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CVE-2026-71554
medium
CVSS 5.3
Vulnerability in h2 (CVE-2026-71554)
Summary
vulnerability in h2 (CVE-2026-71554). Risk of unauthorized operations or information disclosure. Exploitable via `Host header`. Mitigation: upgrade to `4.4.1` or later.
AI summary snake-internal / snake-material-v2
A vulnerability tracked as **CVE-2026-71554** has been found in h2.
Attackers can target a specific entry point like `Host header` over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 5.3/10.
What to do: upgrade h2 to **4.4.1** or later.
If unsure, ask your IT team or search "h2 CVE-2026-71554" on the vendor's site.
CVE-2026-71554 (h2) — CWE-444 / CVSS v3 5.3
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: Host header
Patched: `4.4.1` — apply immediately
Workaround: Users of the h2 library are advised to check and follow HTTP semantics best practices in their application code.
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-444) exists in h2. Attackers reach the vulnerable code path via `Host header` without authentication.
📍 Affected scope
h2 — . Attack surface: Host header.
🔥 Severity
Severity: Medium (CVSS 5.3/10). Risk of unauthorized operations or information disclosure
🔧 How to fix
Update to **4.4.1**.
🛡️ Workaround
Workaround: Users of the h2 library are advised to check and follow HTTP semantics best practices in their application code.
🔍 Detection
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run `grep -r 'h2' .` against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response Actions (7 steps)
Concrete steps and command examples for SOC/SRE teams to execute in order
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1Identify exposure identify
grep -r 'h2' . | 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 `h2` を grep し、稼働しているサービス・バージョンを把握する。
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5Apply temporary workaround mitigate
Users of the h2 library are advised to check and follow HTTP semantics best practices in their application code.パッチが適用されるまでの応急処置として、Users of the h2 library are advised to check and follow HTTP semantics best practices in their application code. を実施。回避策の副作用 (機能低下) を確認した上で。
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6Apply patch patch
Upgrade h2 to 4.4.1ステージング環境で 4.4.1 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と、Step 3 で見つけた異常検知の続報チェックを含めること。
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7Post-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 Step 3 と同じログクエリでアラート再発が無いか継続監視。
Affected packages
pip
h2
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"4.4.1"}]}]