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IIS acting as reverse proxy: Where the problems start

pcociuba's avatar
pcociuba
Icon for Microsoft rankMicrosoft
Sep 10, 2019
This is the second article in a three-part series of articles dealing with setting up IIS as a reverse proxy. Check out part one here.   Testing this new setup for basic scenarios may work, but y...
Updated Sep 10, 2019
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pcociuba's avatar
pcociuba
Icon for Microsoft rankMicrosoft
Dec 20, 2019

Hello TomyVO,

 

The issue here is plainly explained in the status code that IIS issues when handling this request: namely 404.11. Checking the IIS status codes as detailed in the documentation (http://linqto.me/IISCodes) the meaning of this status code is: request contains double escape sequence. The sequence would be the part in bold in the request excerpt you pasted:


2019-11-06 15:52:52 192.168.1.253 GET /media/show/1%2Fa%2F0%2F1%2F1a010a9833862e5745c20d12db63f4c3b72f8ff4_VER12220_Pharma_pack_Fles_glas_all_round_bruin_15_ml.jpg/thumbnail_small - 443 - 81.241.239.118 Mozilla/5.0+(Windows+NT+10.0;+Win64;+x64)+AppleWebKit/537.36+(KHTML,+like+Gecko)+Chrome/77.0.3865.120+Safari/537.36 https://undisclosed.be/ 404 11 0 9

 

What we would have to ask is: how was this link generated by your backend server? Was the backend server that doubly escaped the file? If so, the problem is on the backend server. If not what you can try and do is gather a FREB trace for a 404.11 status code and see if the url that is requested by the client is not somehow rewritten by url rewrite.