KEVWire

Security intelligence, with context.

Response snapshot Nov 4, 2026, 04:56 UTC

Back to the wire
Permalink
VulnerabilityCVE-2026-12151

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

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.

At a glance

Exploited
Not known
Severity
7.5 High (CVSS 3.1)
Chance of exploitation
Not estimated
Sources
1 source

What to do

GitHub lists first patched versions: undici: 6.27.0; undici: 7.28.0; undici: 8.5.0. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-vxpw-j846-p89q (opens a new tab)

What happened

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.

Continue reading

Patches

Upgrade to undici v6.27.0, v7.28.0 or v8.5.0.

Workarounds

No workaround is available. The fix must be applied through an upgrade.

Affected package ranges reported by GitHub: undici: < 6.27.0 undici: >= 7.0.0, < 7.28.0 undici: >= 8.0.0, < 8.5.0

Scores and how they were measured

CVSS base severity

7.5

Version 3.1As of

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

Not available

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-vxpw-j846-p89q (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-vxpw-j846-p89q, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, November 4). undici WebSocket client vulnerable to denial of service via fragment count bypass (CVE-2026-12151). https://kevwire.com/record/CVE-2026-12151

MLA

"undici WebSocket client vulnerable to denial of service via fragment count bypass (CVE-2026-12151)." KEVWire, 4 Nov. 2026, kevwire.com/record/CVE-2026-12151.

Chicago

KEVWire. "undici WebSocket client vulnerable to denial of service via fragment count bypass (CVE-2026-12151)." Last modified November 4, 2026. https://kevwire.com/record/CVE-2026-12151.

Evidence summary (plain text)

undici WebSocket client vulnerable to denial of service via fragment count bypass (Jun 19, 2026).
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.
CVSS 7.5 (version 3.1; evidence as of Nov 4, 2026; https://github.com/advisories/GHSA-vxpw-j846-p89q).
Sources:
GitHub-reviewed advisory GHSA-vxpw-j846-p89q: https://github.com/advisories/GHSA-vxpw-j846-p89q
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
Record ID: CVE-2026-12151.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Nov 4, 2026, 04:55 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

Record JSON

Your account

Email alerts

Email alerts are coming as part of KEVWire Premium: join the waitlist. To follow your stack today, use its RSS feed, which honors your filters, or connect an AI agent through the API.

Suggest an improvement

Ideas, missing sources, corrections, and bugs are all welcome. No account needed. Suggestions are reviewed by a person before anything changes.

Record details

Record detail