Executive brief
Apache Tomcat, a widely used web server and application container, contains a vulnerability in its JSON logging component. This flaw allows for improper data formatting in access logs, which could lead to the exposure of sensitive information or interfere with log monitoring systems. Organizations using affected versions should upgrade to ensure their application logs remain secure and accurate.
Technical details
An Improper Encoding or Escaping of Output vulnerability (CWE-116) exists in the JsonAccessLogValve component of Apache Tomcat. The vulnerability stems from incomplete escaping of data when generating JSON-formatted access logs. A remote, unauthenticated attacker can exploit this by sending specially crafted requests that, when logged, break the JSON structure or inject unexpected content. This can lead to the disclosure of sensitive information or the manipulation of log data consumed by downstream analysis tools. The issue is resolved in versions 11.0.21, 10.1.54, and 9.0.117.
Affected products
- Apache Tomcat 11.0.0-M1 through 11.0.20, 10.1.0-M1 through 10.1.53, 9.0.40 through 9.0.116, 8.5.84 through 8.5.100
Timeline
- 2026-04-09: disclosed
- 2026-04-09: advisory
- 2026-04-09: patched