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.
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Wed, 14 Oct 2026 12:30:00 +0000
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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
No data.
Status : Modified
Published: 2021-03-15T18:15:19.017
Modified: 2026-10-14T12:17:11.087
Link: CVE-2021-28363