Vulnerability report

Active exploitation observed Confirmed confidence In CISA KEV

CVE-2021-44228

Apache Log4j2

Apache Log4j2 · affected before log4j-core*

Watch CVE-2021-44228 Browse KEV feed
Severity
CVSS 10.0 · Critical
Confidence
Confirmed
Exploit status
Observed in sensors
EPSS
100.0%
First observed
03 Jul 2026
Last observed
08 Oct 2026

Decision summary

What security teams need to know first

Direct answers before the deeper technical record.

What it is

CVE-2021-44228 is an unauthenticated vulnerability affecting Apache Log4j2. Apache Log4j2 2.0-beta9 through 2.15.0 (excluding security releases 2.12.2, 2.12.3, and 2.3.1) JNDI features used in configuration, log...

Is it exploited?

Yes. Previdian sensors observed exploitation attempts with confirmed confidence. Listed in CISA KEV. Also confirmed by third-party sources.

Who is affected?

Apache Log4j2 affected before log4j-core*.

What should we do?

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

Overview

Apache Log4j2

Apache Log4j2 2.0-beta9 through 2.15.0 (excluding security releases 2.12.2, 2.12.3, and 2.3.1) JNDI features used in configuration, log messages, and parameters do not protect against attacker controlled LDAP and other JNDI related endpoints. An attacker who can control log messages or log message parameters can execute arbitrary code loaded from LDAP servers when message lookup substitution is enabled. From log4j 2.15.0, this behavior has been disabled by default.

From version 2.16.0 (along with 2.12.2, 2.12.3, and 2.3.1), this functionality has been completely removed. Note that this vulnerability is specific to log4j-core and does not affect log4net, log4cxx, or other Apache Logging Services projects.

Apache Software Foundation Affected
Apache Log4j2
Before log4j-core*
View vendor advisory (opens in new tab)
Published
10 Dec 2021
Exploitation Reported
10 Dec 2021
Attack vector
Remote
Complexity
Low
Privileges
None
User interaction
None

Tags

ransomware apache malware metasploit nuclei_scanner cisa

CVE References

Exploitation evidence

Why Previdian marks this CVE as exploited

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

Exploited in the wild

CISA

Recorded 10 Dec 2021

A trusted third party reported exploitation.

Active exploitation observed

Previdian sensor

First observed 28 Jul 2026

Previdian first observed exploitation attempts targeting this vulnerability in our honeypot sensors.

Used in malware

CISA

Recorded 10 Dec 2021

Malware families have been linked to exploitation of this CVE.

Proof of concept available

GitHub

Recorded 09 Dec 2021

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
CISA First 2021-12-10 00:00 UTC
The Shadowserver 2026-06-01 00:00 UTC
Tenable Blog 2026-06-02 14:21 UTC
Previdian Sensors 2026-08-26 15:09 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.

1,828

Attempts observed

92

Unique attacker IPs

13

Attacker countries

BG · CA · CH · DE · FI · FR · IN · JP · KR · NL · NO · SI · US

26

Sensors observed

CVE-2021-44228 exploitation attempts over the last 80 days

Daily events observed by Previdian sensors

Updated 09 Oct 2026

0
6
0
0
0
0
9
8
76
8
8
4
185
62
4
9
50
26
8
4
20
20
16
14
8
8
8
8
20
45
0
4
8
300
102
8
0
8
26
24
8
8
1
8
8
8
8
8
20
33
28
4
28
28
8
18
8
24
8
12
8
32
56
94
0
20
16
22
24
20
10
25
18
24
13
16
6
16
18
0
22 Jul 7 Aug 23 Aug 8 Sep 9 Oct

First observed 03 Jul 2026 · Last observed 08 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
597
267
1

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/multi/http/vmware_vcenter_log4shell.rb 29 Apr 2025
Nuclei https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2021/CVE-2021-44228.yaml 25 Apr 2025

Risk and context

Severity, weaknesses, and research context

CVSS v3.1

10.0 Critical

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:H/I:H/A:H

EPSS

100.0%

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

Weaknesses

Improper Input Validation CWE-20 Uncontrolled Resource Consumption CWE-400 Deserialization of Untrusted Data CWE-502 Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection') CWE-917

Recent mention · Huntress Blog

Culture at Speed: Protecting What Makes Huntress Work

As Huntress scales past 800 teammates, Chief People Officer Kristin Dean reflects on protecting culture and not just letting it happen.

Read full advisory

All CVSS Scores

CVSS v3.1 10.0 Critical

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

CVSS v2.0 9.3 High

AV:N/AC:M/Au:N/C:C/I:C/A:C

All Mentions

Recent mention · Huntress Blog

Culture at Speed: Protecting What Makes Huntress Work

Huntress Blog · 25 Sep 2026

As Huntress scales past 800 teammates, Chief People Officer Kristin Dean reflects on protecting culture and not just letting it happen.

Recent mention · PaperCut Security Bulletins

PaperCut NG/MF Security Bulletin (March 2022)

PaperCut Security Bulletins · 05 Sep 2026

PaperCut NG/MF Security Bulletin (March 2022) THE PAGE APPLIES TO: collapseMenuSize" id="toc-container" class="toc" :class="tocFullyScrolled ? 'toc--bottom' : 'toc--scrolling'" aria-label="Table of Contents"> Contents Overview Product Status FAQs Contents Overview Product Status FAQs This page was originally titled PaperCut NG/MF RCE (PC-18750), and has been renamed to reflect our current naming convention for Security Bulletins.We have received a vulnerability report for a high severity security issue in PaperCut MF/NG from version 19.2.1 through to the 21.2.8 release. This high severity...

Recent mention · PaperCut Security Bulletins

Spring4Shell (CVE-2022–22965)

PaperCut Security Bulletins · 05 Sep 2026

Spring4Shell (CVE-2022–22965) THE PAGE APPLIES TO: collapseMenuSize" id="toc-container" class="toc" :class="tocFullyScrolled ? 'toc--bottom' : 'toc--scrolling'" aria-label="Table of Contents"> Contents Overview Product Status FAQs References Contents Overview Product Status FAQs References This critical vulnerability was disclosed on the 30th March 2022 and impacts the Spring framework (3rd party framework that we use within PaperCut MF and NG from version 20.0.0). This vulnerability is commonly referred to as Spring4Shell or SpringShell. More information can be found on the Spring blog...

Recent mention · Tenable Blog

Inside the customer environment: Where threat actors, vulnerabilities, and exposed assets intersect

Tenable Blog · 27 May 2026

Tenable Research has developed a graph-based model linking 600+ threat groups to real-world customer exposures. It reveals which vulnerabilities sit at the intersection of severity, active exploitation, and organizational risk.Key takeawaysThe "patch everything" strategy is dead: Vulnerability prioritization based on exploitation risk offers a path forward. A directed graph model linking 600+ threat actors to vulnerabilities in 7,800 customer environments reveals that 68% of organizations carry at least one CVE previously exploited by a named adversary, and 321 tracked threat groups can...

Potential Proof of Concepts

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

CERTCC/CVE-2021-44228_scanner

github · Created 2021-12-14 23:33:51 UTC · 346 stars · AI assessment 90%

Scanners for Jar files that may be vulnerable to CVE-2021-44228

logpresso/CVE-2021-44228-Scanner

github · Created 2021-12-11 11:18:46 UTC · 857 stars · AI assessment 90%

Vulnerability scanner and mitigation patch for Log4j2 CVE-2021-44228

Puliczek/CVE-2021-44228-PoC-log4j-bypass-words

github · Created 2021-12-10 22:35:00 UTC · 938 stars · AI assessment 90%

🐱‍💻 ✂️ 🤬 CVE-2021-44228 - LOG4J Java exploit - WAF bypass tricks

jas502n/Log4j2-CVE-2021-44228

github · Created 2021-12-10 05:23:44 UTC · 464 stars · AI assessment 90%

Remote Code Injection In Log4j

tangxiaofeng7/CVE-2021-44228-Apache-Log4j-Rce

github · Created 2021-12-09 15:27:38 UTC · 82 stars · AI assessment 90%

Apache Log4j 远程代码执行

Apache Log4j2 Remote Code Injection

nuclei · Created Unknown

vmware_vcenter_log4shell

metasploit · Created Unknown

Metasploit module for CVE-2021-44228

ubiquiti_unifi_log4shell

metasploit · Created Unknown

Metasploit module for CVE-2021-44228

log4shell_header_injection

metasploit · Created Unknown

Metasploit module for CVE-2021-44228

mobileiron_core_log4shell

metasploit · Created Unknown

Metasploit module for CVE-2021-44228

Timeline

From disclosure to observed exploitation

  1. 02:37 UTC

    Observed by Previdian sensors

    Evidence-backed exploitation signal

  2. 04:32 UTC

    Indicators of compromise added (93)

    Indicators of compromise recorded

  3. 14:21 UTC

    KEV confirmed by Tenable Blog

    Exploitation attested by an external source

  4. 00:00 UTC

    KEV confirmed by The Shadowserver

    Exploitation attested by an external source

  5. 10:58 UTC

    Metasploit module available

    Exploit module available

  6. 00:00 UTC

    Nuclei template available

    Scanner coverage available

  7. 00:00 UTC

    Added to CISA KEV

    Listed in the CISA Known Exploited Vulnerabilities catalog

  8. 00:00 UTC

    First public exploitation report

    Exploit observed in malware

  9. 00:00 UTC

    CVE published

    Vulnerability disclosed publicly

  10. 15:27 UTC

    Public PoC available

    Public proof-of-concept code published

  11. 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-2021-44228

Free JSON includes basic KEV fields 
{
  "cve_id": "CVE-2021-44228",
  "confidence": "Confirmed",
  "cvss_score": 10.0,
  "cvss_estimated": false,
  "epss_score": 0.99999,
  "exploit_status": {
    "exploited_in_the_wild": true,
    "active_exploitation_observed": true
  },
  "sensor_telemetry": { "attempts": 1828, "sensors": 26 }
}