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CVE-2021-45046

9, critical Known exploited Used in ransomware

Apache Log4j2 Deserialization of Untrusted Data Vulnerability

NVD (opens in a new tab) CVE.org (opens in a new tab) CISA KEV catalogue (opens in a new tab)
CVSS
9, critical critical CVSS v3.1
EPSS, next 30 days
100% higher than 99.9% of scored CVEs
Exploitation
Confirmed in the wild
Published
14 Dec 20214 years ago

Known exploited

CISA added this to the Known Exploited Vulnerabilities Catalog on 1 May 2023 and links it to ransomware activity. US federal agencies had to remediate by 22 May 2023, a deadline that has passed.

Required action. Apply updates per vendor instructions.

Description

It was found that the fix to address CVE-2021-44228 in Apache Log4j 2.15.0 was incomplete in certain non-default configurations. This could allows attackers with control over Thread Context Map (MDC) input data when the logging configuration uses a non-default Pattern Layout with either a Context Lookup (for example, $${ctx:loginId}) or a Thread Context Map pattern (%X, %mdc, or %MDC) to craft malicious input data using a JNDI Lookup pattern resulting in an information leak and remote code execution in some environments and local code execution in all environments. Log4j 2.16.0 (Java 8) and 2.12.2 (Java 7) fix this issue by removing support for message lookup patterns and disabling JNDI functionality by default.

Details

Vendor
Apache
Product
Apache Log4j
Weakness
CWE-917 (opens in a new tab)
Status
Analyzed
Updated
17 Jun 2026
Assigner
security@apache.org

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

References 22

Patches and fixes 1

Advisories 17

9 more

Other references 4

The kind is read from NVD's tags where present and from the shape of the URL otherwise, so treat it as a hint.

Other Apache CVEs

Every Apache CVE we hold

Same vendor in what we hold, not a known link between the flaws.

  • CVE-2026-34486 Apache Tomcat Missing Encryption of Sensitive Data Vulnerability KEV EPSS 7% 7.5, high
  • CVE-2026-34197 Apache ActiveMQ Improper Input Validation Vulnerability KEV EPSS 15% 8.8, high
  • CVE-2025-24813 Apache Tomcat Path Equivalence Vulnerability KEV EPSS 100% 9.8, critical
  • CVE-2024-45195 Apache OFBiz Forced Browsing Vulnerability KEV EPSS 100% 7.5, high
  • CVE-2024-38856 Apache OFBiz Incorrect Authorization Vulnerability KEV EPSS 99% 9.8, critical
  • CVE-2024-38475 Apache HTTP Server Improper Escaping of Output Vulnerability KEV EPSS 100% 9.1, critical
  • CVE-2024-32113 Apache OFBiz Path Traversal Vulnerability KEV EPSS 100% 9.8, critical
  • CVE-2024-27348 Apache HugeGraph-Server Improper Access Control Vulnerability KEV EPSS 99% 9.8, critical

Beyond this page

Is CVE-2021-45046 in your network?

This page tells you how dangerous CVE-2021-45046 is out there. Whether it sits on one of your devices, only a scan of your own network can tell. That is what our systems do, every day, for the companies we protect.

CVE-2021-45046 is in the CISA catalogue of exploited vulnerabilities: attackers are already exploiting it.

  • EXYS7600 OCELOT

    Find it before attackers do

    Ocelot scans your network on a schedule and reports every vulnerability it finds by its CVE identifier, with its CVSS score and how many of your hosts are affected. A finding like CVE-2021-45046 comes with the devices to patch.

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  • EXYS7950 KONDRA

    Detect it if it's exploited

    Until the patch is applied, Kondra monitors your network, events and endpoints in real time. It keeps an inventory of the software installed on every endpoint, and its anomaly detection rules flag what an attacker does once inside.

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Check your exposure

Assembled from the NVD 2.0 API, the CISA Known Exploited Vulnerabilities Catalog and FIRST EPSS. Scores are as of our last collection on 17 Oct 2026, not the live upstream state.