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Mike Cole avatar Server

Inconsistent 403 Forbidden issues with images on a website

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Mike Cole

I am getting inconsistent HTTP 403 Forbidden results when requesting images embedded on a webpage. This is happening more frequently in FireFox, but occasionally also happens in Chrome. This website has been used for many years and this just popped up a few weeks ago. I control both the website and the server and am not sure of how to troubleshoot this issue. When I refresh the page it seems to be a different combination of resources that causes the issue.

Response:

HTTP/1.1 403 Forbidden
Server: Microsoft-IIS/8.5
X-UA-Compatible: IE=Edge
X-Frame-Options: sameorigin
X-Content-Type-Options: nosniff
X-XSS-Protection: 1; mode=block
Strict-Transport-Security: max-age=63072000; includeSubDomains;
P3P: Our site does not have a P3P Policy, please see our privacy policy for more information.
Date: Fri, 15 Apr 2022 17:34:15 GMT
Content-Length: 0

Request:

GET /bonds/images/exclamation.png HTTP/1.1
Host: <Redacted>
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:99.0) Gecko/20100101 Firefox/99.0
Accept: image/avif,image/webp,*/*
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate, br
Connection: keep-alive
Referer: <Redacted>
Cookie: <Redacted>
Sec-Fetch-Dest: image
Sec-Fetch-Mode: no-cors
Sec-Fetch-Site: same-origin
If-Modified-Since: Mon, 04 Apr 2022 20:03:08 GMT
Cache-Control: max-age=0
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hr flag
basvdlei
It's just 1 server? No load-balancer sending some traffic to a wrong backend? Have you enabled server logging?: https://docs.microsoft.com/en-us/iis/manage/provisioning-and-managing-iis/configure-logging-in-iis
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et flag
SmallClanger
Focus on the whom what and when to start with. Does _everyone_ get 403s at the same time? If so, what times? (scan your logs for timestamps) When does it start working again? Are _some_ users are getting them _all_ of the time? Is it only specific images? Understanding the pattern can point you in the right direction. Perhaps some built-in rate-limiting on resource or source IP?
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Lex Li avatar
vn flag
Lex Li
You really need the help of FRT to learn more about the 403 errors, https://docs.microsoft.com/en-us/iis/troubleshoot/using-failed-request-tracing/troubleshooting-failed-requests-using-tracing-in-iis Without that no serious discussion can be made.
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Mike Cole avatar Server
bq flag
Mike Cole

In this case, it appears the issue was being caused by the dynamic IP restrictions limit, and increasing the max concurrent requests solved the issue.

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