CVE-2026-56091 Apache Software Foundation CVE debrief

Who should care

Defenders responsible for Apache Shiro deployments, particularly those using the shiro-guice module in a web servlet context, should assess exposure and prioritize upgrading to a fixed version.

Why it matters

CVE-2026-56091 is a high-severity vulnerability in Apache Shiro's shiro-guice module, which can lead to authentication bypass in a web servlet context. Defenders should prioritize upgrading to Apache Shiro version 3.0.0 or later to address the vulnerability. The vulnerability affects all Apache Shiro versions through 2.x and 3.0.0-alpha-1. Further verification is needed to confirm the scope of affected systems and potential workarounds.

• Potential authentication bypass in Apache Shiro deployments
• Possible unauthorized access to sensitive data or systems
• Need for verification of affected systems and deployments
• Priority on upgrading to Apache Shiro version 3.0.0 or later

Technical summary

The vulnerability occurs when using Apache Shiro with the shiro-guice module in a web servlet context. A specially crafted HTTP request may cause an authentication bypass. This issue affects all Apache Shiro versions through 2.x, and 3.0.0-alpha-1 only when using shiro-guice module in a web servlet context. The vulnerability can be mitigated by upgrading to Apache Shiro version 3.0.0 or later. Defenders should prioritize upgrading to a fixed version and review affected systems and deployments. Further verification is needed to confirm the scope of affected systems and potential workarounds.

Defensive priority

Defenders should prioritize upgrading to Apache Shiro version 3.0.0 or later to address the authentication bypass vulnerability.

Recommended defensive actions

• Upgrade to Apache Shiro version 3.0.0 or later
• Review and update affected systems and deployments
• Monitor for potential exploitation attempts
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up
• Review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance
• Plan vendor-supported updates or mitigations through normal change control where exposure is confirmed
• Check relevant monitoring, detection, and logs for exposed assets that need extra review

Evidence notes

The CVE record and NVD entry provide details on the vulnerability, its impact, and affected versions. However, further verification is needed to confirm the scope of affected systems and potential workarounds.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.