CVE-2026-29085: Hono Hono Vulnerable To SSE Control Vulnerability

MODERATE
Advisory Identifier: GHSA-p6xx-57qc-3wxr
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CVSS 6.5
CWE-74
Published
Advisory Summary

CVE-2026-29085 is a MODERATE (CVSS 6.5) hono vulnerable to sse control vulnerability (CWE-74: Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')) affecting Hono libraries in the npm ecosystem. The issue involves hono vulnerable to sse control field injection via cr/lf in writesse(). Remediation is available by upgrading affected packages to version 4.12.4.

CVE-2026-29085 at a Glance

CVE Identifier CVE-2026-29085
GHSA Identifier GHSA-p6xx-57qc-3wxr
Severity MODERATE
CVSS v3.1 Base Score 6.5
CWE Classification CWE-74: Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')
Affected Product Hono
Package Ecosystem npm
Published Date
Last Updated

Security Impact

CVSS: 6.5

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:L/I:L/A:N).

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 Low (C:L)
Integrity Low (I:L)
Availability None (A:N)

How to Fix CVE-2026-29085

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: 4.12.4 
npm install hono@4.12.4
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-2026-29085, 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 4.12.4), 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-74: Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection'), where the product constructs all or part of a command, data structure, or record using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify how it is parsed or interpreted when it is sent to a downstream component. 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 When using `streamSSE()` in Streaming Helper, the `event`, `id`, and `retry` fields were not validated for carriage return (`\r`) or newline (`\n`) characters. Because the SSE protocol uses line breaks as field delimiters, this could allow injection of additional SSE fields within the same event frame if untrusted input was passed into these fields. ## Details The SSE helper builds event frames by joining lines with `\n`. While multi-line `data:` fields are handled according to the SSE specification, the `event`, `id`, and `retry` fields previously allowed raw values without rejecting embedded CR/LF characters. Including CR/LF in these control fields could allow unintended additional fields (such as `data:`, `id:`, or `retry:`) to be injected into the event stream. The issue has been fixed by rejecting CR/LF characters in these fields. ## Impact An attacker could manipulate the structure of SSE event frames if an application passed user-controlled input directly into `event`, `id`, or `retry`. Depending on application behavior, this could result in injected SSE fields or altered event stream handling. Applications that render `e.data` in an unsafe manner (for example, using `innerHTML`) could potentially expose themselves to client-side script injection. This issue affects applications that rely on the SSE helper to enforce protocol-level constraints.

CVE-2026-29085 Affected Hono Versions

1 component(s)
Fixed Versions:
4.12.4
Product / Package Ecosystem Affected Versions Fixed Version
hono
npm/hono
npm
< 4.12.4
4.12.4

References

GitHub Advisory / Wiki ADVISORY
https://github.com/honojs/hono/security/advisories/GHSA-p6xx-57qc-3wxr
NVD — CVE-2026-29085 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-29085
Security Fix Commit FIX COMMIT
https://github.com/honojs/hono/commit/f4123ed9ea3c7c52380cc99a079a4d773838846e
Hono Source Repository REPOSITORY
https://github.com/honojs/hono

Frequently Asked Questions

What is CVE-2026-29085?
CVE-2026-29085 is a security vulnerability in Hono involving Hono Vulnerable to SSE Control Field Injection via CR/LF in writeSSE() under CWE-74: Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection').
Which Hono versions are affected?
Affected versions include releases prior to 4.12.4 across affected packages: hono.
What version fixes CVE-2026-29085?
Upgrading to 4.12.4 (or the latest patched release for your respective branch) resolves the vulnerability.
Is hono affected?
Yes, hono is affected in releases prior to 4.12.4. Upgrade your dependency to 4.12.4 or later.
What is the CVSS score of CVE-2026-29085?
CVE-2026-29085 has a CVSS v3.1 base score of 6.5 (MODERATE) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N.
What CWE is associated with CVE-2026-29085?
CVE-2026-29085 is classified under CWE-74: Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection') (The product constructs all or part of a command, data structure, or record using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify how it is parsed or interpreted when it is sent to a downstream component.).
How can I check npm dependencies for CVE-2026-29085?
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-p6xx-57qc-3wxr",
  "modified" : "2026-03-05T15:26:37Z",
  "published" : "2026-03-04T19:48:41Z",
  "aliases" : [ "CVE-2026-29085" ],
  "summary" : "Hono Vulnerable to SSE Control Field Injection via CR/LF in writeSSE()",
  "details" : "## Summary\n\nWhen using `streamSSE()` in Streaming Helper, the `event`, `id`, and `retry` fields were not validated for carriage return (`\\r`) or newline (`\\n`) characters.\n\nBecause the SSE protocol uses line breaks as field delimiters, this could allow injection of additional SSE fields within the same event frame if untrusted input was passed into these fields.\n\n## Details\n\nThe SSE helper builds event frames by joining lines with `\\n`. While multi-line `data:` fields are handled according to the SSE specification, the `event`, `id`, and `retry` fields previously allowed raw values without rejecting embedded CR/LF characters.\n\nIncluding CR/LF in these control fields could allow unintended additional fields (such as `data:`, `id:`, or `retry:`) to be injected into the event stream.\n\nThe issue has been fixed by rejecting CR/LF characters in these fields.\n\n## Impact\n\nAn attacker could manipulate the structure of SSE event frames if an application passed user-controlled input directly into `event`, `id`, or `retry`.\n\nDepending on application behavior, this could result in injected SSE fields or altered event stream handling. Applications that render `e.data` in an unsafe manner (for example, using `innerHTML`) could potentially expose themselves to client-side script injection.\n\nThis issue affects applications that rely on the SSE helper to enforce protocol-level constraints.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "hono"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "4.12.4"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/honojs/hono/security/advisories/GHSA-p6xx-57qc-3wxr"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-29085"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/honojs/hono/commit/f4123ed9ea3c7c52380cc99a079a4d773838846e"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/honojs/hono"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-74" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-03-04T19:48:41Z",
    "nvd_published_at" : "2026-03-04T23:16:10Z"
  }
}