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CVE-2026-11525 low CVSS 3.7

Vulnerability in undici (CVE-2026-11525)

Summary

Vulnerability in undici (CVE-2026-11525). Risk of unauthorized operations or information disclosure. Exploitable via SameSite. Mitigation: upgrade to 8.5.0 or later.

Original description

The description as published by the source.

Impact

When undici parses a Set-Cookie header, it accepts any SameSite attribute value that contains Strict, Lax, or None as a substring, rather than the case-insensitive exact match specified by RFC 6265. Non-spec values are silently mapped to one of the three standard tokens:

  • SameSite=NoneOfYourBusiness is parsed as None, the most permissive setting.
  • SameSite=StrictLax is parsed as Lax, a downgrade from Strict.

Affected applications are those that consume Set-Cookie headers from server responses (for example via undici's fetch or proxy code paths) and then forward or rely on the parsed sameSite attribute. A malicious or non-compliant server can coerce the consumer's view of a cookie's SameSite policy to a weaker value, silently degrading the SameSite enforcement the cookie is supposed to provide.

This was introduced in undici 5.15.0 when the cookies feature was added.

Patches

Upgrade to undici v6.27.0, v7.28.0 or v8.5.0.

Workarounds

After parsing a Set-Cookie header, validate that the resulting sameSite attribute is one of 'Strict', 'Lax', or 'None' (exact, case-insensitive) before forwarding or relying on it.

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-2026-11525 has been found in undici.
Attackers can target a specific entry point like SameSite over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 3.7/10.
What to do: upgrade undici to 8.5.0 or later.
If unsure, ask your IT team or search "undici CVE-2026-11525" on the vendor's site.

CVE-2026-11525 (undici) — CWE-183 / CVSS v3 3.7
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: SameSite / Strict / Lax / None
Patched: 8.5.0 — apply immediately
Workaround: After parsing a Set-Cookie header, validate that the resulting sameSite attribute is one of 'Strict', 'Lax', or 'None' (exact, case-insensitive) before forwarding or relying on it.
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-183) exists in undici. Attackers reach the vulnerable code path via SameSite without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of undici. Attack surface: SameSite / Strict / Lax / None.

🔥 Severity

Severity: Low (CVSS 3.7/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 8.5.0.

🛡️ Workaround

Workaround: After parsing a Set-Cookie header, validate that the resulting sameSite attribute is one of 'Strict', 'Lax', or 'None' (exact, case-insensitive) before forwarding or relying on it.

🔍 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 temporary workaround mitigate 
    After parsing a `Set-Cookie` header, validate that the resulting `sameSite` attribute is one of `'Strict'`, `'Lax'`, or `'None'` (exact, case-insensitive) before forwarding or relying on it.

    パッチが適用されるまでの応急処置として、After parsing a Set-Cookie header, validate that the resulting sameSite attribute is one of 'Strict', 'Lax', or 'None' (exact, case-insensitive) before forwarding or relying on it. を実施。回避策の副作用 (機能低下) を確認した上で。

  3. 3
    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を含めること。

  4. 4
    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":"SEMVER","events":[{"introduced":"8.0.0"},{"fixed":"8.5.0"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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