What is CVE-2021-43307?

CVE-2021-43307 is a low-severity inefficient regular expression (ReDoS) vulnerability in semver-regex (npm), affecting versions < 3.1.4. It is fixed in 3.1.4, 4.0.3. A regular expression with worst-case exponential or polynomial matching time is applied to untrusted input, causing excessive CPU use.

Which versions of semver-regex are affected by CVE-2021-43307?

semver-regex (npm) versions < 3.1.4 is affected.

Is there a fix for CVE-2021-43307?

Yes. CVE-2021-43307 is fixed in 3.1.4, 4.0.3. Upgrade to this version or later.

Is CVE-2021-43307 exploitable, and should I be worried?

Whether CVE-2021-43307 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-2021-43307 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-2021-43307?

Upgrade: semver-regex to 3.1.4 or later, semver-regex to 4.0.3 or later.

CVE-2021-43307 in semver-regex

Q: Which versions of semver-regex are affected by CVE-2021-43307?

semver-regex (npm) versions < 3.1.4 is affected.

Q: Is there a fix for CVE-2021-43307?

Yes. CVE-2021-43307 is fixed in 3.1.4, 4.0.3. Upgrade to this version or later.

Q: Is CVE-2021-43307 exploitable, and should I be worried?

Whether CVE-2021-43307 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-2021-43307 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-2021-43307?

Upgrade: semver-regex to 3.1.4 or later, semver-regex to 4.0.3 or later.

Summary

Regular expression denial of service in semver-regex

An exponential ReDoS (Regular Expression Denial of Service) can be triggered in the semver-regex npm package, when an attacker is able to supply arbitrary input to the test() method

Impact

A regular expression with worst-case exponential or polynomial matching time is applied to untrusted input, causing excessive CPU use. Typical impact: denial of service when input is crafted to trigger backtracking.

Affected versions

semver-regex (< 3.1.4) semver-regex (>= 4.0.0, < 4.0.3)

Security releases

semver-regex → 3.1.4 (npm) semver-regex → 4.0.3 (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 the following packages to resolve this vulnerability:

semver-regex to 3.1.4 or later; semver-regex to 4.0.3 or later

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

Frequently Asked Questions

What is CVE-2021-43307? CVE-2021-43307 is a low-severity inefficient regular expression (ReDoS) vulnerability in semver-regex (npm), affecting versions < 3.1.4. It is fixed in 3.1.4, 4.0.3. A regular expression with worst-case exponential or polynomial matching time is applied to untrusted input, causing excessive CPU use.
Which versions of semver-regex are affected by CVE-2021-43307? semver-regex (npm) versions < 3.1.4 is affected.
Is there a fix for CVE-2021-43307? Yes. CVE-2021-43307 is fixed in 3.1.4, 4.0.3. Upgrade to this version or later.
Is CVE-2021-43307 exploitable, and should I be worried? Whether CVE-2021-43307 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-2021-43307 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-2021-43307?
- Upgrade semver-regex to 3.1.4 or later
- Upgrade semver-regex to 4.0.3 or later

Other vulnerabilities in semver-regex

CVE-IDSeverityPackage summary

CVE-2021-3795Highsemver-regex: semver-regex Regular Expression Denial of Service (ReDOS)