CVE-2021-21267 — schema-inspector
HIGHCVE-2021-21267 is a high-severity (CVSS 7.5) Improper Input Validation vulnerability in schema-inspector. 3 public exploit references exist, so weaponization risk is real. A fix is available for schema-inspector — see the affected versions and patch details below.
Regular Expression Denial-of-Service in npm schema-inspector
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2021-21267 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
schema-inspectornpmDescription
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.
Patches
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.
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | schema-inspector | all versions | 2.0.0npm install schema-inspector@2.0.0 |
Affected Products
e-series performance analyzernetapponcommand insightnetappschema-inspectorschema-inspector_projectResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for schema-inspector, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update schema-inspector to 2.0.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-21267 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.
Frequently Asked Questions
Is CVE-2021-21267 in your dependencies?
Find it across npm, including transitive dependencies.