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CVE-2026-9679 medium CVSS 5.9

Vulnerability in undici (CVE-2026-9679)

Summary

vulnerability in undici (CVE-2026-9679). Data can be tampered with by attackers. Exploitable via ``parseSetCookie``. Mitigation: upgrade to `8.5.0` or later.

AI summary snake-internal / snake-material-v2

A vulnerability tracked as **CVE-2026-9679** has been found in undici. Attackers can target a specific entry point like ``parseSetCookie`` over the network to misuse the product. Data can be tampered with by attackers. CVSS score: 5.9/10. What to do: upgrade undici to **8.5.0** or later. If unsure, ask your IT team or search "undici CVE-2026-9679" on the vendor's site.
CVE-2026-9679 (undici) — CWE-93 / CVSS v3 5.9 Attack vector: remote (network-reachable) / unauthenticated / no user interaction Attack surface: `parseSetCookie` / `qsUnescape` / `Location` / `parseCookie` Patched: `8.5.0` — apply immediately Workaround: If upgrade is not immediately possible, do not forward values returned by `parseSetCookie`/`parseCookie`/`getSetCookies` directly into response headers; sanitize the value first to strip or reject CR, LF, NUL, `;`, and `=` bytes. 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-93) exists in undici. Attackers reach the vulnerable code path via ``parseSetCookie`` without authentication.
📍 Affected scope
undici — . Attack surface: `parseSetCookie` / `qsUnescape` / `Location` / `parseCookie`.
🔥 Severity
Severity: Medium (CVSS 5.9/10). Data can be tampered with by attackers
🔧 How to fix
Update to **8.5.0**.
🛡️ Workaround
Workaround: If upgrade is not immediately possible, do not forward values returned by `parseSetCookie`/`parseCookie`/`getSetCookies` directly into response headers; sanitize the value first to strip or reject CR, LF, NUL, `;`, and `=` bytes.
🔍 Detection
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run `grep -r 'undici' .` 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

  1. 1
    Identify exposure identify 
    grep -r 'undici' . | 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 `undici` を grep し、稼働しているサービス・バージョンを把握する。

  2. 5
    Apply temporary workaround mitigate 
    If upgrade is not immediately possible, do not forward values returned by `parseSetCookie`/`parseCookie`/`getSetCookies` directly into response headers; sanitize the value first to strip or reject CR, LF, NUL, `;`, and `=` bytes.

    パッチが適用されるまでの応急処置として、If upgrade is not immediately possible, do not forward values returned by `parseSetCookie`/`parseCookie`/`getSetCookies` directly into response headers; sanitize the value first to strip or reject CR, LF, NUL, `;`, and `=` bytes. を実施。回避策の副作用 (機能低下) を確認した上で。

  3. 6
    Apply patch patch 
    Upgrade undici to 8.5.0

    ステージング環境で 8.5.0 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。

  4. 7
    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 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

npm undici
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"8.5.0"}]}]

References

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