The MITRE CVE dictionary describes this issue as:
The hb_buffer_ensure function in hb-buffer.c in HarfBuzz, as used in Pango 1.28.3, Firefox, and other products, does not verify that memory reallocations succeed, which allows remote attackers to cause a denial of service (NULL pointer dereference and application crash) or possibly execute arbitrary code via crafted OpenType font data that triggers use of an incorrect index.
Find out more about CVE-2011-0064 from the
MITRE CVE dictionary dictionary and
This issue did not affect the versions of qt shipped with Red Hat Enterprise Linux 4, 5 and 6.