Summary
Regular Expression Denial-of-Service in npm schema-inspector
Workarounds
Is there a way for users to fix or remediate the vulnerability without upgrading?
If a user chooses to not upgrade, the only known workaround would be to stop using the email validation feature in the library. The user could, for example, accept the email address into their system but save it in a "not yet validated" state in their system until a verification email is sent to it (to determine whether the email is valid and belongs to the form submitter). Note that this is the preferred way of validating email addresses anyways.
References
Are there any links users can visit to find out more?
https://gist.github.com/mattwelke/b7f42424680a57b8161794ad1737cd8f
For more information
If you have any questions or comments about this advisory, you can create an issue in this repository.
Impact
What kind of vulnerability is it? Who is impacted?
Email address validation is vulnerable to a denial-of-service attack where some input (for example a@0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.) will freeze the program or web browser page executing the code. This affects any current schema-inspector users using any version to validate email addresses. Users who do not do email validation, and instead do other types of validation (like string min or max length, etc), are not affected.
The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths. Typical impact: varies by context: data corruption, logic bypass, or denial of service.
CVE-2021-21267 has a CVSS score of 7.5 (High). 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 (2.0.0); 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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Has the problem been patched? What versions should users upgrade to?
Users should upgrade to version 2.0.0, which uses a regex expression that isn't vulnerable to ReDoS. The new regex expression is more limited in what it can check, so it is more flexible than the one used before. Therefore, this was a new major version instead of a new patch version to warn people upgrading that they should make sure the email validation still works for their use case.
Frequently Asked Questions
- What is CVE-2021-21267? CVE-2021-21267 is a high-severity improper input validation vulnerability in schema-inspector (npm), affecting versions < 2.0.0. It is fixed in 2.0.0. The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths.
- How severe is CVE-2021-21267? CVE-2021-21267 has a CVSS score of 7.5 (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 schema-inspector are affected by CVE-2021-21267? schema-inspector (npm) versions < 2.0.0 is affected.
- Is there a fix for CVE-2021-21267? Yes. CVE-2021-21267 is fixed in 2.0.0. Upgrade to this version or later.
- Is CVE-2021-21267 exploitable, and should I be worried? Whether CVE-2021-21267 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-2021-21267 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-2021-21267? Upgrade
schema-inspectorto 2.0.0 or later.