Multiple use-after-free vulnerabilities in WebKit, as used in Apple Safari before 4.1.3 and 5.0.x before 5.0.3, Google Chrome before 5.0.375.127, and webkitgtk before 1.2.6, allow remote attackers to execute arbitrary code or cause a denial of service (application crash) via vectors related to improper handling of MIME types by plug-ins.
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.