undici WebSocket client vulnerable to Denial of Service via unbounded automatic PONG buffering

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2026-109932: 0.32% estimated exploitation activity in the next 30 days; percentile 25.16 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact undici's WebSocket client (including Node.js's bundled `globalThis.WebSocket`) can be driven to exhaust process memory by a malicious or compromised WebSocket server. For every PING frame received, the receiver automatically writes a PONG response to the socket and ignores the `false` return value from `socket.write()`, which is a backpressure signal, so a server that streams small PING frames while never reading the client's PONGs makes the outbound write queue and heap grow without bound until the Node.js process runs out of memory and terminates. The attack is remote and unauthenticated, needs only a normal WebSocket connection, and is asymmetric: small inbound PINGs produce a much larger retained outbound queue. Availability is the only impact. undici 5.x, 6.x, 7.x, and 8.x are affected; the WebSocket client was introduced in 5.15.0.

Patches Upgrade to `6.29.1`, `7.30.1`, or `8.12.2`, which pause WebSocket frame parsing when the automatic PONG response hits socket…

Published by the source

27 Oct 2026, 19:02 UTC

Last modified by the source

27 Oct 2026, 19:15 UTC

Source last checked

28 Oct 2026, 06:00 UTC

1. Revision 2 · amended · 28 Oct 2026

   Amended from osv record GHSA-9fm3-97px-rjf6

2. Revision 1 · created · 27 Oct 2026

   Published from ghsa record GHSA-9fm3-97px-rjf6

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# Patch Next advisory brief: CVE-2026-109932

Advisory: undici WebSocket client vulnerable to Denial of Service via unbounded automatic PONG buffering
IDs: CVE-2026-109932, GHSA-9fm3-97px-rjf6
Record: https://patchnext.com/advisories/cve-2026-109932 (revision 2, source checked 28 Oct 2026, 06:00 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: undici 8.12.2, 7.30.1, 6.29.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm undici: affected >= 5.15.0, < 6.29.1; >= 7.0.0, < 7.30.1; >= 8.0.0, < 8.12.2; fixed in 8.12.2, 6.29.1, 7.30.1

## Suggested inspection (read-only)
- `npm ls undici --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on undici.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-9fm3-97px-rjf6 (GitHub-reviewed advisory GHSA-9fm3-97px-rjf6 lists affected ranges: npm undici >=5.15.0 =7.0.0 =8.0.0 <8.12.2)
- Verified: https://osv.dev/vulnerability/GHSA-9fm3-97px-rjf6 (OSV record GHSA-9fm3-97px-rjf6 lists affected ranges: npm undici >=5.15.0 =7.0.0 =8.0.0 <8.12.2 (fixed))

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