Qt 4 is a software toolkit that simplifies the task of writing and maintaining GUI applications for the X Window System. HarfBuzz is an OpenType text shaping engine. A flaw in the way Qt 4 expanded certain UTF-8 characters could be used to prevent a Qt 4 based application from properly sanitizing user input. Depending on the application, this could allow an attacker to perform directory traversal, or for web applications, a cross-site scripting attack. A buffer overflow flaw was found in the harfbuzz module in Qt 4. If a user loaded a specially-crafted font file with an application linked against Qt 4, it could cause the application to crash or, possibly, execute arbitrary code with the privileges of the user running the application. Users of Qt 4 should upgrade to these updated packages, which contain backported patches to correct these issues. All running applications linked against Qt 4 libraries must be restarted for this update to take effect.