USN-4898-1: curl vulnerabilities

Viktor Szakats discovered that curl did not strip off user credentials from referrer header fields. A remote attacker could possibly use this issue to obtain sensitive information. (CVE-2021-22876) Mingtao Yang discovered that curl incorrectly handled session tickets when using an HTTPS proxy. A remote attacker in control of an HTTPS proxy could use this issue to bypass certificate checks and intercept communications. This issue only affected Ubuntu 20.04 LTS and Ubuntu 20.10. (CVE-2021-22890)