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CVE-2021-28363 medium CVSS 6.5

Vulnerability in urllib3 (CVE-2021-28363)

Summary

Vulnerability in urllib3 (CVE-2021-28363). Risk of unauthorized operations or information disclosure. Mitigation: upgrade to 1.26.4 or later.

Original description

The description as published by the source.

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.

Source: OSV.dev (Open Source Vulnerabilities) NVD GitHub Advisory OSV

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2021-28363 has been found in urllib3.
Risk of unauthorized operations or information disclosure. CVSS score: 6.5/10.
What to do: upgrade urllib3 to 1.26.4 or later.
If unsure, ask your IT team or search "urllib3 CVE-2021-28363" on the vendor's site.

CVE-2021-28363 (urllib3) — CWE-295 / CVSS v3 6.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Patched: 1.26.4 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (CWE-295) exists in urllib3.

📍 Affected scope

Check the vendor advisory for the affected versions of urllib3.

🔥 Severity

Severity: Medium (CVSS 6.5/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 1.26.4.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'urllib3' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r 'urllib3' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で urllib3 を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade urllib3 to 1.26.4

    ステージング環境で 1.26.4 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

PyPI urllib3
[{"type":"ECOSYSTEM","events":[{"introduced":"1.26.0"},{"fixed":"1.26.4"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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