The last couple days, there’s been a virus spreading making use of yahoo mail’s interface. Usually web mail is considered a fairly safe way to get email, but in this case all that was done was the user clicking on a malicious email and the virus ran. It appears that javascript/AJAX/Web 2.0 applications are going to have to get closer scrutiny. In the Sans diary, they mention that they’ve analyzed javascript from several web applications and there are some that are vulnerable. (They’re contacting vendors.) They also point out web designers should keep this in mind as well..
The current worm could be readily modified to spread across many systems that do not escape javascript when displaying data from a foreign source. Many web developers should reexamine their code, and make sure that display functions do not deliver potentially malicious code.