The memory corruption vulnerability in Mozilla's flagship, open-source browser exists due to a flaw in the way Firefox handles freed data structures modified in the onUnload event handler, according to a U.S.-CERT advisory. That flaw can cause a memory corruption error.
Mozilla's security update, which was released last week, does fix the memory corruption issue, though the company had not made that public initially.
"The Firefox 18.104.22.168 update includes fixes for the bugs that researcher Michal Zalewski reported last week, including the hostname vulnerability, cookie issue and memory corruption issue," wrote Window Snyder, Mozilla's chief security officer, in an e-mail to InformationWeek. "Due to the security fixes, we strongly recommend that all Firefox users upgrade to this latest release." The upgrade is available at this Web site.