diff --git a/.gitignore b/.gitignore
index 441e8861..fa84af9e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -22,3 +22,15 @@ test-complete-app-mlDeploy/.gradle
 
 # Compiled TypeScript test files
 test-typescript/*.js
+
+# AI generated documents
+documents
+
+# Generated proxy stubs (created by gulp setupProxyTests / generateProxyTests)
+# Files in the generated directory are fully generated
+test-basic-proxy/lib/generated/
+# the proxy stubs (non-Test.js) are generated; the *Test.js files are hand-written and must be kept
+test-basic-proxy/lib/positive/*.js
+!test-basic-proxy/lib/positive/*Test.js
+test-basic-proxy/lib/negative/*.js
+!test-basic-proxy/lib/negative/*Test.js
diff --git a/CHANGELOG.md b/CHANGELOG.md
index b9566f56..1e7b5e94 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,15 @@
 # CHANGELOG
 
+## 4.2.0
+
+#### Security Fix
+
+- Session IDs generated by `SessionState` now use `crypto.randomBytes()` instead of `Math.random()`, replacing a
+  non-cryptographic PRNG (xorshift128+) with a cryptographically secure source of randomness (CWE-338).
+  The session ID is now a 16-character hex string (8 random bytes), matching the format MarkLogic uses for its own
+  server-generated session IDs. The return type of `SessionState.sessionId()` changes from `number` to `string`.
+  Callers that only use the session ID for logging or cookie headers are unaffected.
+
 ## 4.1.0
 
 - Added TypeScript typings for core client/document/connection APIs, with better autocomplete and compile-time checks to catch mistakes earlier.
diff --git a/lib/session-state.js b/lib/session-state.js
index 29c5d0d7..e90863bd 100644
--- a/lib/session-state.js
+++ b/lib/session-state.js
@@ -1,8 +1,10 @@
 /*
-* Copyright (c) 2015-2025 Progress Software Corporation and/or its subsidiaries or affiliates. All Rights Reserved.
+* Copyright (c) 2015-2026 Progress Software Corporation and/or its subsidiaries or affiliates. All Rights Reserved.
 */
 'use strict';
 
+const crypto = require('crypto');
+
 /**
  * Identifies a server state for sharing across multiple calls to server endpoints.
  *
@@ -14,13 +16,12 @@ class SessionState {
    * Constructs an identifier for session state on the server.
    */
   constructor() {
-    // TODO: use BigInt?
-    this._sessionId = Math.floor(Math.random() * Number.MAX_SAFE_INTEGER);
+    this._sessionId = crypto.randomBytes(8).toString('hex');
   }
 
   /**
    * Provides the identifier used for the server state (for instance, for use in logging).
-   * @returns {number} the session identifier
+   * @returns {string} the session identifier
    */
   sessionId() {
     return this._sessionId;
diff --git a/test-basic/session-state-test.js b/test-basic/session-state-test.js
new file mode 100644
index 00000000..440b4fef
--- /dev/null
+++ b/test-basic/session-state-test.js
@@ -0,0 +1,38 @@
+/*
+* Copyright (c) 2015-2026 Progress Software Corporation and/or its subsidiaries or affiliates. All Rights Reserved.
+*/
+'use strict';
+
+const assert = require('assert');
+const SessionState = require('../lib/session-state.js');
+
+describe('SessionState', function () {
+  it('sessionId() returns a non-empty string', function () {
+    const session = new SessionState();
+    const id = session.sessionId();
+    assert.strictEqual(typeof id, 'string');
+    assert.ok(id.length > 0, 'sessionId should not be empty');
+  });
+
+  it('sessionId() returns a 16-character hex string (8 random bytes)', function () {
+    const session = new SessionState();
+    const id = session.sessionId();
+    assert.match(id, /^[0-9a-f]{16}$/, 'sessionId should be a 16-character lowercase hex string');
+  });
+
+  it('sessionId() returns the same value on repeated calls to the same instance', function () {
+    const session = new SessionState();
+    const id1 = session.sessionId();
+    const id2 = session.sessionId();
+    const id3 = session.sessionId();
+    assert.strictEqual(id1, id2, 'sessionId should be stable across calls');
+    assert.strictEqual(id2, id3, 'sessionId should be stable across calls');
+  });
+
+  it('two instances created in rapid succession produce different session IDs', function () {
+    const session1 = new SessionState();
+    const session2 = new SessionState();
+    assert.notStrictEqual(session1.sessionId(), session2.sessionId(),
+      'session IDs from two distinct instances should not be equal');
+  });
+});