# CVE-2026-34478: Apache Log4j Core log injection in Rfc5424Layout

Source: https://junglewise.ai/threats/cve-2026-34478-apache-log4j-core-log-injection-in-rfc5424layout  
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-2026-34478 · Severity: high · CVSS 7.5 · Published 2026-04-10

Apache Log4j Core, a widely used logging library for Java applications, contains a flaw that can allow attackers to inject malicious entries into system logs. This occurs because certain security settings were accidentally disabled during a software update, potentially allowing attackers to hide their activities or spoof log data. Organizations using specific syslog configurations should update to ensure their audit logs remain accurate and secure.

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-2026-34478 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-34478 being exploited in the wild.

**How severe is CVE-2026-34478?** High severity, with a CVSS score of 7.5, published 10 April 2026.

**Which products and versions are affected?** org.apache.logging.log4j:log4j-core (Maven) ECOSYSTEM:introduced=2.21.0,fixed=2.25.4.

**Is there a fix for CVE-2026-34478?** 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-2026-34478 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-34478?** 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's Rfc5424Layout component is vulnerable to log injection via CRLF sequences. The vulnerability stems from the undocumented renaming of two configuration attributes: 'newLineEscape' and 'useTlsMessageFormat'. When users configure Rfc5424Layout directly, the 'newLineEscape' rename causes newline escaping to fail for TCP framing (RFC 6587), while the 'useTlsMessageFormat' rename causes a silent downgrade from TLS framing (RFC 5425) to unframed TCP without escaping. Attackers can exploit this via the network to inject arbitrary log entries. Users of SyslogAppender are unaffected. A fix is available in version 2.25.4.

## Affected products

- Apache Log4j Core >= 2.21.0, < 2.25.4; >= 3.0.0-beta1, <= 3.0.0-beta3

## Identifiers

- CVE-2026-34478
- GHSA-445c-vh5m-36rj

## Timeline

- 2026-04-10: disclosed
- 2026-04-10: advisory
- 2026-04-10: patched: Fixed in version 2.25.4

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- [https://api.github.com/users/ppkarwasz/events%7B/privacy%7D](https://api.github.com/users/ppkarwasz/events%7B/privacy%7D)

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