CVE-2020-15138
HIGHCVE-2020-15138 is a high-severity (CVSS 7.5) Cross-site Scripting (XSS) vulnerability in prismjs. O3 Security confirms whether CVE-2020-15138 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Cross-Site Scripting in Prism
Blast Radius
Weekly download volume for affected packages — a proxy for how broadly this vulnerability is deployed.
prismjsnpmDescription
Prism is vulnerable to Cross-Site Scripting. The easing preview of the Previewers plugin has an XSS vulnerability that allows attackers to execute arbitrary code in Safari and Internet Explorer. This impacts all Safari and Internet Explorer users of Prism >=v1.1.0 that use the Previewers plugin (>=v1.10.0) or the Previewer: Easing plugin (v1.1.0 to v1.9.0). This problem is fixed in version 1.21.0. To workaround the issue without upgrading, disable the easing preview on all impacted code blocks. You need Prism v1.10.0 or newer to apply this workaround.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | prismjs | ≥ 1.1.0&&< 1.21.0 | 1.21.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for prismjs. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update prismjs to 1.21.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-15138 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2020-15138 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2020-15138. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2020-15138 in your dependencies?
O3 detects CVE-2020-15138 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.