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.

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.

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.