ApostropheCMS: Client-side Prototype Pollution in apos.http.parseQuery leading to DOM-based XSS against authenticated users

Exploitation

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

CVSS

6.1 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

EPSS

• CVE-2026-113659: 0.34% estimated exploitation activity in the next 30 days; percentile 28.09 (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 The client-side helper apos.http.parseQuery() in ApostropheCMS builds a nested object from a URL query string without sanitizing the keys proto, constructor, or prototype. Parsing an attacker-controlled query string therefore writes arbitrary properties onto Object.prototype (client-side prototype pollution). ApostropheCMS's admin UI calls this parser with window.location.search on every authenticated page load (the admin context bar's data() initializer). Because the admin UI is built on Vue, a polluted, enumerable property on Object.prototype is then picked up by Vue's standard element-mount routine and written to the DOM as an element property, turning the prototype pollution into DOM-based XSS in the victim's authenticated session. The escalation gadget is a well-known, general Vue behavior; the novel, reportable defect is the unsanitized parseQuery source together with the authenticated trigger, both of which are ApostropheCMS code. Any user who can get any logged-in…

Published by the source

20 Oct 2026, 18:18 UTC

Last modified by the source

20 Oct 2026, 18:30 UTC

Source last checked

26 Oct 2026, 13:07 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-m2m5-rw3w-cwmj

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-m2m5-rw3w-cwmj

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-m2m5-rw3w-cwmj

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# Patch Next advisory brief: CVE-2026-113659

Advisory: ApostropheCMS: Client-side Prototype Pollution in apos.http.parseQuery leading to DOM-based XSS against authenticated users
IDs: CVE-2026-113659, GHSA-m2m5-rw3w-cwmj
Record: https://patchnext.com/advisories/cve-2026-113659 (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: Medium (CVSS 6.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: apostrophe 4.33.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm apostrophe: affected < 4.33.0; fixed in 4.33.0

## Suggested inspection (read-only)
- `npm ls apostrophe --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 apostrophe.
- 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-m2m5-rw3w-cwmj (GitHub-reviewed advisory GHSA-m2m5-rw3w-cwmj lists affected ranges: npm apostrophe >=0 <4.33.0)
- Verified: https://osv.dev/vulnerability/GHSA-m2m5-rw3w-cwmj (OSV record GHSA-m2m5-rw3w-cwmj lists affected ranges: npm apostrophe >=0 <4.33.0 (fixed))

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