{"cve":"CVE-2021-28363","nvd":{"published":"2021-03-15T18:15:19.017","modified":"2026-10-14T12:17:11.087","status":"Modified","description":"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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N","score":6.5},"cwes":["CWE-295"],"references":["https://github.com/urllib3/urllib3/commit/8d65ea1ecf6e2cdc27d42124e587c1b83a3118b0","https://github.com/urllib3/urllib3/commits/main","https://github.com/urllib3/urllib3/security/advisories/GHSA-5phf-pp7p-vc2r","https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/4S65ZQVZ2ODGB52IC7VJDBUK4M5INCXL/","https://pypi.org/project/urllib3/1.26.4/"],"products":["fedoraproject:fedora","oracle:peoplesoft_enterprise_peopletools","python:urllib3"],"source":"nvd","synced_at":"2026-10-19T21:15:50.279857260+00:00"},"epss":{"cve":"CVE-2021-28363","score":0.02166,"percentile":0.82127,"date":"2026-10-25"},"kev":null,"osv":[{"id":"GHSA-5phf-pp7p-vc2r","url":"https://osv.dev/vulnerability/GHSA-5phf-pp7p-vc2r","summary":"Using default SSLContext for HTTPS requests in an HTTPS proxy doesn't verify certificate hostname for proxy connection","modified":"2026-07-08T06:28:26.820684687Z","packages":[{"ecosystem":"PyPI","name":"urllib3","purl":"pkg:pypi/urllib3","ranges":[">=1.26.0 <1.26.4"],"fixed":["1.26.4"]}]},{"id":"PYSEC-2021-59","url":"https://osv.dev/vulnerability/PYSEC-2021-59","summary":"","modified":"2023-11-08T04:05:29.804412Z","packages":[{"ecosystem":"PyPI","name":"urllib3","purl":"pkg:pypi/urllib3","ranges":[">=1.26.0 <1.26.4"],"fixed":["1.26.4"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}