Vulnerability report

Exploitation attempts observed Confirmed confidence Not in CISA KEV

CVE-2021-21307

Remote Code Exploit in Lucee Admin

Lucee · >= 5.3.5.0, < 5.3.5.96

Watch CVE-2021-21307 Browse KEV feed
Severity
CVSS 8.6 · High
Confidence
Confirmed
Exploit status
Observed in sensors
EPSS
89.2%
First observed
09 Sep 2026
Last observed
19 Oct 2026

Decision summary

What security teams need to know first

Direct answers before the deeper technical record.

What it is

CVE-2021-21307 is an unauthenticated Remote Code Exploit in Lucee Admin. Lucee Server is a dynamic, Java based (JSR-223), tag and scripting language used for rapid web application development. In Lucee Admin before...

Have exploitation attempts been observed?

Yes. Previdian sensors observed exploitation attempts targeting this vulnerability. Also reported by third-party sources. Confidence is confirmed.

Who is affected?

Lucee >= 5.3.5.0, < 5.3.5.96.

What should we do?

Patch immediately, validate internet-facing exposure, and monitor for matching requests.

Overview

Lucee Server is a dynamic, Java based (JSR-223), tag and scripting language used for rapid web application development

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.

lucee Affected
Lucee
>= 5.3.5.0, < 5.3.5.96 >= 5.3.6.0, < 5.3.6.68 >= 5.3.7.0, < 5.3.7.47
Published
11 Feb 2021
Exploitation Attempts Reported
22 Apr 2025
Attack vector
Remote
Complexity
Low
Privileges
None
User interaction
None

Tags

nuclei_scanner metasploit java metasploit_scanner

CVE References

Exploitation evidence

Evidence of exploitation attempts

Third-party attestation and first-party sensor observation are shown separately so teams can judge the evidence chain.

Exploitation attempts observed in the wild

The Shadowserver

Recorded 22 Apr 2025

A trusted third party reported exploitation attempts.

Exploitation attempts observed

Previdian sensor

First observed 09 Sep 2026

Previdian sensors observed exploitation attempts targeting this vulnerability.

Proof of concept available

Nuclei Templates

Recorded 28 Apr 2025

Public scanner or PoC coverage increases practical exploitability.

Known exploited vulnerability sources

Per-source evidence links for KEV attestations are available through the Previdian Pro API.

Learn about Pro API access
Source Added
The Shadowserver First 2025-04-22 00:00 UTC
Previdian Sensors 2026-10-19 22:17 UTC

Operational indicators for this CVE are listed under Detection.

Sensor telemetry

First-party evidence of exploitation activity

Previdian sensors recorded exploitation attempts targeting this vulnerability. The cards and chart show volume, unique attackers, and daily activity.

8

Attempts observed

7

Unique attacker IPs

5

Attacker countries

CH · FR · JP · US · YE

7

Sensors observed

CVE-2021-21307 exploitation attempts over the last 48 days

Daily events observed by Previdian sensors

Updated 25 Oct 2026

0
1
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0
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0
0
0
0
1
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0
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0
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2
1
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0
8 Sep 18 Sep 28 Sep 8 Oct 25 Oct

First observed 09 Sep 2026 · Last observed 19 Oct 2026

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Detection

Operational artifacts and observed signals

Make the evidence actionable in scanner, SOC, and edge-control workflows.

Observed signals

Request targets
User-Agents
Callback hosts
4
5
0

Request targets and User-Agents available in Pro. Callback host details available in Enterprise.

Virtual patch status

No Previdian virtual patch is currently available. Future rules ship for ModSecurity, Cloudflare, and AWS WAF.

Learn about virtual patches →

Attacker IP Indicators

Attacker IP indicators observed · available in Pro and Enterprise.

Sensor-derived attacker IP indicators are available to Pro and Enterprise accounts under Detection and through the Pro API.

Learn about Pro API access

Scanner Artifacts

Scanner and exploit-framework references linked to this CVE.

Scanner Reference Detected
Metasploit https://github.com/rapid7/metasploit-framework/blob/master/modules/exploits/linux/http/lucee_admin_imgprocess_file_write.rb 28 Apr 2025
Nuclei https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2021/CVE-2021-21307.yaml 25 Apr 2025

Risk and context

Severity, weaknesses, and research context

CVSS v3.1

8.6 High

Potential damage if exploited. Separate from whether attackers are using it.

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

EPSS

89.2%

Estimated chance of exploitation in the next 30 days. Previdian's warning comes from evidence, not this score.

Weaknesses

Missing Authorization CWE-862

All CVSS Scores

CVSS v3.1 8.6 High

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

CVSS v2.0 7.5 High

AV:N/AC:L/Au:N/C:P/I:P/A:P

Potential Proof of Concepts

These PoCs are unverified and could contain malware. Use at your own risk.

Lucee Admin - Remote Code Execution

nuclei · Created Unknown

lucee_admin_imgprocess_file_write

metasploit · Created Unknown

Metasploit module for CVE-2021-21307

Timeline

From disclosure to observed exploitation attempts

  1. 07:57 UTC

    Indicators of compromise added (7)

    Indicators of compromise recorded

  2. 07:57 UTC

    Observed by Previdian sensors

    Previdian sensors observed exploitation attempts targeting this vulnerability.

  3. 15:02 UTC

    Metasploit module available

    Exploit module available

  4. 15:02 UTC

    Public PoC available

    Public proof-of-concept code published

  5. 00:00 UTC

    Nuclei template available

    Scanner coverage available

  6. 00:00 UTC

    Added to Previdian KEV Feed

    High-confidence, third-party report of exploitation attempts

  7. 18:20 UTC

    CVE published

    Vulnerability disclosed publicly

  8. 00:00 UTC

    CVE ID reserved

    Identifier reserved by the CNA

Pro API

Automate this intelligence

Confidence, exploit status, sensor telemetry, PoCs, scanner integrations, mentions, and tags are available programmatically for VM, SOC, and CTI workflows.

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  • Evidence confidence and provenance
  • First-party sensor telemetry
  • PoC and scanner references
  • Affected versions and enrichment
  • Automation-ready JSON delivery

GET /api/v2/pro/kevs/CVE-2021-21307

Sample API response 
{
  "cve_id": "CVE-2021-21307",
  "confidence": "Confirmed",
  "cvss_score": 8.6,
  "cvss_estimated": false,
  "epss_score": 0.89189,
  "exploit_status": {
    "exploited_in_the_wild": true,
    "active_exploitation_observed": true
  },
  "sensor_telemetry": { "attempts": 8, "sensors": 7 }
}