Integer overflow in the object_custom function in
ext/standard/var_unserializer.c in PHP before 5.4.34, 5.5.x before 5.5.18,
and 5.6.x before 5.6.2 allows remote attackers to cause a denial of service
(application crash) or possibly execute arbitrary code via an argument to
the unserialize function that triggers calculation of a large length value.

mdeslaur