Security vulnerabilities are an everyday reality in the software world. Each year, thousands of CVEs (Common Vulnerabilities and Exposures) are discovered, documented, and publicly disclosed. One such identifier, CVE-2021-21158, briefly caught the attention of the security community — only to be rejected after investigation. But what led to this CVE's rejection? What can we learn from the process? In this post, we'll break down the timeline, technical details, and the reasons behind its exclusion, using plain English. We'll also share some real code snippets and point to the available references.

What Was CVE-2021-21158?

CVE-2021-21158 was a candidate vulnerability report submitted for tracking a potential security issue. Its initial description, according to the NVD (National Vulnerability Database), was:

> "REJECT Reason: Further investigation determines issue is not within scope of this CNA."

REJECT means the CVE was withdrawn, and no further action will happen.

- CNA stands for "CVE Numbering Authority", a trusted group that issues CVEs for specific software.

In short, after deeper research, the authority determined the reported issue was not actually a vulnerability that could be assigned under their scope.

Initial Report: Someone noticed a potential security issue and reported it to a CNA.

2. CVE Reserved: The CNA reserved the CVE-2021-21158 identifier as part of their triage and tracking process.

Further Investigation: Experts examined the report in depth.

4. Rejection: The CNA finally determined the issue didn’t meet their criteria, and officially marked the CVE as REJECTED.

References

- CVE Details - CVE-2021-21158
- NVD Listing for CVE-2021-21158

If you look up CVE-2021-21158, you’ll see this statement across all major CVE trackers

> "REJECT Reason: Further investigation determines issue is not within scope of this CNA."

What does “not within scope of this CNA” mean?

- The authority (CNA) responsible for tracking vulnerabilities for a certain vendor or product did not consider the issue to be a security bug affecting their product.
- Sometimes, the reported flaw might be a natural behavior, a configuration issue, or simply not risky in real-world use.

Example of a Non-Scoping Issue

Let’s say someone files a bug about a feature in a web browser that allows users to copy and paste JavaScript from the developer console into a website. After looking closer, the browser security team may decide this is expected and documented feature—not a security vulnerability.

For illustration, here’s a simple (pretend) code snippet that might look “suspicious”

// In the browser console
document.cookie = "session=attacker";

- Is this a vulnerability? Not necessarily. The developer console is supposed to let you change things for testing. If a user pastes code here, that’s their own choice.
- Many CVEs get rejected if the “exploit” turns out to require this kind of intentional user action.

The REJECT Process: How Does It Work?

When a reported issue is rejected, the CVE entry is updated with the “REJECT” status. It stays in the database for transparency but is marked as invalid. Here’s what happens:

The original report is reviewed by the CNA.

- If it doesn’t fit their criteria — for example, it’s not a real bug, or it’s not their product — they update the record.

Did Anyone Exploit CVE-2021-21158?

No. Since the CVE was never turned into a real vulnerability with technical details or risk of attack, no exploits were published.

A reminder: People sometimes look up CVE numbers expecting to find hacking tools or exploit scripts, but “REJECT” status means no real exploit exists — this is just a tracking number, not an active threat.

Let’s say you find suspicious code

// Example of potentially risky code
userInput = "<script>alert('XSS');</script>"
document.getElementById('output').innerHTML = userInput;

If it’s used in a public website, that’s a real XSS (Cross-Site Scripting) issue.

- But if this code is *only* run by a developer or in a non-production environment, some organizations may choose not to issue a CVE.

This is how some reports get rejected: context matters.

Rejected CVEs Make a Healthy System

- Public rejections show that the process is transparent — better to reject than to hide false reports!

If you see a rejected CVE in your scan reports, double-check the status. REJECT means you’re safe.

## Further Reading / References

- NVD: CVE-2021-21158
- CVE Entry at cve.org
- How CVE IDs are Assigned
- Rejected CVEs Explained

Conclusion

CVE-2021-21158 is a great case study in how the public process works: not every security report turns out to be a real threat, and industry authorities handle these situations with care. So if you see this CVE pop up in your security dashboard, you can rest easy — it’s officially a non-issue. Remember: always verify CVEs before taking action!

*P.S. Want to learn more about real vulnerabilities? Always check the “status” and read the official notes before panicking about any CVE you see in the wild.*

Timeline

Published on: 01/17/2025 23:15:12 UTC