CVE-2026-84371: ApostropheCMS: Stored XSS via SVG SMIL URI-list scheme-policy bypass
ApostropheCMS is an open-source Node.js content management system, and sanitize-html provides a simple HTML sanitizer with a clear API. From version 1.9.0 until version 2.17.7, packages/sanitize-html/index.js validates an animation value attribute as one flat URL and does not recognize that attributeName selecting href or xlink:href gives the sibling values, from, to, or by attribute SVG SMIL URL semantics. In configurations that allow the animate, animateColor, animateMotion, animateTransform, or set elements, a values list can begin with a safe fragment and contain a later executable destination that survives allowedSchemesAppliedToAttributes checking. When the sanitized SVG is rendered, the browser can copy that later destination into the live link, and a victim who activates the link can execute script in the application's origin. This issue is fixed in version 2.17.7.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
ApostropheCMSto a version that resolves this vulnerability.Fixed in 2.17.7
Event History
Frequently Asked Questions
Which deployments are exposed to this issue?
Deployments using sanitize-html versions 1.9.0 through 2.17.6 are affected when their configuration allows SVG SMIL elements such as animate, animateColor, animateMotion, animateTransform, or set. The issue applies to ApostropheCMS and sanitize-html usage described in the advisory.
What must an attacker and victim do for exploitation to succeed?
An attacker needs the ability to store sanitized SVG content containing a crafted SMIL values list and an animation targeting href or xlink:href. A victim must render that SVG and activate the resulting link for script to execute in the application's origin.
Is the default sanitizer behavior affected?
The issue requires a configuration that allows the specified SVG SMIL elements. The provided information does not establish whether those elements are allowed by default.
What version fixes the vulnerability?
Upgrade sanitize-html to version 2.17.7 or later. Version 2.17.7 is identified as the fix.