# 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.

- **Severity:** Low 3.7 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 17 Jun 2026
- **Updated:** 17 Jun 2026
- **Also known as:** CLEANSTART-2026-BS54075, CLEANSTART-2026-UR64263, CLSA-2026-1784112338, CLSA-2026-1784113246, CLSA-2026-1791631203, DEBIAN-CVE-2026-6733, ECHO-0ed3-95c6-1c1c, GHSA-35p6-xmwp-9g52, MINI-2rwr-3p5f-xwv2, MINI-2x9c-w27j-9f9j, MINI-48mp-hcph-jc47, MINI-5q2j-2pc8-fqv4, MINI-83vf-6w2f-5mm2, MINI-8vfr-4j26-85wq, MINI-f7rc-cv66-j79j, MINI-f9jh-35qf-cc6x, MINI-g2qc-v948-5xm4, MINI-m77v-6x22-pq5p, MINI-pjw6-9ff5-qp97, MINI-r6j2-8vqf-phrp, MINI-v647-4rr9-344c, MINI-vjw5-c748-8wr3, MINI-w6vg-jgm9-m4h6, MINI-wgq4-mcvh-fhhf, ROOT-APP-NPM-CVE-2026-6733, UBUNTU-CVE-2026-6733

## 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 (Time-of-check Time-of-use (TOCTOU) Race Condition)

## Which versions are affected by CVE-2026-6733?

6 open source packages ship an affected version, including undici. It affects 1 product.


| Package | Ecosystem | 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: 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](https://insights.sbomify.com/CVE-2026-109855/): undici WebSocket client vulnerable to Denial of Service via failed HTTP/2 handshake (high 7.5)
- [CVE-2026-109869](https://insights.sbomify.com/CVE-2026-109869/): undici vulnerable to Denial of Service via unhandled error on excessive content-encodings (high 7.5)
- [CVE-2026-87018](https://insights.sbomify.com/CVE-2026-87018/): undici vulnerable to Denial of Service via TLS 1.2 certificate-changing renegotiation (high 7.5)
- [CVE-2026-19534](https://insights.sbomify.com/CVE-2026-19534/): undici vulnerable to Denial of Service via unrequested WebSocket subprotocol (high 7.5)
- [CVE-2026-12151](https://insights.sbomify.com/CVE-2026-12151/): undici WebSocket client vulnerable to denial of service via fragment count bypass (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-6733 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-6733 in the wild and no public exploit code.

Affected packages and fixed versions:
- undici (npm): affected all versions; fixed in 6.27.0
- undici (npm): affected all versions; fixed in 6.27.0
- undici (npm): affected from 7.0.0; fixed in 7.28.0
- undici (npm): affected from 7.0.0; fixed in 7.28.0
- undici (npm): affected from 8.0.0; fixed in 8.5.0
- undici (npm): affected from 8.0.0; fixed in 8.5.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-6733/ (Markdown: https://insights.sbomify.com/CVE-2026-6733/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-6733
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-6733
- OSV: https://osv.dev/vulnerability/CVE-2026-6733

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-6733/
Summaries are generated and may contain mistakes; the official description above is the record.