The urllib3 library 1.26.x before 1.26.4 for Python omits SSL certificate validation in some cases involving HTTPS to HTTPS proxies. The initial connection to the HTTPS proxy (if an SSLContext isn't given via proxy_config) doesn't verify the hostname of the certificate. This means certificates for different servers that still validate properly with the default urllib3 SSLContext will be silently accepted.
History

Wed, 14 Oct 2026 12:30:00 +0000

Type Values Removed Values Added
References

cve-icon MITRE

Status: PUBLISHED

Assigner: mitre

Published: 2021-03-15T00:00:00.000Z

Updated: 2026-10-14T11:39:31.637Z

Reserved: 2021-03-13T00:00:00.000Z

Link: CVE-2021-28363

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Modified

Published: 2021-03-15T18:15:19.017

Modified: 2026-10-14T12:17:11.087

Link: CVE-2021-28363

cve-icon Redhat

Severity : Moderate

Publid Date: 2021-03-15T00:00:00Z

Links: CVE-2021-28363 - Bugzilla