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Research > Zero-Day Tracker > 20130828

iOS and OS X Unicode Core Text Remote Denial of Service

Date Disclosed:

Date Patched:

Apple Inc.

Affected Software:
iOS 6 and OS X 10.8

A remotely exploitable denial of service condition exists when parsing a specific Unicode character sequence (Arabic: \u062E \u0337\u0334\u0310\u062E). The latest versions of OS X and iOS are affected. Core Text, which is utilized by Apple operating systems, handles the displaying of text and font. A segmentation fault is triggered when handing the aforementioned Unicode string, causing software utilizing Core Text to crash or quit ungracefully. This can be used by attackers to take down large numbers of iOS devices in crowded areas by broadcasting SSIDs that contain the malicious Unicode sequence. Additionally, this was used in the wild on Twitter and Facebook to crash OS X web browsers and iOS applications that interact with Twitter and Facebook. Facebook has blocked the Unicode string from being disseminated. 


Code Execution:

Denial of Service
Attackers may leverage this vulnerability to cause iOS applications, such as Messages and Twitter, to crash by Tweeting the malcious string, or sending SMS and iMessages to iOS devices. Additionally, attackers may name WFfi access points (SSIDs) using the malicious Unicode string, causing nearby iOS devices to reboot and OS X machines to experience application instability or system instability when the malicious SSID is displayed on screen (when joining WiFi networks, or after enabling WiFi). 

No mitigations currently available at this time.

 BeyondTrust's Retina® Network Security Scanner scans devices to detect for this vulnerability.

  • 31196 - Apple Mac OS X 10.9 Update - (20131022)
  • 31405 - Apple iOS 7 Update (20130918)


2013-08-28: Vulnerability publicly disclosed.
2013-09-18: Apple releases iOS 7
2013-10-22: Apple releases OS X 10.9

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