markdown-it: Quadratic complexity DoS in smartquotes rule via replaceAt string operations

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2026-48988: 0.38% estimated exploitation activity in the next 30 days; percentile 31.90 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary A quadratic time complexity vulnerability exists in markdown-it's smartquotes rule (enabled via the typographer: true option). An attacker can craft a markdown input consisting of consecutive quotation marks that causes the parser to consume excessive CPU time, leading to denial of service. Details The vulnerability is in the replaceAt() helper function used by the smartquotes rule in lib/rulescore/smartquotes.mjs: When markdown-it processes a text token containing many quotation marks (either " or ') with typographer: true, the smartquotes rule iterates through each quote character and calls replaceAt() to substitute it with a typographic (curly) quote. Each call to replaceAt() creates three new string slices and concatenates them, which is an O(n) operation where n is the length of the string. Since this is called once per quote character in the token, and there are n quote characters, the total time complexity becomes O(n^2). The root cause is that the smartquotes rule…

Published by the source

15 Jun 2026, 20:41 UTC

Last modified by the source

10 Sep 2026, 03:51 UTC

Source last checked

26 Oct 2026, 12:55 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-6v5v-wf23-fmfq

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-6v5v-wf23-fmfq

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-48988

Advisory: markdown-it: Quadratic complexity DoS in smartquotes rule via replaceAt string operations
IDs: CVE-2026-48988, GHSA-6v5v-wf23-fmfq
Record: https://patchnext.com/advisories/cve-2026-48988 (revision 2, source checked 26 Oct 2026, 12:55 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: markdown-it 14.2.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm markdown-it: affected <= 14.1.1; fixed in 14.2.0

## 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://osv.dev/vulnerability/GHSA-6v5v-wf23-fmfq (OSV record GHSA-6v5v-wf23-fmfq lists affected ranges: npm markdown-it >=0 <14.2.0 (fixed))
- Verified: https://github.com/advisories/GHSA-6v5v-wf23-fmfq (GitHub-reviewed advisory GHSA-6v5v-wf23-fmfq lists affected ranges: npm markdown-it >=0 <=14.1.1)

Commands are suggestions: review each one before running it.