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Response snapshot Oct 27, 2026, 04:01 UTC

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VulnerabilityCVE-2026-109924

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

undici is an HTTP client library for Node.js. In versions 6.5.0 through 6.29.0, 7.0.0 through 7.30.0, and 8.0.0 through 8.12.1, its EventSource client can be driven to exhaust process memory by a malicious or compromised Server-Sent Events peer.

At a glance

Exploited
Not known
Severity
5.9 Medium (CVSS 3.1)
Chance of exploitation
0.3% in the next 30 days
Sources
3 independent sources

What to do

Check the vendor advisory for affected versions and fixes.

Read NVD CVE-2026-109924 (opens a new tab)

What happened

undici is an HTTP client library for Node.js. In versions 6.5.0 through 6.29.0, 7.0.0 through 7.30.0, and 8.0.0 through 8.12.1, its 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 that the byte-based maxEventSize and maxResponseSize limits do not bound, and because maxResponseSize is enforced on the compressed body before decompression, a small compressed response can expand into enough retained memory to terminate the process.

An application only needs to maintain an EventSource connection to an untrusted peer, which controls only the response, and availability is the only impact. The issue is fixed in undici 6.29.1, 7.30.1, and 8.12.2, which bound the retained parser state independently of the byte limits, and users should upgrade to one of those versions or later. There is no workaround.

Scores and how they were measured

CVSS base severity

5.9

Version 3.1As of

CVSS:3.1/AV:N/AC:H/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

0.3%

Scored Percentile 24.9%

Model and measurement source (opens a new tab)

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

Related technology

Sources

  1. Primary source

    NVD CVE-2026-109924 (opens a new tab)

    NVD record: description, CVSS (the CNA score is preferred), affected products, and publication date. Not evidence of exploitation.

    Published Checked

  2. Primary source

    Vendor advisory (via NVD references) (opens a new tab)

    The vendor advisory referenced by the CVE record, for affected versions and fixes.

    Published Date not suppliedChecked

  3. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  4. Primary source

    GitHub-reviewed advisory GHSA-4qv8-2p9j-2685 (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

  5. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-4qv8-2p9j-2685, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  6. Primary source

    FIRST measured EPSS score (opens a new tab)

    Measured EPSS probability and percentile for CVE-2026-109924, scored 2026-10-26. This is a model estimate, not proof of exposure.

    Published Checked

Cite this record

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

APA

KEVWire. (2026, October 23). undici vulnerable to Denial of Service via unbounded memory in the EventSource parser (CVE-2026-109924). https://kevwire.com/record/CVE-2026-109924

MLA

"undici vulnerable to Denial of Service via unbounded memory in the EventSource parser (CVE-2026-109924)." KEVWire, 23 Oct. 2026, kevwire.com/record/CVE-2026-109924.

Chicago

KEVWire. "undici vulnerable to Denial of Service via unbounded memory in the EventSource parser (CVE-2026-109924)." Last modified October 23, 2026. https://kevwire.com/record/CVE-2026-109924.

Evidence summary (plain text)

undici vulnerable to Denial of Service via unbounded memory in the EventSource parser (Oct 15, 2026).
undici is an HTTP client library for Node.js. In versions 6.5.0 through 6.29.0, 7.0.0 through 7.30.0, and 8.0.0 through 8.12.1, its 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 that the byte-based maxEventSize and maxResponseSize limits do not bound, and because maxResponseSize is enforced on the compressed body before decompression, a small compressed response can expand into enough retained memory to terminate the process. An application only needs to maintain an EventSource connection to an untrusted peer, which controls only the response, and availability is the only impact. The issue is fixed in undici 6.29.1, 7.30.1, and 8.12.2, which bound the retained parser state independently of the byte limits, and users should upgrade to one of those versions or later. There is no workaround.
CVSS 5.9 (version 3.1; evidence as of Oct 23, 2026; https://github.com/advisories/GHSA-4qv8-2p9j-2685).
EPSS 0.3% for the following 30 days, scored Oct 26, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-109924&date=2026-10-26).
Sources:
NVD CVE-2026-109924: https://nvd.nist.gov/vuln/detail/CVE-2026-109924
Vendor advisory (via NVD references): https://cna.openjsf.org/security-advisories.html
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?pubStartDate=2026-10-12T13:35:55.142Z&pubEndDate=2026-10-26T13:35:55.142Z&resultsPerPage=500&startIndex=3500
GitHub-reviewed advisory GHSA-4qv8-2p9j-2685: https://github.com/advisories/GHSA-4qv8-2p9j-2685
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
FIRST measured EPSS score: https://api.first.org/data/v1/epss?cve=CVE-2026-109924&date=2026-10-26
Record ID: CVE-2026-109924.
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: Oct 27, 2026, 01:40 UTC. Ingestion is not an independent editorial investigation.

NVD status: Analyzed. Publication in the NVD is not evidence of exploitation.

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.

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Record details

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