Affected: https://github.com/curl/curl

An improper certificate validation vulnerability exists in curl <v8.1.0 in the way it supports matching of wildcard patterns when listed as "Subject Alternative Name" in TLS server certificates. curl can be built to use its own name matching function for TLS rather than one provided by a TLS library. This private wildcard matching function would match IDN (International Domain Name) hosts incorrectly and could as a result accept patterns that otherwise should mismatch. IDN hostnames are converted to puny code before used for certificate checks. Puny coded names always start with `xn--` and should not be allowed to pattern match, but the wildcard check in curl could still check for `x*`, which would match even though the IDN name most likely contained nothing even resembling an `x`.

Affected: Ubuntu:20.04:LTS: curl, Ubuntu:22.04:LTS: curl

Hiroki Kurosawa discovered that curl incorrectly handled validating certain certificate wildcards. A remote attacker could possibly use this issue to spoof certain website certificates using IDN hosts. (CVE-2023-28321)

Hiroki Kurosawa discovered that curl incorrectly handled callbacks when certain options are set by applications. This could cause applications using curl to misbehave, resulting in information disclosure, or a denial of service. (CVE-2023-28322)

It was discovered that curl incorrectly handled saving cookies to files. A local attacker could possibly use this issue to create or overwrite files. This issue only affected Ubuntu 22.10, and Ubuntu 23.04. (CVE-2023-32001)