How to put a set of special characters as a key value under appsettings tag in web.config file ?

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I want to put set of special characters as a key value under appsettings tag in web.config file.
Special characters to set as a key value - @"\|!#$%&()=?»«£§€{};'<>,+*^%"
i tried as below but it is not coming right

What I have tried:

Tried to set in web.config file under appsettings tag as a key value as below:

<add key="BlockedSpChacters" value=@"\|!#$%&()=?»«£§€{};'<>,+*^%"/>

Posted 11-Nov-21 2:54am

Member 15421351

Updated 11-Nov-21 2:58am

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Richard Deeming · Answer 1 · 2021-11-11T02:58:00

The config file is an XML file. Attribute values need to be encoded properly for XML.

Specifically, & needs to be encoded as &; < needs to be encoded as <; and > needs to be encoded as >.

You also can't use the C# "verbatim string" prefix (@) on the attribute value.

XML

<add key="BlockedSpChacters" value="\|!#$%&amp;()=?»«£§€{};'&lt;&gt;,+*^%"/>

NB: Your setting name makes me suspect that you're trying to filter out "bad" characters from values that you're injecting into a SQL query. If that's the case, stop immediately. Your code will be vulnerable to SQL Injection[^]. NEVER use string concatenation to build a SQL query. ALWAYS use a parameterized query.

Everything you wanted to know about SQL injection (but were afraid to ask) | Troy Hunt[^]
How can I explain SQL injection without technical jargon? | Information Security Stack Exchange[^]
Query Parameterization Cheat Sheet | OWASP[^]