What is CVE-2021-39199?

CVE-2021-39199 is a critical-severity cross-site scripting (XSS) vulnerability in remark-html (npm), affecting versions < 13.0.2. It is fixed in 13.0.2, 14.0.1. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.

How severe is CVE-2021-39199?

CVE-2021-39199 has a CVSS score of 10.0 (Critical). 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 remark-html are affected by CVE-2021-39199?

remark-html (npm) versions < 13.0.2 is affected.

Is there a fix for CVE-2021-39199?

Yes. CVE-2021-39199 is fixed in 13.0.2, 14.0.1. Upgrade to this version or later.

Is CVE-2021-39199 exploitable, and should I be worried?

Whether CVE-2021-39199 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.

What actually determines whether CVE-2021-39199 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-2021-39199?

Upgrade: remark-html to 13.0.2 or later, remark-html to 14.0.1 or later.

CVE-2021-39199 in remark-html

Q: How severe is CVE-2021-39199?

CVE-2021-39199 has a CVSS score of 10.0 (Critical). 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.

Q: Which versions of remark-html are affected by CVE-2021-39199?

remark-html (npm) versions < 13.0.2 is affected.

Q: Is there a fix for CVE-2021-39199?

Yes. CVE-2021-39199 is fixed in 13.0.2, 14.0.1. Upgrade to this version or later.

Q: Is CVE-2021-39199 exploitable, and should I be worried?

Whether CVE-2021-39199 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.

Q: What actually determines whether CVE-2021-39199 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.

Q: How do I fix CVE-2021-39199?

Upgrade: remark-html to 13.0.2 or later, remark-html to 14.0.1 or later.

Summary

Unsafe defaults in remark-html

Workarounds

On older affected versions, pass sanitize: true, like so:

-  .use(remarkHtml)
+  .use(remarkHtml, {sanitize: true})

References

n/a

For more information

If you have any questions or comments about this advisory:

Open an issue in remark-html
Email us at [email protected]

Impact

The documentation of remark-html has mentioned that it was safe by default. In practise the default was never safe and had to be opted into. This means arbitrary HTML can be passed through leading to potential XSS attacks.

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-2021-39199 has a CVSS score of 10.0 (Critical). The vector is network-reachable, no privileges required, and no user interaction. 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 (13.0.2, 14.0.1); upgrading removes the vulnerable code path.

Affected versions

remark-html (< 13.0.2) remark-html (= 14.0.0)

Security releases

remark-html → 13.0.2 (npm) remark-html → 14.0.1 (npm)

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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Remediation advice

The problem has been patched in 13.0.2 and 14.0.1: remark-html is now safe by default, and the implementation matches the documentation.

Frequently Asked Questions

What is CVE-2021-39199? CVE-2021-39199 is a critical-severity cross-site scripting (XSS) vulnerability in remark-html (npm), affecting versions < 13.0.2. It is fixed in 13.0.2, 14.0.1. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
How severe is CVE-2021-39199? CVE-2021-39199 has a CVSS score of 10.0 (Critical). 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 remark-html are affected by CVE-2021-39199? remark-html (npm) versions < 13.0.2 is affected.
Is there a fix for CVE-2021-39199? Yes. CVE-2021-39199 is fixed in 13.0.2, 14.0.1. Upgrade to this version or later.
Is CVE-2021-39199 exploitable, and should I be worried? Whether CVE-2021-39199 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-2021-39199 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-2021-39199?
- Upgrade remark-html to 13.0.2 or later
- Upgrade remark-html to 14.0.1 or later