Archive_Tar through 1.4.10 allows an unserialization attack because phar: is blocked but PHAR: is not blocked.
Archive_Tar through 1.4.10 has :// filename sanitization only to address phar attacks, and thus any other stream-wrapper attack (such as file:// to overwrite files) can still succeed.
Impact
There is no impact; F5 products are not affected by this vulnerability.