CVE-2026-71849: Hono Proxy Helper Does Not Remove Vulnerability

LOW
Advisory Identifier: GHSA-79qm-7rj5-m7r9
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CVSS 3.7
CWE-200
Published
Advisory Summary

CVE-2026-71849 is a LOW (CVSS 3.7) proxy helper does not remove vulnerability (CWE-200: Exposure of Sensitive Information to an Unauthorized Actor) affecting Hono libraries in the npm ecosystem. The issue involves proxy helper does not remove response headers listed in the `connection` header. Remediation is available by upgrading affected packages to version 4.12.34.

CVE-2026-71849 at a Glance

CVE Identifier CVE-2026-71849
GHSA Identifier GHSA-79qm-7rj5-m7r9
Severity LOW
CVSS v3.1 Base Score 3.7
CWE Classification CWE-200: Exposure of Sensitive Information to an Unauthorized Actor
Affected Product Hono
Package Ecosystem npm
Published Date
Last Updated

Security Impact

CVSS: 3.7

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

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

How to Fix CVE-2026-71849

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-2026-71849, 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-200: Exposure of Sensitive Information to an Unauthorized Actor, where the product exposes sensitive information to an actor that is not explicitly authorized to have access to that information. 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 Proxy Helper (`hono/proxy`) does not remove response headers named by the origin's `Connection` header. Headers that the origin marked as connection-scoped are therefore forwarded to clients. ### Details Per RFC 9110 Section 7.6.1, an intermediary must remove the header fields listed in a message's `Connection` header field before forwarding the message, in addition to the well-known hop-by-hop headers. The `proxy()` function removed the well-known hop-by-hop headers (including `Connection` itself) from origin responses, but did not remove the headers that the response's `Connection` header field designated as connection-scoped. This issue arises when an application proxies responses from an origin that declares additional, non-standard headers as hop-by-hop via the `Connection` response header. ### Impact A client may receive response headers that the origin intended only for its immediate peer. This may lead to: - Disclosure of connection-scoped or internal metadata contained in such headers This issue affects applications that use the Proxy Helper (`hono/proxy`) to forward responses from origins that list custom header names in their `Connection` response header. Applications whose origins only use the standard hop-by-hop headers are not affected.

CVE-2026-71849 Affected Hono Versions

1 component(s)
Fixed Versions:
4.12.34
Product / Package Ecosystem Affected Versions Fixed Version
hono
npm/hono
npm
≥ 4.7.0
< 4.12.34
4.12.34

References

Hono Source Repository REPOSITORY
https://github.com/honojs/hono
GitHub Advisory / Wiki ADVISORY
https://github.com/honojs/hono/security/advisories/GHSA-79qm-7rj5-m7r9
Security Fix Commit FIX COMMIT
https://github.com/honojs/hono/commit/720b566290793d4358bf39843adcb7cf4da4548f
Hono Release RELEASE
https://github.com/honojs/hono/releases/tag/v4.12.34

Frequently Asked Questions

What is CVE-2026-71849?
CVE-2026-71849 is a security vulnerability in Hono involving Proxy Helper does not remove response headers listed in the `Connection` header under CWE-200: Exposure of Sensitive Information to an Unauthorized Actor.
Which Hono versions are affected?
Affected versions include releases prior to 4.12.34 across affected packages: hono.
What version fixes CVE-2026-71849?
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-2026-71849?
CVE-2026-71849 has a CVSS v3.1 base score of 3.7 (LOW) with vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N.
What CWE is associated with CVE-2026-71849?
CVE-2026-71849 is classified under CWE-200: Exposure of Sensitive Information to an Unauthorized Actor (The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information.).
How can I check npm dependencies for CVE-2026-71849?
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-79qm-7rj5-m7r9",
  "modified" : "2026-08-07T18:38:48Z",
  "published" : "2026-08-07T18:38:48Z",
  "aliases" : [ "CVE-2026-71849" ],
  "summary" : "Hono: Proxy Helper does not remove response headers listed in the `Connection` header",
  "details" : "### Summary\n\nThe Proxy Helper (`hono/proxy`) does not remove response headers named by the origin's `Connection` header. Headers that the origin marked as connection-scoped are therefore forwarded to clients.\n\n### Details\n\nPer RFC 9110 Section 7.6.1, an intermediary must remove the header fields listed in a message's `Connection` header field before forwarding the message, in addition to the well-known hop-by-hop headers. The `proxy()` function removed the well-known hop-by-hop headers (including `Connection` itself) from origin responses, but did not remove the headers that the response's `Connection` header field designated as connection-scoped.\n\nThis issue arises when an application proxies responses from an origin that declares additional, non-standard headers as hop-by-hop via the `Connection` response header.\n\n### Impact\n\nA client may receive response headers that the origin intended only for its immediate peer. This may lead to:\n\n- Disclosure of connection-scoped or internal metadata contained in such headers\n\nThis issue affects applications that use the Proxy Helper (`hono/proxy`) to forward responses from origins that list custom header names in their `Connection` response header. Applications whose origins only use the standard hop-by-hop headers are not affected.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "hono"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.7.0"
      }, {
        "fixed" : "4.12.34"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/honojs/hono/security/advisories/GHSA-79qm-7rj5-m7r9"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/honojs/hono/commit/720b566290793d4358bf39843adcb7cf4da4548f"
  }, {
    "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-200" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-08-07T18:38:48Z",
    "nvd_published_at" : null
  }
}