undici vulnerable to Denial of Service via unbounded memory in the EventSource parser

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-2026-109924: 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 EventSource client can be driven to exhaust process memory by a malicious or compromised Server-Sent Events peer. By sending millions of tiny completed data: fields with no blank event separator, or a single unfinished line split across many chunks, the parser retains a growing amount of per-field and per-chunk state. The byte-based maxEventSize and maxResponseSize limits do not bound that retained state, and maxResponseSize is enforced on the compressed body before decompression, so a small compressed response can expand into enough retained memory to terminate the process. The application only needs to maintain an EventSource connection to an untrusted peer, which controls only the response. Availability is the only impact. Patches Upgrade to 6.29.1, 7.30.1, or 8.12.2, which bound the retained EventSource parser state (the number of data fields and buffered chunks, the unfinished-line length, and per-field byte totals) independently of the byte limits. Workarounds…

Published by the source

23 Oct 2026, 22:13 UTC

Last modified by the source

23 Oct 2026, 22:30 UTC

Source last checked

26 Oct 2026, 13:07 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-4qv8-2p9j-2685

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-4qv8-2p9j-2685

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-4qv8-2p9j-2685

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# Patch Next advisory brief: CVE-2026-109924

Advisory: undici vulnerable to Denial of Service via unbounded memory in the EventSource parser
IDs: CVE-2026-109924, GHSA-4qv8-2p9j-2685
Record: https://patchnext.com/advisories/cve-2026-109924 (revision 3, source checked 26 Oct 2026, 13:07 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 >= 6.5.0, < 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-4qv8-2p9j-2685 (GitHub-reviewed advisory GHSA-4qv8-2p9j-2685 lists affected ranges: npm undici >=6.5.0 =7.0.0 =8.0.0 <8.12.2)
- Verified: https://osv.dev/vulnerability/GHSA-4qv8-2p9j-2685 (OSV record GHSA-4qv8-2p9j-2685 lists affected ranges: npm undici >=6.5.0 =7.0.0 =8.0.0 <8.12.2 (fixed))

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