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High, CVSS 7.5amended

js-yaml: Exponential parsing time in flow collections leads to denial of service

CVE-2026-73643GHSA-pm4m-ph32-ghv5

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (js-yaml 5.2.2), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • npm js-yaml

    Affected
    >= 5.0.0, <= 5.2.1
    Fixed in
    5.2.2

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS
  • CVE-2026-73643: 0.49% estimated exploitation activity in the next 30 days; percentile 42.05 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary Parsing a small YAML document can take exponential time. An application that calls load() or loadAll() on untrusted input can be hung by a payload under 200 bytes. Details When an entry in a flow sequence turns out to be a key: value pair, the parser rewinds and parses that entry a second time as the key. If the key is itself a nested flow sequence of the same shape, every level is parsed twice, so the total work is O(2^n) in the nesting depth. The default maxDepth of 100 does not help, because the time is already unmanageable at about 30 to 40 levels. Root cause, potentially the: readFlowCollection in parser.ts, the restoreState followed by a second parseNode further down. PoC With default options: 22 levels takes about 1 second, 26 levels about 17 seconds, 30 levels over 2 minutes. The input stays under 200 bytes and grows linearly with n. Impact Denial of service. A single small request can keep one CPU busy for minutes or longer and blocks the Node event loop, so one…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from ghsa record GHSA-pm4m-ph32-ghv5

  2. Revision 1 · created ·

    Published from osv record GHSA-pm4m-ph32-ghv5

Agent brief

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# Patch Next advisory brief: CVE-2026-73643

Advisory: js-yaml: Exponential parsing time in flow collections leads to denial of service
IDs: CVE-2026-73643, GHSA-pm4m-ph32-ghv5
Record: https://patchnext.com/advisories/cve-2026-73643 (revision 2, source checked 26 Oct 2026, 13:01 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: js-yaml 5.2.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm js-yaml: affected >= 5.0.0, <= 5.2.1; fixed in 5.2.2

## Suggested inspection (read-only)
- `npm ls js-yaml --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 js-yaml.
- 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://osv.dev/vulnerability/GHSA-pm4m-ph32-ghv5 (OSV record GHSA-pm4m-ph32-ghv5 lists affected ranges: npm js-yaml >=5.0.0 <5.2.2 (fixed))
- Verified: https://github.com/advisories/GHSA-pm4m-ph32-ghv5 (GitHub-reviewed advisory GHSA-pm4m-ph32-ghv5 lists affected ranges: npm js-yaml >=5.0.0 <=5.2.1)

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