In Qt through 5.14.1, the WebSocket implementation accepts up to 2GB for frames and 2GB for messages. Smaller limits cannot be configured. This makes it easier for attackers to cause a denial of service (memory consumption).
The Google V8 engine, as used in Google Chrome before 44.0.2403.89 and QtWebEngineCore in Qt before 5.5.1, allows remote attackers to cause a denial of service (memory corruption) or execute arbitrary code via a crafted web site.
The GIF decoder in QtGui in Qt before 5.3 allows remote attackers to cause a denial of service (NULL pointer dereference) via invalid width and height values in a GIF image.
The XMLHttpRequest object in Qt before 4.8.4 enables http redirection to the file scheme, which allows man-in-the-middle attackers to force the read of arbitrary local files and possibly obtain sensitive information via a file: URL to a QML application.
The QSharedMemory class in Qt 5.0.0, 4.8.x before 4.8.5, 4.7.x before 4.7.6, and other versions including 4.4.0 uses weak permissions (world-readable and world-writable) for shared memory segments, which allows local users to read sensitive information or modify critical program data, as demonstrated by reading a pixmap being sent to an X server.
QSslSocket in Qt before 4.7.0-rc1 recognizes a wildcard IP address in the subject's Common Name field of an X.509 certificate, which might allow man-in-the-middle attackers to spoof arbitrary SSL servers via a crafted certificate issued by a legitimate Certification Authority.