

"The technique works equally well over SSL, and so offers fraudsters the enticing opportunity of having a phishing attack delivered over SSL with the attacker's code being served as part of a url from the bona fide bank's own secure server," it adds.

The attacks Greenhalgh demonstrates arise from well-documented cross site scripting security risks. Declaring a self interest, Netcraft advises companies to carry out more application testing. Other vendors promote digital certificates.

Steve Roylance, technical marketing director at security firm Comodo, told El Reg that the best way to defend against content injection threats is to bind the visual contents of a site to its website address using digital certificate technology. "CVC – Content Verification Certificates, a digital certificate binding these content and URL elements together is available from Comodo. Using our VEngine technology ,users are easily be able to spot this type of spoof," he claimed. ®

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