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High, CVSS 8.7amended

LinkifyIt#match scan loop has quadratic algorithmic complexity

CVE-2026-48801GHSA-22p9-wv53-3rq4

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (linkify-it 5.0.1), 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

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
8.7 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N · score source
EPSS
  • CVE-2026-48801: 0.39% estimated exploitation activity in the next 30 days; percentile 33.61 (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 LinkifyIt.prototype.match — the package's primary public API — has O(N²) algorithmic complexity for inputs containing many fuzzy links or emails. This is not a regex backtrack bug; it's a structural issue in the JS-level scan loop that re-slices the input and re-runs unanchored regex searches on progressively shorter tails, N times. 64 KB of "a@b.com\n" repeated burns ~2.5 s of single-threaded CPU; 128 KB takes ~10 s. Doubling the input quadruples the time — textbook O(N²). The same cost passes through markdown-it (linkify:true) unmodified. Any service that synchronously renders untrusted Markdown with linkify enabled on a request hot-path (forums, comments, chat, wikis, AI chat UIs) inherits a worker-process DoS triggerable by a tens-of-KB request body. Affected component - HEAD audited: 8e887d5bace3f5b09b1d1f70492fa0364ef1793d (v5.0.0) - Vulnerable function: LinkifyIt.prototype.match — index.mjs:528-554 - Re-scan call sites inside test(): index.mjs:444 (fuzzy host search),…

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

    Amended from ghsa record GHSA-22p9-wv53-3rq4

  2. Revision 2 · amended ·

    Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

  3. Revision 1 · created ·

    Published from osv record GHSA-22p9-wv53-3rq4

Agent brief

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# Patch Next advisory brief: CVE-2026-48801

Advisory: LinkifyIt#match scan loop has quadratic algorithmic complexity
IDs: CVE-2026-48801, GHSA-22p9-wv53-3rq4
Record: https://patchnext.com/advisories/cve-2026-48801 (revision 3, source checked 26 Oct 2026, 12:56 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: linkify-it 5.0.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm linkify-it: affected <= 5.0.0; fixed in 5.0.1

## Suggested inspection (read-only)
- `npm ls linkify-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 linkify-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-22p9-wv53-3rq4 (OSV record GHSA-22p9-wv53-3rq4 lists affected ranges: npm linkify-it >=0 <5.0.1 (fixed))
- Verified: https://github.com/advisories/GHSA-22p9-wv53-3rq4 (GitHub-reviewed advisory GHSA-22p9-wv53-3rq4 lists affected ranges: npm linkify-it >=0 <=5.0.0)

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