CVE-2025-71381 Hono CVE debrief

Who should care

Defenders responsible for Hono deployments, particularly those using shared caches or proxies, should assess exposure and prioritize verification and remediation. This includes reviewing the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance. Operators, platform administrators, vulnerability management teams, and security teams should also be aware of the potential impacts and take necessary actions to verify

Why it matters

CVE-2025-71381 is a medium-severity vulnerability in Hono's CORS middleware that may lead to cache key pollution and inconsistent CORS enforcement. Defenders should prioritize verifying Hono deployments and upgrading vulnerable versions.

• Cache key pollution and inconsistent CORS enforcement may occur in environments with shared caches or proxies.
• Defenders must verify Hono deployments for vulnerability and prioritize remediation.
• Remediation requires upgrading to Hono version 4.10.3.

Technical summary

The Hono CORS middleware flaw allows an attacker to supply arbitrary Vary header values, potentially causing cache key pollution and inconsistent CORS enforcement in environments that rely on shared caches or proxies. This vulnerability affects Hono versions before 4.10.2 and is fixed in 4.10.3. Defenders should prioritize verifying Hono deployments and upgrading vulnerable versions to prevent potential cache key pollution and inconsistent CORS enforcement. The flaw is a result of the middleware copying the Vary header from the incoming request into the response, which can lead to inconsistent CORS enforcement.

Defensive priority

Defenders should prioritize verifying Hono deployments for version 4.10.2 or earlier and upgrading to 4.10.3 if vulnerable.

Recommended defensive actions

• Verify Hono deployments for version 4.10.2 or earlier
• Upgrade vulnerable Hono deployments to 4.10.3
• Monitor for potential cache key pollution and inconsistent CORS enforcement
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE record and NVD entry provide details on the vulnerability, but its actual impact and exploitation require further verification. Defenders should review the official CVE Program record and NIST NVD detail page for source-provided CVE metadata and vulnerability assessment. The Hono security advisory and Vulncheck advisory also provide source references for further information.

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.