CVE-2026-59870: js-yaml is a JavaScript YAML parser and dumper

This week

HIGH 7.5REMOTEUPGRADE

CVE-2026-59870 is a high-severity flaw (CVSS 7.5) affecting js-yaml. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

js-yaml is a JavaScript YAML parser and dumper. Prior to 3.15.1, 4.3.1, and 5.2.1, YAML11_SCHEMA support for the !!omap tag in src/tag/sequence/omap.ts uses omapTag.addItem() to perform a linear duplicate-key scan on every insertion, causing O(n^2) CPU consumption when yaml.load() parses a crafted ordered-map document. In v3 and v4, !!omap is active and exploitable by default. v5 doesn't use !!omap by default, and the chances of activating it are

Why this priority

High severity
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.7% (top 46%)
CISA exploited list	No
Weakness	CWE-407, CWE-770
Published	2026-07-08
Last modified	2026-10-25

Publisher (CNA): GitHub, Inc. · Vendor: nodeca

Last updated 2026-10-25 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-08 16:16 UTCPublished CVE record published
2026-10-25 20:10 UTCUpdated Record last modified

nodeca js-yaml UPGRADE

Affected: >= 5.0.0 and < 5.2.1

Fixed in: 5.2.1

Safe to downgrade to: a release before 5.0.0

1. Check installed version

npm ls js-yaml

2. UPGRADE to 5.2.1

npm install js-yaml@">=5.2.1"

3. If no update is available yet, DOWNGRADE to a release before 5.0.0

npm view js-yaml versions npm install js-yaml@"<5.0.0"

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Exact fixes by distribution

npm · js-yaml · FIXED · 5.2.1 · vulnerable: >= 5.0.0, <= 5.2.0 · source

npm install js-yaml@">=5.2.1" npm ls js-yaml

Fedora 46 · python-apprise · FIXED · 2.1.0-1.fc46 · FEDORA-2026-ef67a72c5d · source

sudo dnf upgrade --advisory=FEDORA-2026-ef67a72c5d

Debian 12 · node-js-yaml · NOT AFFECTED

Debian 13 · node-js-yaml · NOT AFFECTED

RHEL 10 · grafana · NOT AFFECTED

RHEL 10 · rust · NOT AFFECTED

RHEL 7 · subscription-manager · NOT AFFECTED

RHEL 8 · grafana · NOT AFFECTED

RHEL 8 · mozjs60 · NOT AFFECTED

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-59870?

js-yaml: upgrade to 5.2.1. Exact commands for each OS are on this page.

Is CVE-2026-59870 being exploited?

CVE-2026-59870 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-59870 affect?

CVE-2026-59870 affects js-yaml. Severity is high (CVSS 7.5). js-yaml is a JavaScript YAML parser and dumper. Prior to 3.15.1, 4.3.1, and 5.2.1, YAML11_SCHEMA support for the !!omap tag in src/tag/sequence/omap.ts uses omapTag.addItem() to perform a linear duplicate-key scan on every insertion, causin

How urgent is CVE-2026-59870?

Priority 50/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

Related CVEs

CVE-2026-59869 HIGH 7.5 UPGRADE js-yaml is a JavaScript YAML parser and dumper
CVE-2026-59868 MEDIUM 5.3 UPGRADE js-yaml is a JavaScript YAML parser and dumper

References

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