String handling functions in Mozilla 1.7.3, Firefox 1.0, and Thunderbird
before 1.0.2, such as the nsTSubstring_CharT::Replace function, do not
properly check the return values of other functions that resize the string,
which allows remote attackers to cause a denial of service and possibly
execute arbitrary code by forcing an out-of-memory state that causes a
reallocation to fail and return a pointer to a fixed address, which leads
to heap corruption.