The getImageData function in the ImageBufferCairo class in WebCore/platform/graphics/cairo/ImageBufferCairo.cpp in WebKit, as used in WebKitGTK+ prior to version 2.20.3 and WPE WebKit prior to version 2.20.1, is vulnerable to a heap-based buffer overflow triggered by an integer overflow, which could be abused by crafted HTML content.
http://packetstormsecurity.com/files/148200/WebKitGTK-Data-Leak-Code-Execution.html
https://security.gentoo.org/glsa/201808-04
https://usn.ubuntu.com/3687-1/