curl 7.1.1 to and including 7.75.0 is vulnerable to an "Exposure of Private Personal Information to an Unauthorized Actor" by leaking credentials in the HTTP Referer: header. libcurl does not strip off user credentials from the URL when automatically populating the Referer: HTTP request header field in outgoing HTTP requests, and therefore risks leaking sensitive data to the server that is the target of the second HTTP request.

curl 7.41.0 through 7.73.0 is vulnerable to an improper check for certificate revocation due to insufficient verification of the OCSP response.

A flaw was found in the way libcurl handled TLS 1.3 session tickets. A malicious HTTPS proxy could possibly use this flaw to make libcurl resume a TLS session it previously had with the proxy while intending to resume a TLS session with a target server, making it possible for the proxy to perform a man-in-the-middle attack.