What is CVE-2021-3377?

CVE-2021-3377 is a medium-severity cross-site scripting (XSS) vulnerability in ansi_up (npm), affecting versions < 5.0.0. It is fixed in 5.0.0. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.

How severe is CVE-2021-3377?

CVE-2021-3377 has a CVSS score of 6.1 (Medium). 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 ansi_up are affected by CVE-2021-3377?

ansi_up (npm) versions < 5.0.0 is affected.

Is there a fix for CVE-2021-3377?

Yes. CVE-2021-3377 is fixed in 5.0.0. Upgrade to this version or later.

Is CVE-2021-3377 exploitable, and should I be worried?

Whether CVE-2021-3377 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-2021-3377 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.

CVE-2021-3377 in ansi_up

Q: How severe is CVE-2021-3377?

CVE-2021-3377 has a CVSS score of 6.1 (Medium). 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 ansi_up are affected by CVE-2021-3377?

ansi_up (npm) versions < 5.0.0 is affected.

Q: Is there a fix for CVE-2021-3377?

Yes. CVE-2021-3377 is fixed in 5.0.0. Upgrade to this version or later.

Q: Is CVE-2021-3377 exploitable, and should I be worried?

Whether CVE-2021-3377 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-2021-3377 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-2021-3377?

Upgrade ansi_up to 5.0.0 or later.

Summary

ansi_up cross-site scripting vulnerability

The npm package ansi_up converts ANSI escape codes into HTML. In ansi_up v4, ANSI escape codes can be used to create HTML hyperlinks. Due to insufficient URL sanitization, this feature is affected by a cross-site scripting (XSS) vulnerability. This issue is fixed in v5.0.0.

Impact

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-2021-3377 has a CVSS score of 6.1 (Medium). 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 (5.0.0); upgrading removes the vulnerable code path.

Affected versions

ansi_up (< 5.0.0)

Security releases

ansi_up → 5.0.0 (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

Upgrade ansi_up to 5.0.0 or later to resolve this vulnerability.

Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.

Frequently Asked Questions

What is CVE-2021-3377? CVE-2021-3377 is a medium-severity cross-site scripting (XSS) vulnerability in ansi_up (npm), affecting versions < 5.0.0. It is fixed in 5.0.0. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
How severe is CVE-2021-3377? CVE-2021-3377 has a CVSS score of 6.1 (Medium). 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 ansi_up are affected by CVE-2021-3377? ansi_up (npm) versions < 5.0.0 is affected.
Is there a fix for CVE-2021-3377? Yes. CVE-2021-3377 is fixed in 5.0.0. Upgrade to this version or later.
Is CVE-2021-3377 exploitable, and should I be worried? Whether CVE-2021-3377 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-2021-3377 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-2021-3377? Upgrade ansi_up to 5.0.0 or later.