CVE-2021-28363

Name: CVE-2021-28363
Creator: NVD / NIST
Published: 2021-03-15T18:15:19.017+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 6.5/10EPSS 2.11%

Last modified Jun 17, 2026

CVE-2021-28363 is a medium-severity vulnerability rated 6.5/10 on the CVSS scale. 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. EPSS estimates a 2.11% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

6.5/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

EPSS Probability

2.11%

79.4th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-295

Affected Software

Vendor	Product	Versions
Python	Urllib3	>= 1.26.0, < 1.26.4
Fedoraproject	Fedora	34
Oracle	Peoplesoft Enterprise Peopletools	8.59

References

https://github.com/urllib3/urllib3/commit/8d65ea1ecf6e2cdc27d42124e587c1b83a3118b0Patch, Third Party Advisory
https://github.com/urllib3/urllib3/commits/mainPatch, Third Party Advisory
https://github.com/urllib3/urllib3/security/advisories/GHSA-5phf-pp7p-vc2rMitigation, Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/4S65ZQVZ2ODGB52IC7VJDBUK4M5INCXL/
https://pypi.org/project/urllib3/1.26.4/Third Party Advisory
https://security.gentoo.org/glsa/202107-36Third Party Advisory
https://security.gentoo.org/glsa/202305-02
https://security.netapp.com/advisory/ntap-20240621-0007/
https://www.oracle.com/security-alerts/cpuoct2021.htmlPatch, Third Party Advisory
https://github.com/urllib3/urllib3/commit/8d65ea1ecf6e2cdc27d42124e587c1b83a3118b0Patch, Third Party Advisory
https://github.com/urllib3/urllib3/commits/mainPatch, Third Party Advisory
https://github.com/urllib3/urllib3/security/advisories/GHSA-5phf-pp7p-vc2rMitigation, Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/4S65ZQVZ2ODGB52IC7VJDBUK4M5INCXL/
https://pypi.org/project/urllib3/1.26.4/Third Party Advisory
https://security.gentoo.org/glsa/202107-36Third Party Advisory
https://security.gentoo.org/glsa/202305-02
https://security.netapp.com/advisory/ntap-20240621-0007/
https://www.oracle.com/security-alerts/cpuoct2021.htmlPatch, Third Party Advisory

Timeline

Published: Mar 15, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-28363?

How severe is CVE-2021-28363?

CVE-2021-28363 has a CVSS score of 6.5/10 (MEDIUM severity). The EPSS model estimates a 2.11% probability of exploitation in the next 30 days.

How do I fix CVE-2021-28363?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-28363?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST