Improper Certificate Validation Affecting urllib3 package, versions [1.26.0,1.26.4)



    Attack Complexity Low

    Threat Intelligence

    EPSS 0.14% (49th percentile)
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6.5 medium
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Red Hat
6.5 medium

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  • Snyk ID SNYK-PYTHON-URLLIB3-1085966
  • published 16 Mar 2021
  • disclosed 16 Mar 2021
  • credit Jorge, Quentin Pradet

How to fix?

Upgrade urllib3 to version 1.26.4 or higher.


urllib3 is a HTTP library with thread-safe connection pooling, file post, and more.

Affected versions of this package are vulnerable to Improper Certificate Validation. It 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 SSLContext will be silently accepted.