# CVE-2026-34477: Apache Log4j Core improper certificate validation in network appenders

Source: https://junglewise.ai/threats/cve-2026-34477-apache-log4j-core-improper-certificate-validation-in-network  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-04-10. Updated: 2026-05-10  
License: CC BY 4.0 with a link back

CVE-2026-34477 · Severity: medium · CVSS 5.9 · Published 2026-04-10

Apache Log4j is a widely used logging library for Java applications. A security flaw exists where certain encrypted connections (TLS) fail to verify the identity of the server they are connecting to, even when configured to do so. This could allow a sophisticated attacker on the same network to intercept or modify log data being sent to remote servers, potentially exposing sensitive system information or operational logs.

Technologies: [org.apache.logging.log4j:log4j-core (Maven)](https://junglewise.ai/threats/technologies/org-apache-logging-log4j-log4j-core). Vendors: [Maven](https://junglewise.ai/threats/vendors/maven).

## Quick answers

**Is CVE-2026-34477 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-34477 being exploited in the wild.

**How severe is CVE-2026-34477?** Medium severity, with a CVSS score of 5.9, published 10 April 2026.

**Which products and versions are affected?** org.apache.logging.log4j:log4j-core (Maven) ECOSYSTEM:introduced=2.12.0,fixed=2.25.4.

**Is there a fix for CVE-2026-34477?** Yes. org.apache.logging.log4j:log4j-core (Maven): upgrade to 2.25.4 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-34477 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-34477?** Check whether you run org.apache.logging.log4j:log4j-core (Maven) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- org.apache.logging.log4j:log4j-core (Maven): upgrade to 2.25.4 or later

  ```sh
  # set org.apache.logging.log4j:log4j-core to 2.25.4 in your pom.xml or build.gradle
  ```


## Technical details

Apache Log4j Core contains a vulnerability (CWE-297) where the 'verifyHostName' attribute within the <Ssl> configuration element is silently ignored. This flaw affects SMTP, Socket, and Syslog appenders when TLS is configured via nested <Ssl> elements. A network-based attacker can perform a man-in-the-middle (MitM) attack if they can present a certificate issued by a trusted Certificate Authority. This issue is an incomplete fix for a previous vulnerability and does not affect the HTTP appender. Users should upgrade to version 2.25.4 to ensure hostname verification is correctly enforced.

## Affected products

- Apache Log4j Core >= 2.12.0, < 2.25.4; >= 3.0.0-alpha1, <= 3.0.0-beta3

## Identifiers

- CVE-2026-34477
- GHSA-6hg6-v5c8-fphq

## Timeline

- 2026-04-10: advisory: Original advisory published by GitHub and NVD
- 2026-04-14: other: Advisory reviewed and updated

## References

- [https://api.github.com/users/ppkarwasz](https://api.github.com/users/ppkarwasz)
- [https://github.com/ppkarwasz](https://github.com/ppkarwasz)
- [https://api.github.com/users/ppkarwasz/gists%7B/gist_id%7D](https://api.github.com/users/ppkarwasz/gists%7B/gist_id%7D)
- [https://api.github.com/users/ppkarwasz/repos](https://api.github.com/users/ppkarwasz/repos)
- [https://avatars.githubusercontent.com/u/12533274?v=4](https://avatars.githubusercontent.com/u/12533274?v=4)
- [https://api.github.com/users/ppkarwasz/events%7B/privacy%7D](https://api.github.com/users/ppkarwasz/events%7B/privacy%7D)

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- [Apache Log4j does not verify the TLS hostname in its Socket Appender](https://junglewise.ai/threats/cve-2025-68161-apache-log4j-does-not-verify-the-tls-hostname-in-its-socket)
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- [Apache Log4j2 remote code execution via JDBC Appender JNDI injection](https://junglewise.ai/threats/cve-2021-44832-apache-log4j2-remote-code-execution-via-jdbc-appender-jndi)