CVE-2026-71848: Hono Denial of Service Vulnerability

MODERATE
Advisory Identifier: GHSA-54fx-42gc-7vw4
Share
CVSS 5.3
CWE-407
Published
Advisory Summary

CVE-2026-71848 is a MODERATE (CVSS 5.3) denial of service vulnerability (CWE-407: Inefficient Algorithmic Complexity) affecting Hono libraries in the npm ecosystem. The issue involves algorithmic complexity dos in language middleware. Remediation is available by upgrading affected packages to version 4.12.34.

CVE-2026-71848 at a Glance

CVE Identifier CVE-2026-71848
GHSA Identifier GHSA-54fx-42gc-7vw4
Severity MODERATE
CVSS v3.1 Base Score 5.3
CWE Classification CWE-407: Inefficient Algorithmic Complexity
Affected Product Hono
Package Ecosystem npm
Published Date
Last Updated

Security Impact

CVSS: 5.3

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity None (I:N)
Availability Low (A:L)

How to Fix CVE-2026-71848

To remediate this vulnerability, upgrade all affected Hono dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

hono fixed: 4.12.34 
npm install hono@4.12.34
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

npm ls hono

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-71848, inspect your project dependencies using npm:

npm ls hono

Analyze the terminal output to locate any version of Hono in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 4.12.34), your application is affected.

Note: The npm ls hono command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-407: Inefficient Algorithmic Complexity, where an 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. In Hono, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### Summary 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. ### 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. ### 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.

CVE-2026-71848 Affected Hono Versions

1 component(s)
Fixed Versions:
4.12.34
Product / Package Ecosystem Affected Versions Fixed Version
hono
npm/hono
npm
≥ 4.12.0
< 4.12.34
4.12.34

References

GitHub Advisory / Wiki ADVISORY
https://github.com/honojs/hono/security/advisories/GHSA-54fx-42gc-7vw4
Security Fix Commit FIX COMMIT
https://github.com/honojs/hono/commit/f70e2c31684387b3231cc38512a31df6ca76a1c7
Hono Source Repository REPOSITORY
https://github.com/honojs/hono
Hono Release RELEASE
https://github.com/honojs/hono/releases/tag/v4.12.34

Frequently Asked Questions

What is CVE-2026-71848?
CVE-2026-71848 is a security vulnerability in Hono involving Algorithmic Complexity DoS in Language Middleware under CWE-407: Inefficient Algorithmic Complexity.
Which Hono versions are affected?
Affected versions include releases prior to 4.12.34 across affected packages: hono.
What version fixes CVE-2026-71848?
Upgrading to 4.12.34 (or the latest patched release for your respective branch) resolves the vulnerability.
Is hono affected?
Yes, hono is affected in releases prior to 4.12.34. Upgrade your dependency to 4.12.34 or later.
What is the CVSS score of CVE-2026-71848?
CVE-2026-71848 has a CVSS v3.1 base score of 5.3 (MODERATE) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L.
What CWE is associated with CVE-2026-71848?
CVE-2026-71848 is classified under CWE-407: Inefficient Algorithmic Complexity (An 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.).
How can I check npm dependencies for CVE-2026-71848?
Run the dependency tree command: 'npm ls hono'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-54fx-42gc-7vw4",
  "modified" : "2026-08-07T18:36:31Z",
  "published" : "2026-08-07T18:36:31Z",
  "aliases" : [ "CVE-2026-71848" ],
  "summary" : "Hono: Algorithmic Complexity DoS in Language Middleware",
  "details" : "### Summary\n\nThe `languageDetector` middleware is vulnerable to algorithmic complexity denial of service when processing a crafted language tag containing a large number of hyphen-separated subtags.\n\n### Details\n\nTo 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.\n\nLanguage 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.\n\nRequest-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.\n\n### Impact\n\nAn attacker may repeatedly send requests containing long, hyphen-separated language tags, causing excessive CPU consumption and preventing unrelated requests from being processed.\n\nThe practical impact depends on the runtime's request-size limits, reverse-proxy configuration, and the detectors enabled by the application.\n\n### Resolution\n\nThe 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.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "hono"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.12.0"
      }, {
        "fixed" : "4.12.34"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/honojs/hono/security/advisories/GHSA-54fx-42gc-7vw4"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/honojs/hono/commit/f70e2c31684387b3231cc38512a31df6ca76a1c7"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/honojs/hono"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/honojs/hono/releases/tag/v4.12.34"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-407" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-08-07T18:36:31Z",
    "nvd_published_at" : null
  }
}