The HTTP header parsing code in Node.js 0.10.x before 0.10.42, 0.11.6 through 0.11.16, 0.12.x before 0.12.10, 4.x before 4.3.0, and 5.x before 5.6.0 allows remote attackers to bypass an HTTP response-splitting protection mechanism via UTF-8 encoded Unicode characters in the HTTP header, as demonstrated by %c4%8d%c4%8a.
The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.