Summary
Cross-Site Scripting in Prism
Workarounds
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.
References
The vulnerability was introduced by this commit on Sep 29, 2015 and fixed by Masato Kinugawa (#2506).
For more information
If you have any questions or comments about this advisory, please open an issue.
Impact
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).
Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.
CVE-2020-15138 has a CVSS score of 7.1 (High). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.21.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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This problem is patched in v1.21.0.
Frequently Asked Questions
- What is CVE-2020-15138? CVE-2020-15138 is a high-severity cross-site scripting (XSS) vulnerability in prismjs (npm), affecting versions >= 1.1.0, < 1.21.0. It is fixed in 1.21.0. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
- How severe is CVE-2020-15138? CVE-2020-15138 has a CVSS score of 7.1 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of prismjs are affected by CVE-2020-15138? prismjs (npm) versions >= 1.1.0, < 1.21.0 is affected.
- Is there a fix for CVE-2020-15138? Yes. CVE-2020-15138 is fixed in 1.21.0. Upgrade to this version or later.
- Is CVE-2020-15138 exploitable, and should I be worried? Whether CVE-2020-15138 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2020-15138 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2020-15138? Upgrade
prismjsto 1.21.0 or later.