Apache VCL versions 2.1 through 2.5 do not properly validate form input when processing a submitted block allocation. The form data is then used as an argument to the php built in function strtotime. This allows for an attack against the underlying implementation of that function. The implementation of strtotime at the time the issue was discovered appeared to be resistant to a malicious attack. However, all VCL systems running versions earlier than 2.5.1 should be upgraded or patched. This vulnerability was found and reported to the Apache VCL project by ADLab of Venustech.