505
HTTPSERVER_ERRORCritical5xx Server ErrorHIGH confidence
HTTP Version Not Supported
Production Risk
Very Low. This error is extremely rare in practice, as virtually all clients and servers have supported HTTP/1.1 for decades.
What this means
The HTTP version used in the request is not supported by the server. The response should contain a message describing why that version is not supported and what other protocols are.
Why it happens
- 1An old or misconfigured client is attempting to use an obsolete version of HTTP, like HTTP/0.9.
- 2A client is attempting to use a future, not-yet-supported version of HTTP.
- 3A bug in the client causes it to send a malformed HTTP version identifier.
How to reproduce
An ancient, automated script makes a request using the 'HTTP/1.0' protocol to a modern server that only supports HTTP/1.1 and HTTP/2.
trigger — this will error
trigger — this will error
GET / HTTP/1.0
expected output
HTTP/1.1 505 HTTP Version Not Supported
Fix
Update the Client
WHEN The client is using an outdated HTTP version.
Update the Client
Update the client software or library to one that supports a modern version of HTTP (e.g., HTTP/1.1 or later).
Why this works
Client-Side Upgrade
Sources
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