CVE-2026-53606

sanitize-html has incomplete URI scheme validation in that allows javascript: URIs through action, formaction, data, poster, and background attributes

Published

2026-07-31

Modified

2026-07-31

EPSS percentile

3%

Aliases

GHSA-vccv-cmxp-4j9h

Sources

github-advisory

Summary

## Summary sanitize-html uses `allowedSchemesAppliedToAttributes` (default: `['href', 'src', 'cite']`) to gate the `naughtyHref()` function that blocks dangerous URI schemes like `javascript:` and `vbscript:`. The HTML specification defines 10+ attributes that accept URIs (`action`, `formaction`, `data`, `poster`, `background`, `ping`, `xlink:href`, `dynsrc`, `lowsrc`), but none of these are included in the default gate list. When a developer allows any of these attributes in their configuration, `javascript:` URIs pass through completely unmodified, enabling XSS. The library has zero awareness of these URI-bearing attributes — none appear anywhere in the 854-line source file (verified by grep). No warning mechanism exists, and the README provides no security guidance about expanding `allowedSchemesAppliedToAttributes` when allowing form or media attributes. ## Severity Exploitation requires non-default configuration: the developer must explicitly allow a non-default tag (e.g., `form`) AND a non-default attribute (e.g., `action`). Default configuration is NOT vulnerable. However, this is a common configuration pattern for CMS platforms, form builders, and rich content editors. ## Affected Versions All versions of sanitize-html from v1.18.0 (which introduced `allowedSchemesAppliedToAttributes`) through at least v2.17.2. The default list has been `['href', 'src', 'cite']` since introduction and has never been expanded. ## Root Cause **File**: `index.js:329` (sanitize-html 2.10.0, confirmed same in 2.17.x) ```javascript // Line 329 — The gate that controls scheme validation if (options.allowedSchemesAppliedToAttributes.indexOf(a) >= 0) { if (naughtyHref(name, value)) { delete frame.attribs[a]; return; } } ``` **Default list at line 829**: ```javascript allowedSchemesAppliedToAttributes: ['href', 'src', 'cite'], ``` The `naughtyHref()` function (lines 627-667) correctly blocks `javascript:`, `vbscript:`, and other dangerous schemes. However, it has exactly 2 call sites in the entire codebase (lines 330 and 395), both inside the `indexOf` gate. There is no ungated path. When attribute name is `action`, `formaction`, `data`, `poster`, `background`, etc.: - `indexOf('action')` returns `-1` - The `if` block is skipped entirely - `naughtyHref()` is never called - `javascript:alert(1)` passes through unmodified The `escapeHtml()` function at line 464 provides no defense — it only encodes `& "` characters, which are not present in `javascript:alert(1)`. **Data Flow**: ``` Attacker input: 1. htmlparser2 parses → tag='form', attribs={action:'javascript:alert(document.cookie)'} 2. index.js:298 → allowedAttributes check: 'action' in developer config → PASS 3. index.js:329 → ['href','src','cite'].indexOf('action') → -1 → SKIP naughtyHref() 4. index.js:464 → escapeHtml('javascript:alert(document.cookie)') → unchanged 5. OUTPUT: ``` ## Steps to Reproduce ```javascript const sanitize = require('sanitize-html'); // ===== VECTOR 1: form action (100% reliable, all modern browsers) ===== const v1 = sanitize( ' Submit ', { allowedTags: ['form', 'button'], allowedAttributes: { form: ['action'] } } ); console.log('V1 (action):', v1); // OUTPUT: Submit // XSS triggers when user submits the form // ===== VECTOR 2: button formaction (100% reliable) ===== const v2 = sanitize( ' Click ', { allowedTags: ['button'], allowedAttributes: { button: ['formaction'] } } ); console.log('V2 (formaction):', v2); // OUTPUT: Click // ===== VECTOR 3: object data ===== const v3 = sanitize( ' </objec

Affected packages

Remediation: Upgrade to 2.17.5 or later.

References

• https://github.com/advisories/GHSA-vccv-cmxp-4j9h