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CVE-2021-41816

Vulnerability in cgi (CVE-2021-41816)

Summary

Vulnerability in cgi (CVE-2021-41816). Successful exploitation can lead to full system takeover. Mitigation: upgrade to 0.1.0.1 or later.

Original description

The description as published by the source.

A buffer overrun vulnerability was discovered in CGI.escape_html. This can lead to a buffer overflow when a user passes a very large string (> 700 MB) to CGI.escape_html on a platform where long type takes 4 bytes, typically, Windows.

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-2021-41816 has been found in cgi.
Successful exploitation can lead to full system takeover.
What to do: upgrade cgi to 0.1.0.1 or later.
If unsure, ask your IT team or search "cgi CVE-2021-41816" on the vendor's site.

CVE-2021-41816 (cgi) — CWE-190
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Patched: 0.1.0.1 — 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-190) exists in cgi.

📍 Affected scope

Check the vendor advisory for the affected versions of cgi.

🔥 Severity

Severity: ?. Successful exploitation can lead to full system takeover.

🔧 How to fix

Update to 0.1.0.1.

🛡️ 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 'cgi' . 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 'cgi' . | 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 cgi 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 cgi to 0.1.0.1

    ステージング環境で 0.1.0.1 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

RubyGems cgi
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.1.0.1"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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