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Vulnerabilities

Vulnerability · CVE-2021-28363

The urllib3 library 1.26.x before 1.26.4 for Python omits SSL certificate validation in some cases involving HTTPS to HTTPS proxies.

Published Mar 15, 2021 · catalog updated Oct 14, 2026 · The urllib3 library 1.26.x

Check if you run it

No confirmed exploitation is on record for CVE-2021-28363. EPSS is 2.17%. Act only if a listed version of The urllib3 library 1.26.x is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (The urllib3 library 1.26.x).
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
Medium6.5
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
2.17%
Remediation
Advisory link
Affected products
cpe fedoraproject/fedora · cpe oracle/peoplesoft enterprise peopletools · cpe python/urllib3

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.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • cpe fedoraproject/fedora34
  • cpe oracle/peoplesoft enterprise peopletools8.59
  • cpe python/urllib3version unspecified

How to fix CVE-2021-28363

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2021-28363. EPSS is 2.17%. Act only if a listed version of The urllib3 library 1.26.x is installed.

Which versions are affected?

Compare what you have installed with oracle/peoplesoft enterprise peopletools 8.59. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-295: Improper Certificate Validation. EPSS 2.17%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Mar 15, 2021 · NIST NVD

    Detected

    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 a

  2. Oct 14, 2026 · NIST NVD

    Updated

    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 a

Sources

  • CVE.orgVulnerability recordCVE-2021-28363

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2021-28363

    30-day exploitation probability 2.2%

    first.org
  • NIST NVDVulnerability recordCVE-2021-28363

    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 mean

    nvd.nist.gov

References

Freshness

Last verified in this catalog Oct 16, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.