high · 7.4 Patched

undici vulnerable to cache poisoning and cross-user disclosure via cross-origin redirects

CVE-2026-109829 · GHSA-4w7w-5xrc-9h26 · published 27 Oct 2026

How serious is it

  • Severity: high, CVSS score 7.4 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-2026-109829?

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) >= 7.0.0, < 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 >= 7.0.0, < 7.30.1: Upgrade undici to 7.30.1 or later, commit the lockfile and redeploy.
  2. On >= 8.0.0, < 8.12.2: Upgrade undici to 8.12.2 or later, commit the lockfile and redeploy.
  3. If a vulnerable version was live, check your logs and rotate the secrets that server could read.

The advisory

### Impact When an originless `Agent` composes the redirect and cache interceptors as `compose(redirect(), cache())` with a shared cache (`type: 'shared'`), the cache builds its key from the original request URL before the redirect handler changes the origin. The response produced after a redirect is then stored under the original key, even when the redirect crossed to a different origin. An attacker who controls the target of a redirect from a trusted URL can have their response cached under that trusted URL. A later caller requesting the trusted URL receives the attacker's body from the shared cache without either origin being contacted, allowing persistent cache poisoning. The same key confusion also discloses private data: when an authenticated request returns a `private, no-store` redirect to a user-specific resource, the final response is stored under the original URL and can be served to a later unauthenticated caller. The cache interceptor was introduced in undici 7.0.0, and all 7.x and 8.x releases before the patched versions are affected. Applications are affected only when an originless `Agent`, a shared `MemoryCacheStore` or `SqliteCacheStore`, and the composition `compose(redirect(), cache())` are all used. Origin-bound `Client` and `Pool` dispatchers, and the reverse composition `compose(cache(), redirect())`, are not affected. ### Patches Upgrade to `7.30.1` or `8.12.2`. Before storing a response, undici now verifies that the origin that produced it still matches the cache key, and preserves each redirect hop's cache-control policy, so cross-origin redirect responses and responses behind a `no-store` or `private` hop are no longer cached under the original key. ### Workarounds Compose the interceptors as `compose(cache(), redirect())`, use per-origin dispatchers and cache stores, or disable shared caching on redirect-capable requests.

Check your whole app

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References

Merged from GitHub Advisory Database, OSV. Last updated 28 Oct 2026. All vulnerabilities · RSS · JSON