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.

Heap-based buffer overflow in the Lookup_MarkMarkPos function in the HarfBuzz module (harfbuzz-gpos.c), as used by Qt before 4.7.4 and Pango, allows remote attackers to cause a denial of service (crash) and possibly execute arbitrary code via a crafted font file.