Description
The Zend Engine in PHP before 5.4.16 RC1, and 5.5.0 before RC2, does not properly determine whether a parser error occurred, which allows context-dependent attackers to cause a denial of service (memory consumption and application crash) via a crafted function definition, as demonstrated by an attack within a shared web-hosting environment. NOTE: the vendor's http://php.net/security-note.php page says "for critical security situations you should be using OS-level security by running multiple web servers each as their own user id.
Remediation
References
Related Vulnerabilities
Apache HTTP Server Uncontrolled Resource Consumption Vulnerability (CVE-2011-3192)
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Claroline Exposure of Sensitive Information to an Unauthorized Actor Vulnerability (CVE-2011-3716)