CVE-2026-71848: honojs hono Inefficient Algorithmic Complexity

Vulnerability summary

CVE-2026-71848 is a medium (CVSS 5.3) Inefficient Algorithmic Complexity vulnerability in honojs hono. EPSS estimates a 0.51% chance of exploitation in the next 30 days, higher than 42% of scored vulnerabilities.

Timeline

1. 07-08-2026
   PublishedVulnerability first disclosed.
2. 08-08-2026
   Last modifiedVulnerability information updated.

Description

Hono is a Web application framework that provides support for any JavaScript runtime. From 4.12.0 to 4.12.33, the languageDetector middleware is vulnerable to algorithmic complexity denial of service when processing a crafted language tag containing a large number of hyphen separated subtags. To implement progressive language tag truncation, normalizeLanguage() repeatedly calls parts.slice(0, i).join('-') for every possible prefix, so the total amount of string processing 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, and the default detector order enables query string, cookie, and header detection, so applications using languageDetector() may expose this processing to unauthenticated requests. An attacker may repeatedly send requests containing long, hyphen separated language tags, causing excessive CPU consumption and preventing unrelated requests from being processed. This issue is fixed in version 4.12.34.

• CWE-407Inefficient Algorithmic ComplexityAn algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached.