high · 7.5 Patched

undici vulnerable to Denial of Service via unhandled error on excessive content-encodings

CVE-2026-109869 · GHSA-xjj6-f33q-929c · published 23 Oct 2026

How serious is it

  • Severity: high, CVSS score 7.5 out of 10.
  • No exploit prediction (EPSS) score yet.
  • Not on the CISA list of exploited vulnerabilities.
  • No public exploit in Exploit-DB.

Is your app affected by CVE-2026-109869?

Paste this prompt into Claude Code, Cursor or any AI coding tool: it runs a free Shippable scan of your project and fixes what it finds. Built with Lovable, Bolt or v0? Scan your live app. Or upload your package file.

Who is affected

  • undici (npm) >= 6.23.0, < 6.29.1
  • undici (npm) >= 7.18.0, < 7.30.1
  • undici (npm) >= 8.0.0, < 8.12.2

How to check

  1. Run npm ls undici in your project to see the installed version, including copies pulled in by other packages.
  2. Or paste your lockfile into the checker: it lists every package with a known vulnerability, this one included.
  3. Or run npx shippable-dev scan localhost:3000 in your project folder. It reads your lockfile and flags this vulnerability along with every other known one.

How to fix

Copies a prompt for Claude Code, Cursor or Codex: it checks your lockfiles for this and upgrades it.
  1. On >= 6.23.0, < 6.29.1: Upgrade undici to 6.29.1 or later, commit the lockfile and redeploy.
  2. On >= 7.18.0, < 7.30.1: Upgrade undici to 7.30.1 or later, commit the lockfile and redeploy.
  3. On >= 8.0.0, < 8.12.2: Upgrade undici to 8.12.2 or later, commit the lockfile and redeploy.
  4. If a vulnerable version was live, check your logs and rotate the secrets that server could read.

The advisory

### Impact undici's `fetch()` crashes the Node.js process when a malicious server returns a response with more than five content codings and closes the connection before sending the body. undici rejects such responses (a content-encoding limit), but it created the internal response stream before that check and returned without attaching an error listener or aborting the request. The early close then surfaces a content-length mismatch on that orphaned internal stream, which Node.js treats as an unhandled `error` and terminates the process. A remote, unauthenticated server can trigger this with a single response, even when the application correctly catches the `fetch()` rejection. undici 6.x, 7.x, and 8.x are affected. ### Patches Upgrade to `6.29.1`, `7.30.1`, or `8.12.2`. undici now validates the content-encoding chain before creating the internal body stream and aborts the response when the limit is exceeded, so no error can surface on an orphaned stream. ### Workarounds None.

Check your whole app

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References

Merged from GitHub Advisory Database, OSV. Last updated 26 Oct 2026. All vulnerabilities · RSS · JSON

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