Summary
Hono: Algorithmic Complexity DoS in Language Middleware
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.
Details
To implement progressive language-tag truncation, normalizeLanguage() repeatedly calls parts.slice(0, i).join('-') for every possible prefix. 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. The default detector order enables query-string, cookie, and header detection, so applications using languageDetector() may expose this processing to unauthenticated requests.
Request-size limits reduce the maximum cost of a single request but do not eliminate the issue. Inputs accepted by common JavaScript runtimes can still cause noticeable synchronous event-loop blocking.
Resolution
The progressive lookup should avoid reconstructing every shorter prefix. The implementation can instead inspect the configured supported languages and select the longest value that matches the input at a hyphen boundary.
Impact
An attacker may repeatedly send requests containing long, hyphen-separated language tags, causing excessive CPU consumption and preventing unrelated requests from being processed.
The practical impact depends on the runtime's request-size limits, reverse-proxy configuration, and the detectors enabled by the application.
CVE-2026-71848 has a CVSS score of 5.3 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.12.34); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Already deployed Kodem?
See it in your environmentNew to Kodem? Get a demo →Remediation advice
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2026-71848? CVE-2026-71848 is a medium-severity security vulnerability in hono (npm), affecting versions >= 4.12.0, < 4.12.34. It is fixed in 4.12.34.
- How severe is CVE-2026-71848? CVE-2026-71848 has a CVSS score of 5.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of hono are affected by CVE-2026-71848? hono (npm) versions >= 4.12.0, < 4.12.34 is affected.
- Is there a fix for CVE-2026-71848? Yes. CVE-2026-71848 is fixed in 4.12.34. Upgrade to this version or later.
- Is CVE-2026-71848 exploitable, and should I be worried? Whether CVE-2026-71848 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-71848 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-71848? Upgrade
honoto 4.12.34 or later.