When you browse public vulnerability databases such as NVD or MITRE CVE, you'll often encounter identifiers like CVE-2021-33121. Usually, these describe security bugs, the vulnerable software, how it can be exploited, and any existing patches or mitigations. But sometimes, you’ll find a CVE marked as “REJECTED” with a reason like “This is unused.” What does that mean, and why does it matter? In this post, we’ll explore the exclusive story behind CVE-2021-33121, using plain language, and explain why its rejection is significant for both researchers and everyday users.

Reason: This is unused.

When you look up CVE-2021-33121 on MITRE or NVD, you’ll see almost no details other than these words:
> "REJECT This candidate has been rejected by its CNA. Further details and reason for rejection can be found here. Reason: This is unused."

The CVE Lifecycle

When a researcher or company suspects a vulnerability, they request a CVE (Common Vulnerabilities and Exposures) number from one of the authorized bodies, called CNAs (CVE Numbering Authorities). However, not all CVEs lead to published vulnerabilities.

The CVE slot was reserved but never used.

For CVE-2021-33121, the reason is clear:
"This is unused."
That means the CVE identifier was reserved for a potential bug, but no vulnerability details were published, and the CNA decided to officially close it as “not used.”

What Does “REJECTED” Mean for Security?

Rejected CVEs are important for preventing rumors, guesswork, or confusion about possible "hidden" bugs. It officially tells the world:
> “There’s no vulnerability here. You don't have to patch or worry about this CVE.”

Suppose you’re building a script that aggregates CVEs for your software

import requests

def is_cve_rejected(cve_id):
    url = f"https://cve.circl.lu/api/cve/{cve_id}";
    resp = requests.get(url)
    data = resp.json()
    return 'REJECT' in data.get('summary', '') or data.get('summary', '') == 'This is unused.'

# Example usage
cve = "CVE-2021-33121"
if is_cve_rejected(cve):
    print(f"{cve} is REJECTED or UNUSED. No action needed.")
else:
    print(f"{cve} may be active. Investigate further.")

Note: Always double-check the status on official sources like MITRE or NVD.

Do Not Be Fooled by Filler or Rumor

Some vendors or scanning tools might flag REJECTED CVEs due to outdated feeds. Always consult the official CVE metadata to avoid unnecessary alarm or confusion.

A Practical Example

> *"We found CVE-2021-33121 in our last security scan. Should we panic?"*

Answer:
No need to panic! CVE-2021-33121 is explicitly marked as REJECTED—there is no published vulnerability, exploit, or patch, and there’s no risk.

- MITRE CVE-2021-33121 Official Page
- NVD CVE-2021-33121 Listing
- How CVEs are Handled and Reserved
- CVE Rejection Policies (MITRE)

In Summary

CVE-2021-33121 is a classic example of a REJECTED, unused CVE.
There’s no exploit, no bug, and no concern for users or IT teams.
Pay close attention to CVE statuses so you can focus your security efforts on real threats.

Stay informed, and share this post with anyone puzzled by rejected CVEs in their reports!

Timeline

Published on: 02/23/2024 21:15:08 UTC
Last modified on: 02/26/2025 06:26:23 UTC