CVE-2026-35569 ApostropheCMS: Stored XSS in SEO Fields Leads to Authenticated API Data Exposure in ApostropheCMS
Stored XSS in ApostropheCMS SEO fields allows attackers to execute scripts and exfiltrate sensitive user data from authenticated sessions.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-35569?
CVE-2026-35569 is a high-severity cross-site scripting vulnerability in apostrophecms apostrophe, published on 15 Apr 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Official description
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.
Which versions are affected by CVE-2026-35569?
2 open source packages ship an affected version, including apostrophe. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
apostrophe npm | All versions | 4.29.0 |
apostrophe npm | All versions | 4.29.0 |
Products include Apostrophecms Apostrophecms.
How do I fix CVE-2026-35569?
Upgrade apostrophe to 4.29.0 or later.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-35569 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-35569 exists.
Other vulnerabilities in apostrophecms apostrophe
- CVE-2021-25979 Apostrophe - Insufficient Session Expiration
- CVE-2026-32730 ApostropheCMS MFA/TOTP Bypass via Incorrect MongoDB Query in Bearer Token Middleware
- CVE-2026-40186 ApostropheCMS: sanitize-html allowedTags Bypass via Entity-Decoded Text in nonTextTags Elements
- CVE-2026-33889 ApostropheCMS: Stored XSS via CSS Custom Property Injection in `@apostrophecms/color-field` Escaping Style Tag Context
- CVE-2021-25978 Apostrophe - XSS
Sources
Also known as GHSA-855c-r2vq-c292.