The is_a function in PHP 5.3.7 and 5.3.8 triggers a call to the __autoload function, which makes it easier for remote attackers to execute arbitrary code by providing a crafted URL and leveraging potentially unsafe behavior in certain PEAR packages and custom autoloaders.
include/iniset.php in Roundcube Webmail 0.5.4 and earlier, when PHP 5.3.7 or 5.3.8 is used, allows remote attackers to trigger a GET request for an arbitrary URL, and cause a denial of service (resource consumption and inbox outage), via a Subject header containing only a URL, a related issue to CVE-2011-3379.
The parse_str function in (1) PHP, (2) Hardened-PHP, and (3) Suhosin, when called without a second parameter, might allow remote attackers to overwrite arbitrary variables by specifying variable names and values in the string to be parsed. NOTE: it is not clear whether this is a design limitation of the function or a bug in PHP, although it is likely to be regarded as a bug in Hardened-PHP and Suhosin.