Cloudflare suddenly started to reject PUT requests with no Content-Length header with HTTP error 411.
What steps have you taken to resolve the issue?
Turning the proxy off resolves the issue, but this is not a solution.
Also including a Content-Length header with value of 0 fixes the problem, but this is not a solution either for third-party requests.
What are the steps to reproduce the issue?
Send a PUT request with empty body and no Content-Length header.
This was never an issue up until this Tuesday (15 April). Since then Cloudflare started to reject PUT / POST requests with no body. Some libraries do not include the Content-Length header when the request lacks a body, and this is a valid scenario. So Cloudflare should just continue to forward these requests to origin, instead of rejecting them with 411.
Yes, the origin servers run on IIS. And that works fine if the requests hit those directly. However origin servers are proxied through Cloudflare, and this is where we’re getting the 411 errors.
DYNAMIC means the error is coming from your server.
Im not familiar with IIS, but someone else had the same problem some time ago, and it turned out the requests were blocked by http.sys, which is a part of IIS or Windows server maybe?
And don’t take this wrong, it might still be related to a recent Cloudflare update, but the logs from the server side might help narrow down where the problem lies.
I have the same problem…
Suddenly cloudflare proxied api endpoint (PUT) started to return 411 Length Required error (for empty body PUT, with Content-Length: 0). It works fine without proxy (I can use direct url and it works), I did not change anything regarding backend (GCP Cloud run) and cloudflare. I don’t see the traffic in my backend access logs, that’s why it seems cloudflare blocked the request
No, it seems the errors in HTTPERR are intermittent. Most of the time nothing landed in there, so I assumed Cloudflare proxy is doing some magic. Meanwhile we patched the code that is under our control to send an empty JSON as body - {}, instead of an empty body. And hoping the issue will go away on its own, the same way that it appeared
Hi! We are facing the same problem. It started to occur recently. Symptoms are the same: when browser or any other http client (we tried curl) sends POST or PUT request with empty body and a header content-length: 0 and this request is reverse-proxied by Cloudflare to our server, the header content-length: 0 disappears. Our web server is IIS which runs on Windows Server. This request can’t reach it, because it is denied by HTTP.SYS which replies with 411 Length Required.
The only thing we figured out is that this problem depends on used HTTP protocol version. Our web server supports HTTP/2 and HTTP/1.1 protocols. So, when the client sends request using HTTP/3, Cloudflare transforms request to our server using HTTP/2 and this works fine, the header remains in place. But when we try to send request using HTTP/2 the header disappears. Here are our test commands:
This one works fine:
curl -v -X PUT -H "Content-Length: 0" "https://our-site-url" --http3
These two returned 411:
curl -v -X PUT -H "Content-Length: 0" "https://our-site-url" --http2
curl -v -X PUT -H "Content-Length: 0" "https://our-site-url" --http1.1
We clearly see in verbose output that content-length header was supplied:
* [HTTP/2] [1] OPENED stream for https://our-site-url
* [HTTP/2] [1] [:method: PUT]
* [HTTP/2] [1] [:scheme: https]
...
* [HTTP/2] [1] [user-agent: curl/8.13.0]
* [HTTP/2] [1] [accept: */*]
* [HTTP/2] [1] [content-length: 0]
> PUT /our-site-url HTTP/2
> Host: our-host
> User-Agent: curl/8.13.0
> Accept: */*
> Content-Length: 0
>
* Request completely sent off
< HTTP/2 411
< date: Thu, 24 Apr 2025 17:04:11 GMT
< content-type: text/html; charset=us-ascii
< server: cloudflare
< cf-cache-status: DYNAMIC
< cf-ray: 93572da9efe621d7-AMS
< alt-svc: h3=":443"; ma=86400
<
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN""http://www.w3.org/TR/html4/strict.dtd">
<HTML><HEAD><TITLE>Length Required</TITLE>
<META HTTP-EQUIV="Content-Type" Content="text/html; charset=us-ascii"></HEAD>
<BODY><h2>Length Required</h2>
<hr><p>HTTP Error 411. The request must be chunked or have a content length.</p>
</BODY></HTML>
There are no other proxies between our client and server except Cloudflare.
