on-headers is a node.js middleware for listening to when a response writes headers. A bug in on-headers versions "<1.1.0" may result in response headers being inadvertently modified when an array is passed to "response.writeHead()". Users should upgrade to version 1.1.0 to receive a patch. Uses are strongly encouraged to upgrade to "1.1.0", but this issue can be worked around by passing an object to "response.writeHead()" rather than an array.