How severe is CVE-2021-21307?

CVE-2021-21307 has a CVSS score of 9.8/10, rated CRITICAL. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-21307?

Affected package information for CVE-2021-21307 is not yet fully mapped. Check the official advisory links for details.

How do I fix CVE-2021-21307?

No fixed version has been published for CVE-2021-21307 yet. Monitor the advisory for updates, apply mitigations recommended by the vendor, and use O3 Security to track when a fix becomes available in your stack.

Is CVE-2021-21307 actively exploited in the wild?

Yes. There are 3 known exploit references for CVE-2021-21307, including 3 in-the-wild exploitations observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2021-21307?

CVE-2021-21307 has an EPSS (Exploit Prediction Scoring System) score of 92.1%, placing it in the 100th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. A score above 50% indicates significantly elevated exploitation risk — immediate patching is strongly recommended.

What type of vulnerability is CVE-2021-21307?

CVE-2021-21307 is classified as CWE-862 (CWE-862). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

Is there exploit tooling available for CVE-2021-21307?

A Nuclei detection template exists for CVE-2021-21307, meaning automated scanners can fingerprint it. Public exploit tooling significantly increases real-world risk — prioritize patching and ensure detection coverage. Exploit tooling should only ever be used in isolated, authorized testing environments.

When was CVE-2021-21307 published, and has it been updated?

CVE-2021-21307 was published on February 11, 2021 and was last updated on April 11, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

CVE-2021-21307

CRITICAL

Published

Feb 11, 2021

Updated

Apr 11, 2026

Affected

0 pkgs

Patched

None yet

Exploits

3 known

EPSS Exploitation Probability

via FIRST.org ↗

92.1%probability of exploitation in next 30 days

Very High Risk100th percentile0.00%

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Description

Lucee Server is a dynamic, Java based (JSR-223), tag and scripting language used for rapid web application development. In Lucee Admin before versions 5.3.7.47, 5.3.6.68 or 5.3.5.96 there is an unauthenticated remote code exploit. This is fixed in versions 5.3.7.47, 5.3.6.68 or 5.3.5.96. As a workaround, one can block access to the Lucee Administrator.

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

Lucee Server is a dynamic, Java based (JSR-223), tag and scripting langu…

github.comNVDAug 2021

Lucee Server is a dynamic, Java based (JSR-223), tag and scripting langu…

github.comMetasploitAug 2021

Lucee Server is a dynamic, Java based (JSR-223), tag and scripting langu…

packetstormsecurity.comNVDSep 2021

Frequently Asked Questions

O3 Security · Impact-Aware SCA

Is CVE-2021-21307 in your stack?

O3 detects CVE-2021-21307 across dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

Scan my stack How O3 SCA works

CVSS Score

9.8/10

CVSS v3 base score

Vector breakdown

AV:Attack Vector

Network

AC:Attack Complexity

Low

PR:Privileges Required

None

UI:User Interaction

None

S:Scope

Unchanged

C:Confidentiality

High

I:Integrity

High

A:Availability

High

Raw vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CWE Classification

Weaponization

OpenSSF Scorecard

Package health score

Lucee

4.0/10

Code-Review1/10

Maintained10/10

Branch-Protection0/10

Assessed Jun 8, 2026

Timeline

Disclosed

Feb 11, 2021

First exploit

Aug 17, 2021

Last updated

Apr 11, 2026

Identifiers

CVE-2021-21307

References

Advisorydev.lucee.org Advisorygithub.com Advisoryportswigger.net Fixgithub.com Fixciacfug.org Evidencegithub.com Evidencepacketstormsecurity.com

Data from OSV.dev, enriched by O3 Security. Refreshed hourly.