CVE intelligence and bounded remediation

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

Medium CVSS 6.5

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.

Severity
Medium
CVSS
6.5 (3.1)
Published
2021-03-15
CISA KEV
Not currently listed
Ecosystem
python/pypi
Weaknesses
CWE-295

Affected products

  • python / urllib3
  • fedoraproject / fedora / 34
  • oracle / peoplesoft_enterprise_peopletools / 8.59

Matched remediation archetype

Cryptography, certificate, signature, and channel validation

This catalog composition supplies bounded fallback guidance. Explicitly reviewed curated workflows load with the complete record below.

Check exposure

  • Inventory affected algorithms, key uses, trust stores, certificate validation settings, random sources, and plaintext channels across clients and services.
  • Determine which secrets, identities, signatures, or data protections depend on the affected primitive or validation path.
  • Check debug, compatibility, fallback, and hostname or audience override settings in build and runtime configuration.

Remediate safely

  • Use a maintained platform cryptographic API with approved algorithms, modes, parameters, randomness, and full peer identity validation.
  • Remove insecure fallback and validation bypasses; separate keys by purpose and load them from managed secret storage.
  • Plan rotation or reissuance for affected keys, certificates, tokens, hashes, or ciphertext and document compatibility sequencing.

Authoritative sources

Complete CVE record and remediation plan

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