CVE-2026-71848 honojs CVE debrief

Who should care

Defenders responsible for Hono applications should assess exposure and prioritize upgrading to version 4.12.34 or later. They should also monitor for unusual traffic patterns and implement rate limiting on language tag inputs.

Why it matters

CVE-2026-71848 is a denial-of-service vulnerability affecting Hono versions 4.12.0 through 4.12.33. Defenders should prioritize upgrading to version 4.12.34 or later and monitor for unusual traffic patterns.

• Excessive CPU consumption can prevent unrelated requests from being processed, potentially leading to denial-of-service.
• Defenders should verify if their Hono applications are using vulnerable versions of the languageDetector middleware.
• Remediation priority is high for applications using vulnerable versions, as an attacker may repeatedly send requests containing long, hyphen-separated language tags.

Technical summary

The languageDetector middleware in Hono versions 4.12.0 through 4.12.33 is vulnerable to algorithmic complexity denial of service. An attacker may send requests with long, hyphen-separated language tags, causing excessive CPU consumption and preventing unrelated requests from being processed. The vulnerability is due to inefficient language tag processing, which grows quadratically with the number of subtags. Language values may come from a query parameter, cookie, Accept-Language header, or URL path, depending on the detector configuration. The default detector order enables query string, cookie, and header detection, so applications using languageDetector() may expose this processing to unauthenticated.

Defensive priority

Defenders should prioritize upgrading to version 4.12.34 or later to mitigate this vulnerability. They should also monitor for unusual traffic patterns and implement rate limiting on language tag inputs.

Recommended defensive actions

• Upgrade to Hono version 4.12.34 or later
• Monitor for unusual traffic patterns
• Implement rate limiting on language tag inputs
• 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, including its description, affected versions, and fixed version. The GitHub commit and release notes confirm the fix in version 4.12.34.

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.