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From: "Christoph M. Becker" <cmbecker69@arcor.de>
Newsgroups: comp.lang.javascript
Subject: Re: Javascript injection
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Date: Wed, 31 Aug 2016 12:43:42 +0200
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On 31.08.2016 at 10:25, Evertjan. wrote:

> Aleksandro <aleksandro@gmx.com> wrote on 30 Aug 2016 in 
> comp.lang.javascript:
> 
>> On 29/08/16 12:10, Evertjan. wrote:
>>> Hans-Georg Michna <hans-georgNoEmailPlease@michna.com> wrote on 29 Aug
>>> 2016 in comp.lang.javascript: 
>>>
>>>> On Sun, 28 Aug 2016 22:58:08 -0700 (PDT),
>>>> bit-naughty@hotmail.com wrote:
>>>>
>>>>> If I have a "forum" type of site, where stuff is being posted, and
>>>>> stored in the backend (in a MySQL database, using PHP), say,....can
>>>>> anyone type in Javascript into the post to accomplish naughty things?
>>>>> What's the most nefarious thing anyone can do? All I can think of is
>>>>> that someone would deface the page somehow, that *that* post is on,
>>>>> which, really, I can't see the point of..... Anything else? ...and how
>>>>> do I protect against it? (the post will probably be displayed inside a
>>>>> DIV on the page, I think....) 
>>>>
>>>> I would not even allow ordinary users to enter HTML tags, i.e.
>>>> have them filtered out. This, of course, includes <script ...>
>>>> tags, so users cannot inject any script.
>>>
>>> theText = theText.replace(/</g,'&lt;');
>>
>> Serversidely OT: http://php.net/str_replace
> 
> You better [for this NG] use ASP + Jscript, making my suggestion ON topic.

ACK.  However, the OP mentions:

| If I have a "forum" type of site, where stuff is being posted, and
| stored in the backend (in a MySQL database, using PHP) […]

Therefore this newsgroup is somewhat OT anyway.  Therefore, FUP2 c.l.php.

BTW: don't use str_replace() in this case; use htmlspecialchars() with
the appropriate $encoding.  Consider to also use strip_tags().

-- 
Christoph M. Becker