CVE-2026-84933 undici vulnerable to cross-user cookie disclosure via Set-Cookie caching in shared caches
undici's shared cache leaks Set-Cookie headers to other users, allowing cookie disclosure and injection by untrusted servers.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-84933?
CVE-2026-84933 is a medium-severity vulnerability in Nodejs Undici, published on 4 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
undici's cache interceptor does not handle the Set-Cookie response header anywhere in its cache path, so it neither refuses to store nor strips that header. In shared cache mode, which is the default, an otherwise cacheable response that carries a Set-Cookie header, for example one marked with a public and max-age directive, is stored and then re-served to a later caller that matches the same cache key. As a result one caller's cookie is disclosed to a different caller, and an untrusted server can inject cookies into cached responses served to all subsequent callers. This violates the requirement that a shared cache must not store cookies. This affects undici versions from 7.0.0 up to 7.29.1 and from 8.0.0 up to 8.10.2. Users should upgrade to undici 7.29.1 or 8.10.2.
Which versions are affected by CVE-2026-84933?
4 open source packages ship an affected version, including undici. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
undici npm | From 7.0.0 | 7.29.1 |
undici npm | From 7.0.0 | 7.29.1 |
undici npm | From 8.0.0 | 8.10.2 |
undici npm | From 8.0.0 | 8.10.2 |
Products include Nodejs Undici.
How do I fix CVE-2026-84933?
Upgrade undici to a fixed version for your release line: 7.29.1 or 8.10.2.
Is CVE-2026-84933 being exploited?
There is no known exploitation of CVE-2026-84933 in the wild and no public exploit code.
Other vulnerabilities in Nodejs Undici
- CVE-2026-109855 undici WebSocket client vulnerable to Denial of Service via failed HTTP/2 handshake
- CVE-2026-109869 undici vulnerable to Denial of Service via unhandled error on excessive content-encodings
- CVE-2026-87018 undici vulnerable to Denial of Service via TLS 1.2 certificate-changing renegotiation
- CVE-2026-19534 undici vulnerable to Denial of Service via unrequested WebSocket subprotocol
- CVE-2026-12151 undici WebSocket client vulnerable to denial of service via fragment count bypass
Sources
Also known as CLEANSTART-2026-HS02762, CLEANSTART-2026-VO74481, CLEANSTART-2026-WF83239, CLEANSTART-2026-XL00241, CLSA-2026-1790756976, CLSA-2026-1790863452 and 22 more.