How severe is CVE-2026-12151?

CVE-2026-12151 has a CVSS score of 7.5/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2026-12151?

CVE-2026-12151 affects the following packages: undici (npm), undici (npm), undici (npm). Ecosystems affected: npm.

How do I fix CVE-2026-12151?

Update undici to 6.27.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-12151 is resolved across your whole dependency graph.

How do I detect CVE-2026-12151 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-2026-12151 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-2026-12151 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-12151 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-2026-12151?

CVE-2026-12151 has an EPSS (Exploit Prediction Scoring System) score of 0.8%, placing it in the 54th 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-2026-12151?

CVE-2026-12151 is classified as Uncontrolled Resource Consumption (CWE-400), CWE-770 (CWE-770). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-12151 published, and has it been updated?

CVE-2026-12151 was published on June 17, 2026 and was last updated on September 18, 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-2026-12151 — undici

HIGH

CVE-2026-12151 is a high-severity (CVSS 7.5) Uncontrolled Resource Consumption vulnerability in undici. A fix is available for undici — see the affected versions and patch details below.

undici WebSocket client vulnerable to denial of service via fragment count bypass

Also known asGHSA-vxpw-j846-p89q

Published

Jun 17, 2026

Updated

Sep 18, 2026

Affected

3 pkgs

Patched

3 / 3

Exploits

None indexed

Exploitation data as of Sep 26, 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-2026-12151.

EPSS Exploitation Probability

via FIRST.org ↗

0.8%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs54th percentile — riskier than 54% of all scored CVEsHighest risk

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

How urgent is this, really

CVE-2026-12151 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 379,842 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

211.9Mdownloads / week

Description

Impact: The undici WebSocket client enforces maxPayloadSize on the cumulative byte count of fragments in a message but does not enforce a limit on the number of fragments. A malicious WebSocket server can stream many small or empty continuation frames that each pass per-frame and cumulative-size validation, collectively causing unbounded memory growth in the client process. The result is memory exhaustion and a denial of service.

Affected applications are those using the undici WebSocket client (new WebSocket(...)) or the WebSocketStream API that can be induced to connect to an attacker-controlled or compromised WebSocket endpoint.

All releases starting at undici 6.17.0 are affected.

Patches: Upgrade to undici >= 6.26.0, >= 7.28.0, or >= 8.5.0. Workarounds: No workaround is available. The fix must be applied through an upgrade.

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-2026-12151 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

This Important denial of service flaw in the `undici` WebSocket client allows a remote attacker to cause unbounded memory growth. By sending numerous small or empty WebSocket frames, an unauthenticated attacker can exhaust system memory, leading to a denial of service in Red Hat products that use the affected client.

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-2026-12151 (CC BY 4.0)

Product	Fixed in	Advisory
Cryostat 4 on RHEL 9	`cryostat/cryostat-grafana-dashboard-rhel9:4.2.0-13`	RHSA-2026:48151
Red Hat AMQ Broker 7.13.6	`undici`	RHSA-2026:66545
Red Hat AMQ Broker 7.14.1	`undici`	RHSA-2026:66488
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 10.0 Extended Update Support	`nodejs22-1:22.23.1-2.el10_0`	RHSA-2026:39246
Red Hat Enterprise Linux 8	`nodejs:24-8100020260630152626.6d880403`	RHSA-2026:39868
Red Hat Enterprise Linux 8	`nodejs:22-8100020260703140402.6d880403`	RHSA-2026:41947

Frequently Asked Questions

O3 Security · Impact-Aware SCA

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