Cloudflare Error 1041: Invalid Request Rewrite: Invalid Header Value
Error 1041 occurs when a Cloudflare Transform Rule sets a header to a value that violates HTTP header specifications. Header values must conform to RFC 7230 — they cannot contain certain control characters, null bytes, or newlines. If a dynamic expression in a Transform Rule produces a value with illegal characters, Cloudflare returns 1041 instead of forwarding the malformed request to the origin.
Status
Error 1041: Invalid Request Rewrite: Invalid Header ValueExample
GET /api/items HTTP/1.1
Host: www.example.com
User-Agent: Mozilla/5.0
Accept: text/htmlHTTP/1.1 409 Conflict
Server: cloudflare
CF-RAY: 7c9d0e1f2a3b4568-VNO
Content-Type: text/html
<!doctype html>
<html>
<head>
<title>www.example.com | Error 1041</title>
</head>
<body>
<h1>Error 1041: Invalid request rewrite: invalid header value</h1>
<p>A Cloudflare Transform Rule set a header to an invalid value. Please contact the site owner.</p>
</body>
</html>How to Troubleshoot
Check the header value expression
Review the Transform Rule's expression that generates the header value. Test what it evaluates to for the failing request.
Sanitize dynamic values
If the header value comes from a dynamic source (like a request field), ensure it is sanitized to remove control characters and newlines before setting it as a header.
URL-encode if necessary
If the header value must contain special characters, URL-encode them first so the raw header value contains only valid characters.
Common Causes
Expression produces invalid characters in header value
highThe Transform Rule's expression generates a value containing control characters (like \r, \n, \0) that are not allowed in HTTP headers.
Binary or encoded data in header
mediumThe rule tries to set a header value containing raw binary data or improperly encoded content that violates HTTP header formatting rules.
Empty header value where not allowed
lowThe expression evaluates to an empty string for a header that requires a non-empty value.
Related Error Codes
Invalid Request Rewrite: Header Modification Not Allowed
A Transform Rule attempted to modify a request header that Cloudflare does not allow to be changed.
Invalid Request Rewrite: Invalid URI Path
A Cloudflare Transform Rule or rewrite produced an invalid URI path.
Invalid Rewrite Rule: Failed to Evaluate Expression
A Cloudflare Transform Rule's expression could not be evaluated at runtime.
Frequently Asked Questions
This reference was compiled from official RFCs, protocol specifications, and hands-on troubleshooting experience. AI tools were used primarily for formatting and organizing the content on the page.