CVE-2026-23903

Workarounds

• Ensure that the filesystem hosting the application is case-sensitive (e.g., Linux/Unix).
• Manually configure all Shiro filter chains to handle all possible case variations of protected filenames (not recommended due to complexity).

Resources

• CVE-2026-23903
• Mailing List Announcement
• OSS-Security List

Authentication Bypass:
A vulnerability exists in Apache Shiro that allows authentication bypass for static files when served from a case-insensitive filesystem (such as the default configuration on macOS or Windows).

The issue arises when Shiro's URL filters are configured with lower-case rules (a common default), but the underlying operating system treats mixed-case filenames as identical. An attacker can access protected static resources by varying the capitalization of the filename in the request (e.g., requesting /SECRET.TXT to bypass a rule for /secret.txt).

This issue specifically affects static file handling and does not impact dynamic resource paths that are case-sensitive.

CVE-2026-23903 has a CVSS score of 5.3 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.1.0); upgrading removes the vulnerable code path.

Kodem intelligence

Users should upgrade to Apache Shiro 2.1.0 or later.

Important Configuration Note:
Version 2.1.0 introduces a new configuration parameter to handle case-insensitivity, which must be enabled manually to resolve the issue:

• shiro.ini:

  filterChainResolver.caseInsensitive = true
  

• Spring Boot (application.properties):

  shiro.caseInsensitive=true
  

Note: Apache Shiro 3.0.0 (upcoming) will enable this setting by default.

1. What is CVE-2026-23903? CVE-2026-23903 is a medium-severity security vulnerability in org.apache.shiro:shiro-spring (maven), affecting versions <= 2.0.6. It is fixed in 2.1.0.
2. How severe is CVE-2026-23903? CVE-2026-23903 has a CVSS score of 5.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of org.apache.shiro:shiro-spring are affected by CVE-2026-23903? org.apache.shiro:shiro-spring (maven) versions <= 2.0.6 is affected.
4. Is there a fix for CVE-2026-23903? Yes. CVE-2026-23903 is fixed in 2.1.0. Upgrade to this version or later.
5. Is CVE-2026-23903 exploitable, and should I be worried? Whether CVE-2026-23903 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-23903 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-23903? Upgrade org.apache.shiro:shiro-spring to 2.1.0 or later.