JMSAppender in Log4j 1.2 is vulnerable to deserialization of untrusted data

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2021-4104: 80.60% estimated exploitation activity in the next 30 days; percentile 99.63 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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.

Published by the source

14 Dec 2021, 19:49 UTC

Last modified by the source

22 Dec 2023, 15:07 UTC

Source last checked

26 Oct 2026, 16:24 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-fp5r-v3w9-4333

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# Patch Next advisory brief: CVE-2021-4104

Advisory: JMSAppender in Log4j 1.2 is vulnerable to deserialization of untrusted data
IDs: CVE-2021-4104, GHSA-fp5r-v3w9-4333
Record: https://patchnext.com/advisories/cve-2021-4104 (revision 1, source checked 26 Oct 2026, 16:24 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor response not established. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven org.zenframework.z8.dependencies.commons:log4j-1.2.17: affected <= 2.0
- Maven log4j:log4j: affected >= 1.2.0, <= 1.2.17

## Suggested inspection (read-only)
- Maven org.zenframework.z8.dependencies.commons:log4j-1.2.17: check the installed version with your package manager.
- Maven log4j:log4j: check the installed version with your package manager.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on org.zenframework.z8.dependencies.commons:log4j-1.2.17, log4j:log4j.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-fp5r-v3w9-4333 (GitHub-reviewed advisory GHSA-fp5r-v3w9-4333 lists affected ranges: Maven log4j:log4j >=1.2.0 =0 <=2.0)

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