Apache

CVE-2021-4104: Deserialization of untrusted data in JMSAppender in Apache Log4j 1.2

Is it exploited?

Reported, not confirmed by CISA. VulnCheck KEV lists it as exploited in the wild. CISA has not added it to its Known Exploited Vulnerabilities catalog as of 29 Oct 2026.

VulnCheck KEV lists it since 26 Apr 2022. It cites 3 public reports, the first from 26 Apr 2022.

How likely is exploitation in the next 30 days?

80.6%

EPSS score, percentile 99.6 of all scored records. A probability estimated by FIRST, not a report of exploitation.

How severe?

7.5 High

CVSS v3.1 base score, from CISA's enrichment of the record

What should I do?

CISA has set no required action, because the vulnerability is not in KEV.

Advisories and patches (4)

Which versions are affected?

Affected

Apache Log4j 1.2 1.2.x

Versions by product

Source: CISA KEV 2026.10.29, as of 29 Oct 2026; VulnCheck KEV, as of 30 Oct 2026; FIRST EPSS, as of 29 Oct 2026; CVE List, as of 30 Oct 2026. About the data.

Description

Deserialization of untrusted data in JMSAppender in Apache Log4j 1.2

JMSAppender in Log4j 1.2 is vulnerable to deserialization of untrusted data when the attacker has write access to the Log4j configuration. The attacker can provide TopicBindingName and TopicConnectionFactoryBindingName configurations causing JMSAppender to perform JNDI requests that result in remote code execution in a similar fashion to CVE-2021-44228. Note this issue only affects Log4j 1.2 when specifically configured to use JMSAppender, which is not the default. Apache Log4j 1.2 reached end of life in August 2015. Users should upgrade to Log4j 2 as it addresses numerous other issues from the previous versions.

Source: CVE List, as of 30 Oct 2026. About the data.

What to do

Advisories and patches

GLSA-202209-02 (Vendor advisory)
GLSA-202310-16 (Vendor advisory)
GLSA-202312-02 (Vendor advisory)
GLSA-202312-04 (Vendor advisory)

This summary is based on the CVE record as of 30 Oct 2026. Check the vendor's advisory before you act: affected versions and fixes can change.

Affected products and versions

Versions by product, as listed in the CVE record (1 product)

Apache Software Foundation Apache Log4j 1.x
Status	Versions
Affected	Apache Log4j 1.2 1.2.x

Source: CVE List, as of 30 Oct 2026. About the data.

Weakness

CWE-502

CWE-502: Deserialization of Untrusted Data

CWE and CAPEC are maintained by MITRE; the entries are those named in the CVE record.

Timeline

Date	Event
14 Dec 2021	CVE record published
28 May 2026	CVE record last updated

References

2 more in the CVE record.

Known exploited Apache vulnerabilities

CVE-2016-3081: Apache Struts Command Injection Vulnerability (added 8 Oct 2026)
CVE-2026-34486: Apache Tomcat Missing Encryption of Sensitive Data Vulnerability (added 4 Aug 2026)
CVE-2026-34197: Apache ActiveMQ Improper Input Validation Vulnerability (added 16 Apr 2026)
CVE-2024-38475: Apache HTTP Server Improper Escaping of Output Vulnerability (added 1 May 2025)
CVE-2025-24813: Apache Tomcat Path Equivalence Vulnerability (added 1 Apr 2025)