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CVE-2026-16729 medium CVSS 4.8

Vulnerability in undici (CVE-2026-16729)

Summary

Vulnerability in undici (CVE-2026-16729). Risk of unauthorized operations or information disclosure. Exploitable via setCookie. Mitigation: upgrade to 8.9.0 or later.

Original description

The description as published by the source.

Impact

The setCookie function has two attribute injection paths. validateCookieDomain does not reject semicolons (validateCookiePath already does at 0x3B), so a domain value like example.com; SameSite=None lands verbatim as Domain=example.com; SameSite=None. The unparsed array's loop only checks each entry contains = and does not sanitize values, so an entry like X-Custom=val; HttpOnly lands unchanged, injecting HttpOnly without the caller setting cookie.httpOnly = true.

Applications that pass user-controlled input to these fields, typically multi-tenant or reverse-proxy servers that scope session cookies to a tenant-supplied domain, can have SameSite CSRF protections bypassed, Secure or HttpOnly forced or stripped, or the intended SameSite tier overridden.

Patches

Patched in undici v6.28.0, v7.29.0, and v8.9.0.

Workarounds

  • Sanitize domain values against the RFC 1034 letter-digit-hyphen set before passing to setCookie.
  • Do not pass user-controlled data to the unparsed field.

Source: NIST National Vulnerability Database NVD GitHub Advisory

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-2026-16729 has been found in undici.
Attackers can target a specific entry point like setCookie over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 4.8/10.
What to do: upgrade undici to 8.9.0 or later.
If unsure, ask your IT team or search "undici CVE-2026-16729" on the vendor's site.

CVE-2026-16729 (undici) — CWE-74 / CVSS v3 4.8
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: setCookie / validateCookieDomain / validateCookiePath / domain
Patched: 8.9.0 — 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-74) exists in undici. Attackers reach the vulnerable code path via setCookie without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of undici. Attack surface: setCookie / validateCookieDomain / validateCookiePath / domain.

🔥 Severity

Severity: Medium (CVSS 4.8/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 8.9.0.

🛡️ 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 'undici' . 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 '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. 2
    Apply patch patch 
    Upgrade undici to 8.9.0

    ステージング環境で 8.9.0 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

npm undici
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"8.9.0"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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