CVE-2026-56669: Elysia Elysia Has Inefficient Algorithmic Complexity Vulnerability

HIGH
Advisory Identifier: GHSA-9643-4qgh-g8mx
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CVSS 7.5
CWE-436 CWE-407
Published
Advisory Summary

CVE-2026-56669 is a HIGH (CVSS 7.5) elysia has inefficient algorithmic complexity vulnerability (CWE-436: Interpretation Conflict) affecting Elysia libraries in the npm ecosystem. The issue involves elysia has inefficient algorithmic complexity and interpretation conflict. Remediation is available by upgrading affected packages to version 1.4.29.

CVE-2026-56669 at a Glance

CVE Identifier CVE-2026-56669
GHSA Identifier GHSA-9643-4qgh-g8mx
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-436: Interpretation Conflict
Affected Product Elysia
Package Ecosystem npm
Published Date
Last Updated

Security Impact

CVSS: 7.5

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:N/I:N/A:H).

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 High (A:H)

How to Fix CVE-2026-56669

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

elysia fixed: 1.4.29 
npm install elysia@1.4.29
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 elysia

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-56669, inspect your project dependencies using npm:

npm ls elysia

Analyze the terminal output to locate any version of Elysia in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 1.4.29), your application is affected.

Note: The npm ls elysia 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-436: Interpretation Conflict, where product a handles inputs or steps differently than product b, which causes a to perform incorrect actions based on its perception of b's state. In Elysia, 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

Elysia v1.4.28 is vulnerable to denial-of-service attacks due to CPU exhaustion in the form data normalization code. Elysia uses `getAll` to retrieve value from FormData. It is called directly relative to the total number of key-value pairs in the form data. The total amount of work the for loop has to do grows quadratically, so doubling the number of unique key-value pairs quadruples the amount of work. In the above PoC, each .getAll call scans through all of the `n` key-value pairs in the form data. Because there are `n` unique keys in the form data, there are .getAll calls, so in total the form data normalizer has to scan `n` x `n` key-value pairs. ### Impact Endpoints using `multipart/form-data` ### Patches 1.4.29 ### Workarounds no 100% confirm workaround beside updating the patch

CVE-2026-56669 Affected Elysia Versions

1 component(s)
Fixed Versions:
1.4.29
Product / Package Ecosystem Affected Versions Fixed Version
elysia
npm/elysia
npm
< 1.4.29
1.4.29

References

GitHub Advisory / Wiki ADVISORY
https://github.com/elysiajs/elysia/security/advisories/GHSA-9643-4qgh-g8mx
NVD — CVE-2026-56669 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-56669
Security Fix Commit FIX COMMIT
https://github.com/elysiajs/elysia/commit/8358ff9efbcedf9534995f5977f26b9ceab59329
Elysia Source Repository REPOSITORY
https://gist.github.com/jviide/ea040eabe7bac058326174e2cd42dfd9
Elysia Source Repository REPOSITORY
https://github.com/elysiajs/elysia
Elysia Release RELEASE
https://github.com/elysiajs/elysia/releases/tag/1.4.29

Frequently Asked Questions

What is CVE-2026-56669?
CVE-2026-56669 is a security vulnerability in Elysia involving elysia has Inefficient Algorithmic Complexity and Interpretation Conflict under CWE-436: Interpretation Conflict.
Which Elysia versions are affected?
Affected versions include releases prior to 1.4.29 across affected packages: elysia.
What version fixes CVE-2026-56669?
Upgrading to 1.4.29 (or the latest patched release for your respective branch) resolves the vulnerability.
Is elysia affected?
Yes, elysia is affected in releases prior to 1.4.29. Upgrade your dependency to 1.4.29 or later.
What is the CVSS score of CVE-2026-56669?
CVE-2026-56669 has a CVSS v3.1 base score of 7.5 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
What CWE is associated with CVE-2026-56669?
CVE-2026-56669 is classified under CWE-436: Interpretation Conflict (Product A handles inputs or steps differently than Product B, which causes A to perform incorrect actions based on its perception of B's state.).
How can I check npm dependencies for CVE-2026-56669?
Run the dependency tree command: 'npm ls elysia'. 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-9643-4qgh-g8mx",
  "modified" : "2026-09-23T21:54:50Z",
  "published" : "2026-09-23T21:54:50Z",
  "aliases" : [ "CVE-2026-56669" ],
  "summary" : "elysia has Inefficient Algorithmic Complexity and Interpretation Conflict",
  "details" : "Elysia v1.4.28 is vulnerable to denial-of-service attacks due to CPU exhaustion in the form data normalization code.\n\nElysia uses `getAll` to retrieve value from FormData. It is called directly relative to the total number of key-value pairs in the form data. The total amount of work the for loop has to do grows quadratically, so doubling the number of unique key-value pairs quadruples the amount of work. In the above PoC, each .getAll call scans through all of the `n` key-value pairs in the form data. Because there are `n` unique keys in the form data, there are .getAll calls, so in total the form data normalizer has to scan `n` x `n` key-value pairs.\n\n### Impact\nEndpoints using `multipart/form-data`\n\n### Patches\n1.4.29\n\n### Workarounds\nno 100% confirm workaround beside updating the patch",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "elysia"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.4.29"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/elysiajs/elysia/security/advisories/GHSA-9643-4qgh-g8mx"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-56669"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/elysiajs/elysia/commit/8358ff9efbcedf9534995f5977f26b9ceab59329"
  }, {
    "type" : "WEB",
    "url" : "https://gist.github.com/jviide/ea040eabe7bac058326174e2cd42dfd9"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/elysiajs/elysia"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/elysiajs/elysia/releases/tag/1.4.29"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-407", "CWE-436" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-23T21:54:50Z",
    "nvd_published_at" : "2026-07-08T21:16:50Z"
  }
}