A cross-site scripting flaw on Twitter's website creates a means for posting code into updates, causing chaos across the network today.
The vulnerability allow messages to pop-up and third-party websites to open providing surfers move their cursor over a link, earning the flaw the nickname of onMouseOver. Thousands of Twitter accounts posted messages exploiting the flaw, mostly for fun and games, at least for now. Some users have begun exploiting the loophole to create tweets that contain blocks of colour (known as "rainbow tweets").
However the security weakness is just as easily exploited to redirect surfers to third-party websites containing malicious code, or to display spam advertising pop-ups.
Messages are also spreading virally that take advantage of the vulnerability for nefarious purposes. Victims include Sarah Brown, wife of the former British Prime Minister, whose Twitter profile has been messed around with to redirect surfers to a hard core porn site located in Japan, as explained in a blog post by Sophos here.
The flaw does not affect third-party Twitter clients but poses a serious risk on the Twitter.com website.
If you see a redacted (blacked out) tweet avoid clicking or moving your mouse over it, since these types of messages have been linked to the majority of exploits seen thus far.
"This is a very simple exploit but could have very damaging effects," said Jason Hart, senior European VP of CryptoCard. He warned that the bug might easily lend itself to phishing attacks.
Other researchers agreed with this assessment, arguing that Twitter ought to bring down the shutters on its website while it develops a fix.
Christopher Boyd, senior threat researcher at GFI Software, commented: "While there's a possibility that bad actors may use this to direct end-users to malware and phish pages, I'd like to think Twitter will have this under control before that happens. However, we are surprised that Twitter has not suspended the main twitter.com web site while it works on a fix."
Twitter said its was in the process of fixing the flaw. "We've identified and are patching a XSS attack; as always, please message @safety if you have info regarding such an exploit," it said, via the official @safety Twitter profile. ®