CVE-2026-34480: Apache Log4j Core invalid XML output in XmlLayout

CVE-2026-34480 · Severity: high · CVSS 7.5 · Published 2026-04-10

Apache Log4j Core, a widely used logging library for Java applications, contains a flaw in how it handles certain characters when generating XML logs. If a log message contains specific forbidden characters, it can cause log data to be silently lost or rejected by downstream monitoring systems. This could lead to gaps in audit trails or operational visibility, potentially hiding malicious activity or system errors.

Technologies: Apache Software Foundation Log4j Core, Google Cloud Platform, org.apache.logging.log4j:log4j-core (Maven). Vendors: Apache Software Foundation, Google, Maven.

Quick answers

Is CVE-2026-34480 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-34480 being exploited in the wild.
How severe is CVE-2026-34480?
High severity, with a CVSS score of 7.5, published 10 April 2026.
Which products and versions are affected?
Apache Software Foundation Log4j Core >= 2.0-alpha1, < 2.25.4; >= 3.0.0-alpha1, <= 3.0.0-beta3; org.apache.logging.log4j:log4j-core (Maven) ECOSYSTEM:introduced=2.0-alpha1,fixed=2.25.4.
Is there a fix for CVE-2026-34480?
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-2026-34480 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-34480?
Check whether you run Apache Software Foundation Log4j Core, Google Cloud Platform or 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
    # set org.apache.logging.log4j:log4j-core to 2.25.4 in your pom.xml or build.gradle

Technical details

The vulnerability exists in the XmlLayout component of Apache Log4j Core due to improper encoding of XML 1.0 forbidden characters (CWE-116). When log messages or Mapped Diagnostic Context (MDC) values contain these characters, the resulting XML is malformed. Depending on the StAX implementation used, this either results in downstream parsers rejecting the log file as a fatal error (JRE built-in StAX) or an exception being thrown during the logging call itself, preventing the event from reaching its appender (Alternative StAX like Woodstox). This is reachable via any network-facing application that logs attacker-controlled input using XmlLayout. The issue is fixed in version 2.25.4.

Affected products

  • Apache Log4j Core >= 2.0-alpha1, < 2.25.4; >= 3.0.0-alpha1, <= 3.0.0-beta3

Identifiers

  • CVE-2026-34480
  • GHSA-3pxv-7cmr-fjr4

Timeline

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

References

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