Yesterday, Russian researchers publicly disclosed the presence of a denial of service vulnerability affecting OS X 10.8 and iOS 6. OS X 10.9 Mavericks and iOS 7 are unaffected. So what’s the big deal with this particular denial of service vulnerability? It’s remotely exploitable and is trivial to trigger. Stringing together a series of Unicode characters, Arabic \u062E\u0337\u0334\u0310\u062E, and making a target display the characters triggers the vulnerability, causing applications to crash immediately.
Third party applications such as Chrome and Twitter (on both iOS and OS X), as well as iOS built-in applications like Messages, crash when displaying the above Unicode. Attackers may even create malicious SSIDs and broadcast them in public places. When a target user goes to join a WiFi network, turn on WiFi, or check their WiFi, the malicious SSID may be rendered by Core Text, a text and font layout and handling mechanism within OS X and iOS. The resulting segmentation fault in Core Text may cause instability in OS X, or even make an iOS device reboot.
Social media services have seen users posting, tweeting, and sharing the malicious Unicode string, prompting Facebook to ban the string from future posts. Having your Twitter feed blow up a Chrome tab isn’t the end of the world, but certainly worth mentioning as curious members of the public and script-kiddies everywhere will be having fun with this until a fix is released.