In Nim 1.2.4, the standard library httpClient is vulnerable to a CR-LF injection in the target URL. An injection is possible if the attacker controls any part of the URL provided in a call (such as httpClient.get or httpClient.post), the User-Agent header value, or custom HTTP header names or values.
In Nim 1.2.4, the standard library httpClient fails to properly validate the server response. For example, httpClient.get().contentLength() does not raise any error if a malicious server provides a negative Content-Length.