What is CVE-2026-34483?

CVE-2026-34483 is a high-severity vulnerability in Apache Tomcat, classified under Improper Encoding or Escaping of Output. CVSS score: 7.5/10. Published 2026-04-09.

How severe is CVE-2026-34483?

High severity. CVSS v3 base score is 7.5 out of 10.

Vulnerability in Apache Tomcat

CVE-2026-34483

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 or 9.0.117 , which fix the issue.

Published 2026-04-09 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N.

EPSS exploit prediction

EPSS: 0.006 (47.7th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 48th percentile — 47.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.005 · newest: 0.006 · change: +0.002

Affected products

Apache Tomcat
Apache Software Foundation Tomcat — versions 11.0.0-M1, 10.1.0-M1, 9.0.40

Weakness classification (CWE)

CWE-116 — Improper Encoding or Escaping of Output

References

lists.apache.org/thread/j1w7304yonlr8vo1tkb5nfs7od1y228b (vendor-advisory, Mailing List, Vendor Advisory)
af854a3a-2127-422b-91ae-364da2661108 (Mailing List, Third Party Advisory)

Frequently asked questions

What is CVE-2026-34483?: CVE-2026-34483 is a high-severity vulnerability in Apache Tomcat, classified under Improper Encoding or Escaping of Output. CVSS score: 7.5/10. Published 2026-04-09.
How severe is CVE-2026-34483?: High severity. CVSS v3 base score is 7.5 out of 10.