NVD / CVE Program· CNA GitHub_M

CVE-2026-84375: js-yaml: maxTotalMergeKeys does not limit CPU use for empty merge sources

Noroxi assessment

Priority: Monitor (action score 30/100)

The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
Probability of exploitation in the next 30 days: 0.54% (FIRST EPSS).
Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
According to CISA the attack is automatable: targets can be found by mass scanning.
Fixed version: node-js-yaml (Debian:14) 4.3.2+~4.0.9-1; js-yaml (npm) 3.15.2, 4.3.2; grafana12.4 (Red Hat:hummingbird:1) 0:12.4.9-0.5.hum1.

Low priority for now. Upgrade to node-js-yaml (Debian:14) 4.3.2+~4.0.9-1; js-yaml (npm) 3.15.2, 4.3.2; grafana12.4 (Red Hat:hummingbird:1) 0:12.4.9-0.5.hum1 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

js-yaml is a JavaScript YAML parser and dumper. From 3.0.0 until 3.15.2, 4.3.2, and 5.4.1, maxTotalMergeKeys in lib/js-yaml/loader.js and lib/loader.js does not count empty mapping sources while processing the merge key <<. An attacker can alias a large sequence of empty mappings into many merge targets, causing O(N * K) processing while totalMergeKeys remains unchanged and the configured resource limit is never reached. A relatively small YAML document can therefore cause prolonged CPU consumption in applications that parse untrusted YAML, and merge processing is enabled by default on these release lines. In v3 & v4, merge is enabled by default so the severity score is higher. This issue is fixed in versions 3.15.2, 4.3.2, and 5.4.1.

HighCVSS 7.5 · v3.1—No exploit Fix available

Published: Sep 1, 2026
Updated: Sep 28, 2026
EPSS: 0.5% · 45th percentile
CWE: CWE-400

Report tools

JSON

Action score

Monitor

Low priority for now.

CVSS: 30 / 40 · 7.5 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.5%

CISA SSVC decision

Exploitation: none
Automatable: yes
Technical impact: partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: —
CNA · GitHub_M: 7.5; NVD has not scored this yet; the score shown is the CNA’s.

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

Not in KEV: no record of exploitation in the wild
No public exploit code on record
A fix has been released

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

—

Versions reported by the vendor

Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.

nodeca js-yaml
- >= 3.0.0, < 3.15.2, >= 4.0.0, < 4.3.2, >= 5.0.0, < 5.4.1affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Ecosystem	Package	Affected range	Fix
Debian:12	node-js-yaml	from 0	—
Debian:14	node-js-yaml	before 4.3.2+~4.0.9-1	4.3.2+~4.0.9-1
npm	js-yaml	from 3.0.0 · before 3.15.2	3.15.2
npm	js-yaml	from 4.0.0 · before 4.3.2	4.3.2
Red Hat:hummingbird:1	grafana12.4	before 0:12.4.9-0.5.hum1	0:12.4.9-0.5.hum1
Red Hat:hummingbird:1	grafana13.1	before 0:13.1.3-0.5.hum1	0:13.1.3-0.5.hum1
Red Hat:hummingbird:1	grafana13.2	before 0:13.2.0-0.1.4.hum1	0:13.2.0-0.1.4.hum1
Red Hat:hummingbird:1	grafana13.2	before 0:13.2.1-0.1.hum1	0:13.2.1-0.1.hum1

Same product

nodeca: all records

Other highest-scoring records for the same primary product.

CVE-2013-4660The JS-YAML module before 2.0.5 for Node.js parses input without properly considering the unsafe !!js/function tag, which allows remote atta
40Plan
CVE-2026-73643js-yaml: Exponential parsing time in the flow collections leads to denial of service
30Monitor
CVE-2026-59870js-yaml quadratic-complexity denial of service via YAML11_SCHEMA !!omap parsing
30Monitor

Published before and after this one in the same product

← EarlierCVE-2026-53550Jun 22, 2026 · js-yaml: Quadratic-complexity DoS in merge key handling via repeated aliases
21Monitor
← EarlierCVE-2026-59868Jul 8, 2026 · js-yaml: YAML merge-key chains can force quadratic CPU consumption
30Monitor
← EarlierCVE-2026-59869Jul 8, 2026 · js-yaml: YAML merge-key chains can force quadratic CPU consumption
30Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / package	Fixed version	Source
debian:node-js-yaml	4.3.2+~4.0.9-1 · Debian:14	Package registry (OSV)
npm:js-yaml	3.15.2	Package registry (OSV)
npm:js-yaml	4.3.2	Package registry (OSV)
red hat:grafana12.4	0:12.4.9-0.5.hum1 · Red Hat:hummingbird:1	Package registry (OSV)
red hat:grafana13.1	0:13.1.3-0.5.hum1 · Red Hat:hummingbird:1	Package registry (OSV)
red hat:grafana13.2	0:13.2.0-0.1.4.hum1 · Red Hat:hummingbird:1	Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

Anyone who can reach it over the internet can trigger it.
No account or password is required.
No user action is required.
No special conditions are required; it is repeatable.

If successful

Confidentiality: none
Integrity: none
Availability: high · the service can be disrupted

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality impact: None
Integrity impact: None
Availability impact: High

Weakness class (CWE)

CWE-400 · Uncontrolled Resource Consumption

CVSS vector

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

nvd-secondary

Root cause

Code that parses nested structures sets no depth or size limit. A small input can turn into a disproportionate processing load.

The bug in code

The whole CWE-400 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1function expand(node) {
2  return node.children.map(expand);
3}

Fixed

1const MAX_DEPTH = 32;
2function expand(node, depth = 0) {
3  if (depth > MAX_DEPTH) throw new Error("too deep");
4  return node.children.map((c) => expand(c, depth + 1));
5}

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Attack patterns (CAPEC)

ATT&CK techniques

Endpoint Denial of ServiceT1499

Change log

Fix✗ → ✓Sep 28, 2026, 10:48 PM UTC

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References

github.com/nodeca/js-yaml/commit/3485bc06ff8a0251505f44a00414d90df2466639

Show all references (7 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

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