How severe is CVE-2026-2229?

CVE-2026-2229 has a CVSS score of 7.5/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2026-2229?

CVE-2026-2229 affects the following packages: undici (npm), undici (npm). Ecosystems affected: npm.

How do I fix CVE-2026-2229?

Update undici to 6.24.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-2229 is resolved across your whole dependency graph.

How do I detect CVE-2026-2229 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-2026-2229 if there is no patch (or I can't update yet)?

Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Is CVE-2026-2229 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-2229 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-2026-2229?

CVE-2026-2229 has an EPSS (Exploit Prediction Scoring System) score of 0.9%, placing it in the 60th 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-2026-2229?

CVE-2026-2229 is classified as CWE-248 (CWE-248), CWE-1284 (CWE-1284). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-2229 published, and has it been updated?

CVE-2026-2229 was published on March 12, 2026 and was last updated on October 28, 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

HIGH severity

CVE-2026-2229 — undici

HIGH

CVE-2026-2229 is a high-severity (CVSS 7.5) CWE-248 vulnerability in undici. A fix is available for undici — see the affected versions and patch details below.

undici is vulnerable to Unhandled Exception in undici WebSocket Client Due to Invalid server_max_window_bits Validation

Also known asGHSA-v9p9-hfj2-hcw8

Published

Mar 12, 2026

Updated

Oct 28, 2026

Affected

2 pkgs

Patched

2 / 2

Exploits

None indexed

Exploitation data as of Nov 4, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
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-2026-2229.

EPSS Exploitation Probability

via FIRST.org ↗

0.9%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs60th percentile — riskier than 60% of all scored CVEsHighest risk

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

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

2 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.

9Kother npm packages depend on this — each one inherits the vulnerability until it's patched upstream

undicinpm

316.1Mdownloads / week

Description

Impact

The undici WebSocket client is vulnerable to a denial-of-service attack due to improper validation of the server_max_window_bits parameter in the permessage-deflate extension. When a WebSocket client connects to a server, it automatically advertises support for permessage-deflate compression. A malicious server can respond with an out-of-range server_max_window_bits value (outside zlib's valid range of 8-15). When the server subsequently sends a compressed frame, the client attempts to create a zlib InflateRaw instance with the invalid windowBits value, causing a synchronous RangeError exception that is not caught, resulting in immediate process termination.

The vulnerability exists because:

The isValidClientWindowBits() function only validates that the value contains ASCII digits, not that it falls within the valid range 8-15
The createInflateRaw() call is not wrapped in a try-catch block
The resulting exception propagates up through the call stack and crashes the Node.js process

Patches

Has the problem been patched? What versions should users upgrade to?

Workarounds

Is there a way for users to fix or remediate the vulnerability without upgrading?

Affected Packages

2 total 2 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`undici`	all versions	6.24.0`npm install undici@6.24.0`
📦npm	`undici`	≥ 7.0.0&&< 7.24.0	7.24.0`npm install undici@7.24.0`

Affected Products

1 product · 2 configurations

Application

undicinodejs

≥ 7.0.0 && < 7.24.0

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 6.24.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-2229 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

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 HatImportant

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-2026-2229 (CC BY 4.0)

Product	Fixed in	Advisory
Cryostat 4 on RHEL 9	`cryostat/cryostat-openshift-console-plugin-rhel9:4.2.0-9`	RHSA-2026:17789
Red Hat Enterprise Linux 10	`nodejs22-1:22.22.2-1.el10_1`	RHSA-2026:7080
Red Hat Enterprise Linux 10	`nodejs24-1:24.14.1-2.el10_1`	RHSA-2026:7675
Red Hat Enterprise Linux 10.0 Extended Update Support	`nodejs22-1:22.22.2-2.el10_0`	RHSA-2026:7310
Red Hat Enterprise Linux 8	`nodejs:22-8100020260331102257.6d880403`	RHSA-2026:7123
Red Hat Enterprise Linux 8	`nodejs:24-8100020260408131901.6d880403`	RHSA-2026:7670
Red Hat Enterprise Linux 9	`nodejs:22-9070020260401095228.rhel9`	RHSA-2026:7302
Red Hat Enterprise Linux 9	`nodejs:24-9070020260402152654.rhel9`	RHSA-2026:7350

Frequently Asked Questions

### Impact The undici WebSocket client is vulnerable to a denial-of-service attack due to improper validation of the `server_max_window_bits` parameter in the permessage-deflate extension. When a WebSocket client connects to a server, it automatically advertises support for permessage-deflate compression. A malicious server can respond with an out-of-range `server_max_window_bits` value (outside zlib's valid range of 8-15). When the server subsequently sends a compressed frame, the client attempts to create a zlib InflateRaw instance with the invalid windowBits value, causing a synchronous Ra

O3 Security · Impact-Aware SCA

Is CVE-2026-2229 in your dependencies?

Find it across npm, including transitive dependencies.

Scan my dependencies How O3 SCA works