CVE-2023-28321

Published May 26, 2023

Last updated a year ago

CVSS medium 5.9
Libcurl

Overview

Description
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`.
Source
support@hackerone.com
NVD status
Modified

Risk scores

CVSS 3.1

Type
Primary
Base score
5.9
Impact score
3.6
Exploitability score
2.2
Vector string
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
Severity
MEDIUM

Weaknesses

support@hackerone.com
CWE-295
nvd@nist.gov
CWE-295

Social media

Hype score
Not currently trending

Configurations

Related CVEs

  1. curl would wrongly reuse an existing HTTP proxy connection doing CONNECT to a server, even if the new request uses different credentials for the HTTP proxy. The proper behavior is to create or use a separate connection.•CVE-2026-3784
  2. When doing a second SMB request to the same host again, curl would wrongly use a data pointer pointing into already freed memory.•CVE-2026-3805
  3. libcurl can in some circumstances reuse the wrong connection when asked to do an Negotiate-authenticated HTTP or HTTPS request. libcurl features a pool of recent connections so that subsequent requests can reuse an existing connection to avoid overhead. When reusing a connection a range of criterion must first be met. Due to a logical error in the code, a request that was issued by an application could wrongfully reuse an existing connection to the same server that was authenticated using different credentials. One underlying reason being that Negotiate sometimes authenticates *connections* and not *requests*, contrary to how HTTP is designed to work. An application that allows Negotiate authentication to a server (that responds wanting Negotiate) with `user1:password1` and then does another operation to the same server also using Negotiate but with `user2:password2` (while the previous connection is still alive) - the second request wrongly reused the same connection and since it then sees that the Negotiate negotiation is already made, it just sends the request over that connection thinking it uses the user2 credentials when it is in fact still using the connection authenticated for user1... The set of authentication methods to use is set with `CURLOPT_HTTPAUTH`. Applications can disable libcurl's reuse of connections and thus mitigate this problem, by using one of the following libcurl options to alter how connections are or are not reused: `CURLOPT_FRESH_CONNECT`, `CURLOPT_MAXCONNECTS` and `CURLMOPT_MAX_HOST_CONNECTIONS` (if using the curl_multi API).•CVE-2026-1965
  4. URLs containing percent-encoded slashes (`/` or `\`) can trick wcurl into saving the output file outside of the current directory without the user explicitly asking for it. This flaw only affects the wcurl command line tool.•CVE-2025-11563
  5. When doing SSH-based transfers using either SCP or SFTP, and asked to do public key authentication, curl would wrongly still ask and authenticate using a locally running SSH agent.•CVE-2025-15224

References

Sources include official advisories and independent security research.