How severe is CVE-2026-6733?

CVE-2026-6733 has a CVSS score of 3.7/10, rated LOW. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2026-6733?

CVE-2026-6733 affects the following packages: undici (npm), undici (npm), undici (npm). Ecosystems affected: npm.

How do I fix CVE-2026-6733?

Update undici to 6.27.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-6733 is resolved across your whole dependency graph.

How do I detect CVE-2026-6733 in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for undici, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-6733 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2026-6733 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-6733 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-6733?

CVE-2026-6733 has an EPSS (Exploit Prediction Scoring System) score of 0.3%, placing it in the 17th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-6733?

CVE-2026-6733 is classified as CWE-367 (CWE-367). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-6733 published, and has it been updated?

CVE-2026-6733 was published on June 17, 2026 and was last updated on September 29, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦

📦 npm

Not in CISA KEV

LOW severity

CVE-2026-6733 — undici

LOWFix: nodejs/undici@6ea54ef

CVE-2026-6733 is a low-severity (CVSS 3.7) CWE-367 vulnerability in undici. A fix is available for undici — see the affected versions and patch details below.

undici vulnerable to HTTP response queue poisoning via keep-alive socket reuse

Also known asGHSA-35p6-xmwp-9g52

Published

Jun 17, 2026

Updated

Sep 29, 2026

Affected

3 pkgs

Patched

3 / 3

Exploits

None indexed

Exploitation data as of Oct 5, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-6733.

EPSS Exploitation Probability

via FIRST.org ↗

0.3%probability of exploitation in next 30 days

Lower Risk+0.05%

Lower risk than most CVEs17th percentile — riskier than 17% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2026-6733 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 383,485 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

3 pkgs affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

8Kother npm packages depend on this — each one inherits the vulnerability until it's patched upstream

undicinpm

247.7Mdownloads / week

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 v6.27.0, v7.28.0 or v8.5.0.

Workarounds

Disable keep-alive connection reuse by setting keepAliveTimeout: 0 on the Client or Pool.

Affected Packages

3 total 3 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`undici`	all versions	6.27.0`npm install undici@6.27.0`
📦npm	`undici`	≥ 7.0.0&&< 7.28.0	7.28.0`npm install undici@7.28.0`
📦npm	`undici`	≥ 8.0.0&&< 8.5.0	8.5.0`npm install undici@8.5.0`

Affected Products

1 product · 3 configurations

Application

undicinodejs

≥ 8.0.0 && < 8.5.0

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for undici, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update undici to 6.27.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-6733 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatLow

Low: A flaw in Undici's HTTP/1.1 client, as used in various Red Hat products, allows an attacker-controlled upstream server to inject unsolicited responses onto reused keep-alive sockets. This can lead to incorrect response delivery, potentially impacting data integrity, but requires a compromised server and active…

Workaround published by Red Hat

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.

Source: Red Hat security advisory for CVE-2026-6733 (CC BY 4.0)

Product	Fixed in	Advisory
Red Hat Enterprise Linux 10	`nodejs24-1:24.18.0-1.el10_2`	RHSA-2026:35841
Red Hat Enterprise Linux 10	`nodejs22-1:22.23.1-2.el10_2`	RHSA-2026:35842
Red Hat Enterprise Linux 8	`nodejs:24-8100020260630152626.6d880403`	RHSA-2026:39868
Red Hat Enterprise Linux 8	`nodejs:22-8100020260703140402.6d880403`	RHSA-2026:41947
Red Hat Enterprise Linux 9	`nodejs:24-9080020260626074955.rhel9`	RHSA-2026:35891
Red Hat Enterprise Linux 9	`nodejs:22-9080020260626075442.rhel9`	RHSA-2026:35892
Red Hat Hardened Images	`nodejs26-main-26.5.0-1.3.hum1`	RHSA-2026:38009
Red Hat Hardened Images	`nodejs24-main-24.18.0-0.3.hum1`	RHSA-2026:38236

Frequently Asked Questions

## 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 v6.27.0, v7.28.0 or v8.5.0. ## Workarounds