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CVE-2026-15157 medium CVSS 4.2

Vulnerability in undici (CVE-2026-15157)

Summary

Vulnerability in undici (CVE-2026-15157). Risk of unauthorized operations or information disclosure. Exploitable via body.type. Mitigation: upgrade to 6.24.0 or later.

Original description

The description as published by the source.

Impact

When an application passes a duck-typed blob-like body to undici's HTTP/1.1 dispatcher (via request(), stream(), pipeline(), or dispatch()) with a .type derived from untrusted input, an attacker can inject CRLF sequences (\r\n) to append arbitrary HTTP headers and potentially smuggle a second request past the upstream.

The vulnerable branch in lib/dispatcher/client-h1.js pushes body.type directly into the outgoing headers with no validation, while every other header path in undici goes through isValidHeaderValue():

} else if (util.isBlobLike(body) && request.contentType == null && body.type) {
  headers.push('content-type', body.type)  // bypasses isValidHeaderValue()
}

The bug requires a hand-rolled duck-typed blob object or a Blob subclass with a controlled .type. Native Blob is safe because its constructor strips CRLF from .type. fetch() is unaffected because it validates via the Headers class. Ecosystem consumers that build duck-typed blob shapes from user input include form-data-encoder, formdata-polyfill, and formdata-node.

Same defect class as CVE-2022-35948 (explicit content-type sink, fixed in undici 5.8.2) and CVE-2026-1527 (upgrade option sink, fixed in 6.24.0 / 7.24.0), both closed by adding isValidHeaderValue() on their respective sinks. This branch was missed.

Patches

Patched in undici v6.28.0, v7.29.0, and v8.9.0. Users should upgrade to one of these versions or later.

Work…

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-2026-15157 has been found in undici.
Attackers can target a specific entry point like body.type over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 4.2/10.
What to do: upgrade undici to 6.24.0 or later.
If unsure, ask your IT team or search "undici CVE-2026-15157" on the vendor's site.

CVE-2026-15157 (undici) — CWE-93 / CVSS v3 4.2
Attack vector: remote (network-reachable) / unauthenticated
Attack surface: body.type / Blob / Headers / upgrade
Patched: 6.24.0 — 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-93) exists in undici. Attackers reach the vulnerable code path via body.type without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of undici. Attack surface: body.type / Blob / Headers / upgrade.

🔥 Severity

Severity: Medium (CVSS 4.2/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 6.24.0.

🛡️ 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 6.24.0

    ステージング環境で 6.24.0 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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