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Vulnerability of ASP.NET SignalR: Cross Site Scripting

Synthesis of the vulnerability 

An attacker can trigger a Cross Site Scripting of ASP.NET SignalR, in order to execute JavaScript code in the context of the web site.
Vulnerable software: IIS, .NET Framework, Visual Studio.
Severity of this announce: 2/4.
Creation date: 11/12/2013.
Références of this computer vulnerability: 2905244, BID-64093, CERTA-2013-AVI-669, CVE-2013-5042, MS13-103, VIGILANCE-VUL-13933.

Description of the vulnerability 

The ASP.NET SignalR library is used to establish a communication between a web browser and a web server, using JavaScript.

However, it does not filter received data before inserting them in generated HTML documents.

An attacker can therefore trigger a Cross Site Scripting of ASP.NET SignalR, in order to execute JavaScript code in the context of the web site.
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This threat impacts software or systems such as IIS, .NET Framework, Visual Studio.

Our Vigil@nce team determined that the severity of this computer threat is medium.

The trust level is of type confirmed by the editor, with an origin of document.

An attacker with a expert ability can exploit this cybersecurity bulletin.

Solutions for this threat 

ASP.NET SignalR: patch.
A patch is available in information sources.
The Microsoft announce indicates workarounds.
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