CyberSecBulletin
CVE-2026-59083NVD status: Analyzed

Apache Tomcat: Improper Handling of URL Encoding (Hex Encoding)

Published Updated By the CyberSecBulletin desk

CVE-2026-59083 is a critical-severity improper handling of URL encoding (hex encoding) vulnerability in Apache Tomcat from Apache, with a CVSS 3.1 base score of 9.1 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. Affected Apache Tomcat versions: 11.0.0-M1 through 11.0.23; 10.1.0-M1 through 10.1.56; 9.0.0.M1 through 9.0.119, and others listed below. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.52% chance of exploitation within 30 days, which is low compared with other CVEs.

Patch this week

Critical severity: a successful attack would have severe impact.

What to do

  1. Check which version of Apache Tomcat you run against the affected versions below, and install the vendor's latest release.
  2. Read the advisory on lists.apache.org for workarounds and exact fixed builds.
  3. Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.

Affected products and versions

VendorProductAffected versionsFixed in
ApacheApache Tomcat11.0.0-M1 through 11.0.23; 10.1.0-M1 through 10.1.56; 9.0.0.M1 through 9.0.119; 8.5.0 through 8.5.100Not stated
ApacheTomcat8.0.0 and earlier; 8.5.0 through 8.5.100; 9.0.0 through 9.0.119; 10.1.0 through 10.1.56; 11.0.0 through 11.0.23Not stated

Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
NetworkCan be exploited remotely over a network, including the internet.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
NoneNo account or login is needed.
User interaction
NoneNo action by a victim is required.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
HighAll data handled by the component can be read.
Integrity
HighData or code can be modified at will.
Availability
NoneAvailability is not affected.

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N. Scored by CISA (ADP).

Official description

Improper Handling of URL Encoding (Hex Encoding) vulnerability in Apache Tomcat's rewrite valve allowed security constraint bypass for some configurations. This issue affects Apache Tomcat: from 11.0.0-M1 through 11.0.23, from 10.1.0-M1 through 10.1.56, from 9.0.0.M1 through 9.0.119, from 8.5.0 through 8.5.100. Other versions that have reached end of support may also be affected. Users are recommended to upgrade to version 11.0.24, 10.1.57 or 9.0.120, which fix the issue.

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Improper Handling of URL Encoding (Hex Encoding)

The product does not properly handle when all or part of an input has been URL encoded.

How developers prevent this class of flaw

  • Avoid making decisions based on names of resources (e.g. files) if those resources can have alternate names.
  • Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.

More Improper Handling of URL Encoding (Hex Encoding) vulnerabilities (CWE-177)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: total).

References

Third-party and government advisories

Other vulnerabilities in Apache Tomcat

All Apache Tomcat vulnerabilities

Recent Improper Handling of URL Encoding (Hex Encoding) vulnerabilities

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