Ruby before 2.2.10, 2.3.x before 2.3.7, 2.4.x before 2.4.4, 2.5.x before 2.5.1, and 2.6.0-preview1 allows an HTTP Response Splitting attack. An attacker can inject a crafted key and value into an HTTP response for the HTTP server of WEBrick. It was found that WEBrick did not sanitize headers sent back to clients, resulting in a response-splitting vulnerability. An attacker, able to control the server's headers, could force WEBrick into injecting additional headers to a client.
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