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MEDIUM severity

Cross-site Scripting in reveal.jsGHSA-6vwx-mwp8-fh44

MEDIUM

GHSA-6vwx-mwp8-fh44 is a medium-severity (CVSS 6.1) Cross-site Scripting (XSS) vulnerability in reveal.js. 1 public exploit reference exists, so weaponization risk is real. A fix is available for reveal.js — see the affected versions and patch details below.

Also known asCVE-2020-8127
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
1 known
Exploitation data as of Oct 11, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
1.2%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs67th percentile — riskier than 67% of all scored CVEsHighest risk
0.03%0.59%1.14%1.70%0.5%1.2%Apr 26Aug 26Oct 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

GHSA-6vwx-mwp8-fh44 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,987 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

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.

158other npm packages depend on this — each one inherits the vulnerability until it's patched upstream
reveal.jsnpm
153Kdownloads / week

Description

Insufficient validation in cross-origin communication (postMessage) in reveal.js version 3.9.1 and earlier allow attackers to perform cross-site scripting attacks.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
📦npmreveal.jsall versions3.9.2npm install reveal.js@3.9.2

Affected Products

1 product · 1 configurations
Application
reveal.jsrevealjs
≤ 3.9.1
range
Exploits & PoCs
1

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

Insufficient validation in cross-origin communication (postMessage) in r…

hackerone.comNVDMar 2020

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for reveal.js, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update reveal.js to 3.9.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-6vwx-mwp8-fh44 is resolved across your whole dependency graph.

  3. 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

Insufficient validation in cross-origin communication (postMessage) in reveal.js version 3.9.1 and earlier allow attackers to perform cross-site scripting attacks.
O3 Security · Impact-Aware SCA

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Cross-site Scripting in reveal.js (Medium 6.1)