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Vulnerability · Published Aug 7, 2026 · Assigned by GitHub_M

CVE-2026-71848Hono: Algorithmic Complexity DoS in Language Middleware

Medium 5.3

In plain English

A medium-severity security flaw in hono from honojs. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 43% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)5.3Medium
Exploit odds (30 days)0.5%top 56.6% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
npmhono4.12.34GHSA-54fx-42gc-7vw4

Affected products (as reported)

VendorProductVersions
honojs hono >= 4.12.0, < 4.12.34

Weakness: CWE-407 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

References