CVE-2026-34483
Published: 09 April 2026
Summary
CVE-2026-34483 is a high-severity Improper Encoding or Escaping of Output (CWE-116) vulnerability in Apache Tomcat. Its CVSS base score is 7.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 23.8th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 SI-15 (Information Output Filtering) and SI-2 (Flaw Remediation).
Threat & Defense at a Glance
Threat & Defense Details
Mitigating Controls (NIST 800-53 r5)AI
Directly remediates the improper encoding vulnerability in Apache Tomcat's JsonAccessLogValve through timely application of vendor patches and upgrades.
Mandates filtering and proper encoding of output information, countering the CWE-116 improper escaping in JSON access log output that enables sensitive data disclosure.
Protects audit records generated by JsonAccessLogValve from unauthorized access and disclosure, mitigating exploitation of the encoding flaw.
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
The CVE describes a remote unauthenticated network-accessible vulnerability in the public-facing JsonAccessLogValve of Apache Tomcat that directly enables exploitation for sensitive information disclosure.
NVD Description
Improper Encoding or Escaping of Output vulnerability in the JsonAccessLogValve component of Apache Tomcat. This issue affects Apache Tomcat: from 11.0.0-M1 through 11.0.20, from 10.1.0-M1 through 10.1.53, from 9.0.40 through 9.0.116. Users are recommended to upgrade to version 11.0.21, 10.1.54…
more
or 9.0.117 , which fix the issue.
Deeper analysisAI
CVE-2026-34483 is an Improper Encoding or Escaping of Output vulnerability (CWE-116) in the JsonAccessLogValve component of Apache Tomcat. It affects Apache Tomcat versions from 11.0.0-M1 through 11.0.20, 10.1.0-M1 through 10.1.53, and 9.0.40 through 9.0.116. The vulnerability has a CVSS v3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N), indicating high severity primarily due to confidentiality impact.
An unauthenticated attacker with network access can exploit this vulnerability with low complexity and no user interaction required. Successful exploitation allows disclosure of sensitive information, as the improper encoding or escaping in the JsonAccessLogValve enables attackers to extract confidential data from the system.
Apache advisories recommend upgrading to mitigated versions: 11.0.21, 10.1.54, or 9.0.117, which address the issue. Further details are available in the Apache Tomcat announcement on their mailing list (https://lists.apache.org/thread/j1w7304yonlr8vo1tkb5nfs7od1y228b) and the oss-security mailing list (http://www.openwall.com/lists/oss-security/2026/04/09/26).
Details
- CWE(s)