Weird characters in URL
In my webserver when user requests URLs with weird characters, I remove these characters. And system logs these cases. When I check sanitized cases I found these. I'm curious that what would be the objective of these URLs ?
I check the IPs and these are real people and uses website as a normal person. But 1 time in their 20 URL requets of these people, URL has these weird characters at last.
http://example.com/@%EF%BF%BD%EF%BF%BD%02?o=3&g=&s=&z=%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%3E?, agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Firefox/31.0,
http://example.com/%60E%EF%BF%BD%02?o=3&g=&s=&z=%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%3E?, agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Firefox/31.0
http://example.com/%60E%EF%BF%BD%02?o=3&g=&s=&z=%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%3E?, agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Firefox/31.0
http://example.com/p%EF%BF%BD%1D%01?o=3&g=&s=&z=%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%3E?, agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Firefox/31.0
http://example.com/%EF%BF%BDC%EF%BF%BD%02?o=3&g=&s=&z=%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%3E?, agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Firefox/31.0
http://example.com/%EF%BF%BDR%EF%BF%BD%02?o=3&g=&s=&z=%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD`%EF%BF%BD%EF%BF%BD%7F, agent: Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/36.0.1985.125 Safari/537.36
http://example.com/%EF%BF%BDe%EF%BF%BDv8%01%EF%BF%BD?o=3&g=P%01%EF%BF%BD&s=&z=%EF%BF%BD%EF%BF%BD%15%01%EF%BF%BD%EF%BF%BD, agent: Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/35.0.1916.114 Safari/537.36
http://en.wikipedia.org/wiki/Specials_(Unicode_block)
They are essentially malformed URLs. They can be generated from a specific malware that is trying to exploit web site vulnerabilities, from malfunctioning browser plugin or extension, or from a bug in a JS file (i.e. tracking with Google Analytics) in combination with a specific browser version/operating system. In any case, you can't actually control what requests will come from a client and there's nothing you can do to stop that so, if your generated HTML/JS code is correct, you have done your work.
If you like to correct those URLs for any reason, you can enable URL rewriting and set a rule with a regular expression filter to transform those URLs to valid URLs. Anyway, I don't suggest do that: the web server should respond with a error 404 page not found message, because that is the standard (it's a client error, after all), and this is in my opinion a faster and safer method than applying URL rewriting. (rewriting procedure may contains bugs, so someone can try to exploit that, etc, etc)
For sake of curiosity, you can easily decode those URLs with an online URL decoder of your choice (i.e. this), but essentially you will discover what you already know: there are a lot of UTF-8 replacement characters in those URLs.
In fact, %EF%BF%BD is the url-encoded version of the hex representation of the 3 bytes (EF BF BD) of the UTF-8 replacement character. You can see that character also as � or EF BF BD or FFFD or ï ¿ ½, and so on, depending of the representation method you choose.
Also, you can check by your own how the client handles that character. Go here:
http://www.cogsci.ed.ac.uk/~richard/utf-8.cgi?input=%EF%BF%BD&mode=char
press the GO button and, using your browser developer tools, check what really happens: the browser is actually encoding the unknown character with %EF%BF%BD before sending it to the web server.
These look like corrupted URLs being inserted by a piece of Malware/Adware called "Adpeak".
Here are some details on Adpeak:
How to remove AdPeak lqw.me script from my web pages?
Adpeak has a client side component that sticks the following tag into web pages:
<script type="text/javascript" id="2f2a695a6afce2c2d833c706cd677a8e" src="http://d.lqw.me/xuiow/?g=7FC3E74A-AFDA-0667-FB93-1C86261E6E1C&s=4150&z=1385998326"></script>
Adpeak also sometimes uses the host names "d.sitespeeds.com", "d.jazzedcdn.com", "d.deliversuper.com", "d.blazeapi.com", "d.quikcdn.com", probably others. Here are a few more examples:
<script type="text/javascript" id="2f2a695a6afce2c2d833c706cd677a8e" src="http://d.deliversuper.com/xuiow/?o=3&g=823F0056-D574-7451-58CF-01151D4A9833&s=7B0A8368-1A6F-48A5-B236-8BD61816B3F9&z=1399243226"></script>
<script type="text/javascript" id="2f2a695a6afce2c2d833c706cd677a8e" src="http://d.jazzedcdn.com/xuiow/?o=3&g=B43EA207-C6AC-E01B-7865-62634815F491&s=B021CBBD-E38E-4F8C-8E93-6624B0597A23&z=1407935653"></script>
<SCRIPT id=2f2a695a6afce2c2d833c706cd677a8e type=text/javascript src="http://d.lqw.me/xuiow/?o=3&g=87B35A3E-C25D-041E-0A0F-C3E8E473A019&s=BBA5481A-926B-4561-BD79-249F618495E6&z=1393532281"></SCRIPT>
<SCRIPT id=2f2a695a6afce2c2d833c706cd677a8e type=text/javascript src="http://d.lqw.me/xuiow/?o=2&g=0AD3E5F2-B632-382A-0473-4C994188DBBA&s=9D0EB5E9-CCC9-4360-B7CA-3E645650CC53&z=1387549919"></SCRIPT>
The "id" is consistent: it's always "2f2a695a6afce2c2d833c706cd677a8e" in the cases we've seen.
There's always a "g", "s", and "z" parameter, and sometimes a "o" parameter that has values of 2 or 3.
We've noticed that with our pages, a certain version of this script is 100% correlated with seeing corrupted characters in the DOM: if "o" is omitted or set to 2, we'll see a Unicode FFFD injected near the end of the page or sometimes a Ux000E character, a.k.a. SHIFT OUT, which blows up standard JSON/XML serialization libraries, which is why we've been researching these URLs. We've never seen a corruption for "o=3"
However, sometimes it looks like Adpeak gets confused, and inserts junk like this:
<script type="text/javascript" id="2f2a695a6afce2c2d833c706cd677a8e" src="��?o=3&g=&s=&z=����������~?"></script>
Now, we don't know that this is Adpeak, because the URLs are mangled, but the "o=3", "g", "s", and "z" parameters are four smoking guns. The host is missing here, so it will resolve against our server, so these UxFFFDs will get sent up as UTF-8 hex-encoded "%EF%BF%BD" sequences, which are identical to what people have been seeing above.
If you're curious about how common this is, for a particular customer with high traffic and a wide demographic, we see Adpeak URLs injected into about 1.09% of their web pages, both well-formed Adpeak URLs as well as URLs with UxFFFD's. If you just look for Adpeak URLs with UxFFFD sequences, those appear in 0.053% of all web pages. And if you just look for Adpeak URLs that cause DOM corruptions (e.g., the valid URLs that contain "o=2" or no "o" parameter), that covers 0.20% of all web pages.
Probably your site's character-set is not initialized to UTF-8, but when you request a page in the site it thinks that the character are encoded with utf-8. When it "understands" that the characters are not encoded in UTF-8 format, it replaces any character that it doesn't know with the bytes sequence EF BF BD ("character place keeper").
Make sure you use UTF-8 in everyplace in your site by using <meta charset="UTF-8"> in every page.
Another example for this in a different situation: Whats going on with this byte array?