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High, CVSS 7.5amended

markdown-it: Quadratic-time rendering of a single multi-line link reference definition with default options (regression since 14.0)

CVE-2026-111758GHSA-gfr2-rv44-r23c

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (markdown-it 15.0.3, 14.3.3), 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 markdown-it

    Affected
    >= 14.1.0, < 14.3.3>= 15.0.0, < 15.0.3
    Fixed in
    15.0.3, 14.3.3

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-2026-111758: 0.55% estimated exploitation activity in the next 30 days; percentile 46.08 (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 A link reference definition whose label or title is never closed is O(n²) in markdown-it 15.0.2 with default options. Continuation lines are pulled lazily with str += lineContent in src/rulesblock/reference.ts, and the subsequent charCodeAt and slice calls flatten the V8 cons-string, copying everything collected so far; this runs before the rule decides the definition is invalid. It is a regression introduced by PR #1004 in 14.0.0: 13.0.2 processed a 313 KB input in 125 ms, while every version since takes about 11 seconds on the same input. At the sizes below, 200 KB takes 3.6 seconds, 400 KB takes 18.1 seconds, and 800 KB takes 74.0 seconds, which is roughly 4–5× per doubling. No options are required to trigger it. Details src/rulesblock/reference.ts appends continuation lines with str += lineContent at lines 74, 83, 100, 133, and 150, then keeps indexing the accumulated string via str.charCodeAt(pos) in the label and whitespace loops and str.slice(...) in parseLinkTitle. V8…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 3 · amended ·

    Amended from ghsa record GHSA-gfr2-rv44-r23c

  2. Revision 2 · amended ·

    Amended from osv record GHSA-gfr2-rv44-r23c

  3. Revision 1 · created ·

    Published from ghsa record GHSA-gfr2-rv44-r23c

Agent brief

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# Patch Next advisory brief: CVE-2026-111758

Advisory: markdown-it: Quadratic-time rendering of a single multi-line link reference definition with default options (regression since 14.0)
IDs: CVE-2026-111758, GHSA-gfr2-rv44-r23c
Record: https://patchnext.com/advisories/cve-2026-111758 (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: 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: markdown-it 15.0.3, 14.3.3. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm markdown-it: affected >= 14.1.0, < 14.3.3; >= 15.0.0, < 15.0.3; fixed in 15.0.3, 14.3.3

## Suggested inspection (read-only)
- `npm ls markdown-it --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 markdown-it.
- 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-gfr2-rv44-r23c (GitHub-reviewed advisory GHSA-gfr2-rv44-r23c lists affected ranges: npm markdown-it >=14.1.0 =15.0.0 <15.0.3)
- Verified: https://osv.dev/vulnerability/GHSA-gfr2-rv44-r23c (OSV record GHSA-gfr2-rv44-r23c lists affected ranges: npm markdown-it >=14.1.0 =15.0.0 <15.0.3 (fixed))

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