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CVE-2026-16728 medium CVSS 4.8

Vulnerability in undici (CVE-2026-16728)

Summary

Vulnerability in undici (CVE-2026-16728). Risk of unauthorized operations or information disclosure. Mitigation: upgrade to 8.9.0 or later.

Original description

The description as published by the source.

Impact

Undici's interceptors.retry() can deliver a response whose body length does not match the Content-Length header exposed to the application after a retry or resume of a partial response. Applications that use interceptors.retry() and forward upstream response headers and bodies downstream, for example proxy or gateway applications, may emit an invalid HTTP response with a stale Content-Length header. This can lead to downstream response desynchronization, connection hangs, or response corruption in clients or intermediaries that rely on the forwarded framing metadata.

A malicious or faulty upstream can respond to a range request with a 206 Partial Content response such as:

Content-Range: bytes 0-99/300
Content-Length: 300

and then send only 99 bytes before closing the socket. interceptors.retry() can then retry with Range: bytes=99-99, receive the final byte, and deliver a 100-byte body to the application while the response headers still contain Content-Length: 300 from the first response.

The bug requires interceptors.retry() to be enabled, an upstream that returns a partial response with a mismatched framing header, and a downstream forwarder that does not remove or recalculate Content-Length.

Patches

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

Workarounds

  • Disable interceptors.retry() for untrusted upstreams.
  • Remove or recalculate Content-Length bef…

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-2026-16728 has been found in undici.
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-2026-16728" on the vendor's site.

CVE-2026-16728 (undici) — CWE-444 / CVSS v3 4.8
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
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-444) exists in undici.

📍 Affected scope

Check the vendor advisory for the affected versions of undici.

🔥 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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