CVE-2026-71848 honojs CVE debrief

Who should care

Defenders responsible for Hono applications using the languageDetector middleware should assess exposure and prioritize upgrading to version 4.12.34. This includes reviewing the current configuration of language detection and verifying if any applications are using vulnerable versions of the middleware. Additionally, defenders should monitor for potential denial-of-service attacks and review compensating controls for exposed systems.

Why it matters

CVE-2026-71848 is a denial-of-service vulnerability in Hono's languageDetector middleware. Defenders should prioritize verifying exposure and upgrading to version 4.12.34 if vulnerable.

• Excessive CPU consumption may prevent unrelated requests from being processed
• Verify exposure and upgrade to version 4.12.34 if vulnerable
• Monitor for potential denial-of-service attacks

Technical summary

The languageDetector middleware in Hono is vulnerable to algorithmic complexity denial of service when processing crafted language tags. This issue arises from the middleware's progressive language tag truncation implementation, which repeatedly processes subtags, leading to excessive CPU consumption. The vulnerability is fixed in version 4.12.34. Defenders should prioritize verifying exposure and upgrading to the fixed version if vulnerable. The vulnerability may be triggered through various sources, including query parameters, cookies, Accept-Language headers, or URL paths, depending on the detector configuration.

Defensive priority

Defenders should prioritize verifying exposure and upgrading to version 4.12.34 if vulnerable.

Recommended defensive actions

• Verify if applications using Hono's languageDetector middleware are exposed to this vulnerability
• Upgrade to version 4.12.34 if vulnerable
• Monitor for potential excessive CPU consumption
• 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 and its fix. Additional information on potential exploitation and impact is limited. Defenders should verify if applications using Hono's languageDetector middleware are exposed and monitor for potential denial-of-service attacks. The lack of detailed information on exploitation attempts or successful attacks limits the ability to assess real-world impact.

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.