Update dependency sanitize-html to v2.17.5 [SECURITY]

[renovate]

This PR contains the following updates:

Package	Change	Age	Confidence
sanitize-html (source)	2.17.1 → 2.17.5

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

CVE-2026-53606 / GHSA-vccv-cmxp-4j9h

More information

Details

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)

// 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:

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: <form action="javascript:alert(document.cookie)">
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: <form action="javascript:alert(document.cookie)">

Steps to Reproduce

const sanitize = require('sanitize-html');

// ===== VECTOR 1: form action (100% reliable, all modern browsers) =====
const v1 = sanitize(
    '<form action="javascript:alert(document.cookie)"><button>Submit</button></form>',
    {
        allowedTags: ['form', 'button'],
        allowedAttributes: { form: ['action'] }
    }
);
console.log('V1 (action):', v1);
// OUTPUT: <form action="javascript:alert(document.cookie)"><button>Submit</button></form>
// XSS triggers when user submits the form

// ===== VECTOR 2: button formaction (100% reliable) =====
const v2 = sanitize(
    '<button formaction="javascript:alert(1)">Click</button>',
    {
        allowedTags: ['button'],
        allowedAttributes: { button: ['formaction'] }
    }
);
console.log('V2 (formaction):', v2);
// OUTPUT: <button formaction="javascript:alert(1)">Click</button>

// ===== VECTOR 3: object data =====
const v3 = sanitize(
    '<object data="javascript:alert(1)"></object>',
    {
        allowedTags: ['object'],
        allowedAttributes: { object: ['data'] }
    }
);
console.log('V3 (data):', v3);
// OUTPUT: <object data="javascript:alert(1)"></object>

// ===== CONTROL: href IS scheme-checked (expected behavior) =====
const ctrl = sanitize(
    '<a href="javascript:alert(1)">click</a>',
    {
        allowedTags: ['a'],
        allowedAttributes: { a: ['href'] }
    }
);
console.log('Control (href):', ctrl);
// OUTPUT: <a>click</a>   ← href correctly stripped by naughtyHref()

Observed behavior: javascript: preserved on action/formaction/data but correctly stripped on href.

Expected behavior: javascript: should be stripped on ALL URI-bearing attributes, or at minimum, the library should warn developers when they allow URI-bearing attributes not covered by scheme validation.

Impact

An attacker can achieve XSS in applications that use sanitize-html with non-default configurations allowing URI-bearing attributes:

• <form action="javascript:..."> — XSS on form submission (all modern browsers)
• <button formaction="javascript:..."> — per-button XSS override (all modern browsers)
• <object data="javascript:..."> — object load XSS (Chrome, Firefox)
• <video poster="javascript:..."> — limited browser support but spec-valid

Common vulnerable configurations:

• CMS platforms allowing form elements for user-generated content
• Form builder applications
• Rich text editors with extended tag allowlists
• Email template editors allowing media/embed tags

Mitigating factors:

• Default configuration is NOT vulnerable
• Requires double opt-in: non-default tag + non-default attribute
• CSP form-action directive mitigates form-based vectors
• Developers CAN manually add attributes to allowedSchemesAppliedToAttributes

Remediation

Option 1 (Recommended): Expand the default allowedSchemesAppliedToAttributes list:

// index.js line 829, change from:
allowedSchemesAppliedToAttributes: ['href', 'src', 'cite'],

// to:
allowedSchemesAppliedToAttributes: [
    'href', 'src', 'cite', 'action', 'formaction',
    'data', 'poster', 'background', 'ping',
    'xlink:href', 'dynsrc', 'lowsrc'
],

Option 2: Apply naughtyHref() to ALL attributes by default (invert the gate logic).

Option 3: Add a runtime warning when developers allow URI-bearing attributes not in allowedSchemesAppliedToAttributes (analogous to vulnerableTags warning for script/style at lines 124-129).

Reporter

Kevin Lee (Changseon Lee)
OPCIA Corp. / PeanutAI Inc.
Seoul, South Korea
GitHub: crattack

Severity

• CVSS Score: 5.4 / 10 (Medium)
• Vector String: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

References

• https://github.com/apostrophecms/apostrophe/security/advisories/GHSA-vccv-cmxp-4j9h
• https://nvd.nist.gov/vuln/detail/CVE-2026-53606
• https://github.com/apostrophecms/apostrophe/pull/5464
• https://github.com/apostrophecms/apostrophe/commit/5a88e9630cbbdde33154ef8abe7557ddf7be418b
• https://github.com/apostrophecms/apostrophe/releases/tag/sanitize-html@2.17.5
• https://github.com/advisories/GHSA-vccv-cmxp-4j9h

This data is provided by the GitHub Advisory Database (CC-BY 4.0).

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Release Notes

apostrophecms/apostrophe (sanitize-html)

v2.17.5

Compare Source

v2.17.4

Compare Source

Changes

• sanitize-html and launder now share a single implementation of naughtyHref, based on that which previously existed in sanitize-html.

Security

• Security vulnerability: the xmp tag could be used to pass forbidden markup through sanitize-html, even when xmp itself is not explicitly allowed All users of sanitize-html should update immediately. Thanks to Vincenzo Turturro for reporting the vulnerability.

v2.17.3

Compare Source

Security

• Fix vulnerability introduced in version 2.17.2 that allowed XSS attacks if the developer chose to permit option tags. There was no vulnerability when not explicitly allowing option tags.

v2.17.2

Compare Source

Changes

• Upgrade htmlparser2 from 8.x to 10.1.0. This improves security by correctly decoding zero-padded numeric character references (e.g., &#​0000001) that previously bypassed javascript: URL detection. Also fixes double-encoding of entities inside raw text elements like textarea and option.

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