USN-222-1 fixed a vulnerability in the Perl interpreter. It was
discovered that the version of USN-222-1 was not sufficient to handle
all possible cases of malformed input that could lead to arbitrary
code execution, so another update is necessary.
Jack Louis of Dyad Security discovered that Perl did not
sufficiently check the explicit length argument in format strings.
Specially crafted format strings with overly large length arguments
led to a crash of the Perl interpreter or even to execution of
arbitrary attacker-defined code with the privileges of the user
running the Perl program.
However, this attack was only possible in insecure Perl programs
which use variables with user-defined values in string
interpolations without checking their validity.