CVE-2026-6733 undici vulnerable to HTTP response queue poisoning via keep-alive socket reuse
An attacker-controlled server can poison HTTP response queues in undici, causing responses to be delivered to wrong requests via keep-alive reuse.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-6733?
CVE-2026-6733 is a low-severity vulnerability in Nodejs Undici, published on 17 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Impact: Undici's HTTP/1.1 client is vulnerable to response queue poisoning on reused keep-alive sockets. An attacker-controlled upstream server can inject an unsolicited HTTP/1.1 response onto an idle socket after a request completes. When the client dispatches the next request on that socket, it associates the injected response with the new request, causing responses to be delivered to the wrong requests.
This requires an attacker-controlled or compromised upstream HTTP/1.1 server and keep-alive connection reuse.
Patches: Upgrade to undici v6.26.0, v7.28.0 or v8.5.0.
Workarounds: Disable keep-alive connection reuse by setting keepAliveTimeout: 0 on the Client or Pool.
Weakness: CWE-367
Which versions are affected by CVE-2026-6733?
6 open source packages ship an affected version, including undici. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
undici npm | All versions | 6.27.0 |
undici npm | All versions | 6.27.0 |
undici npm | From 7.0.0 | 7.28.0 |
undici npm | From 7.0.0 | 7.28.0 |
undici npm | From 8.0.0 | 8.5.0 |
undici npm | From 8.0.0 | 8.5.0 |
Products include Nodejs Undici.
How do I fix CVE-2026-6733?
Upgrade undici to a fixed version for your release line: 6.27.0, 7.28.0 or 8.5.0.
Is CVE-2026-6733 being exploited?
There is no known exploitation of CVE-2026-6733 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-BS54075, CLEANSTART-2026-UR64263, CLSA-2026-1784112338, CLSA-2026-1784113246, CLSA-2026-1791631203, DEBIAN-CVE-2026-6733 and 20 more.