diff --git a/CHANGELOG.md b/CHANGELOG.md
index c544929..ba6cdb3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,7 @@
 * feature: Shorten the graph 'Add to QuickTree' action icon's title to "Add to Quicktree" so it reads cleanly as a label in the Cacti graph drilldown action menu
 * bug: Pass a boolean (not the integer 1) to api_plugin_register_hook()'s $enable argument so the hook registration stays type-correct under Cacti 1.3's strict bool type-hint (the int only coerces while the file lacks declare(strict_types=1))
 * security: Move the graph 'Add to QuickTree' icon's inline `onClick='addQuickTree()'` handler into a delegated jQuery binding in `js/quicktree.js` (via a `quicktreeAddLink` class and `data-` attributes) and replace the confirmation pages' inline `onClick='cactiReturnTo()'` Cancel buttons with the CSP-safe `cactiReturnTo` class, so the pages no longer trip Cacti's Content-Security-Policy script-src-attr directive
+* security: Require a POST request with a valid CSRF token for the add, clear and save actions using Cacti's shared guard with a fallback for older hosts, and send the add request from the graph button as a POST
 * dev: Replace the translation-template CI check that regenerated locales/po/cacti.pot and compared it with a diff-based gate (tests/bin/check-i18n-pot.php) requiring cacti.pot to be updated only when a pull request adds, removes, or modifies an i18n function call
 * dev: Measure CI coverage with xdebug instead of pcov so the plugin's own sources are instrumented (pcov auto-scopes to the Composer root and skipped cacti/plugins/, leaving the patch-coverage gate with nothing to measure)
 * security: Normalize the requested location before building the breadcrumb URL so a crafted location value is not reflected into the navigation
diff --git a/js/quicktree.js b/js/quicktree.js
index 70dafd0..083340e 100644
--- a/js/quicktree.js
+++ b/js/quicktree.js
@@ -23,13 +23,11 @@
 */
 
 function addQuickTree(local_graph_id, rra_id) {
-	var strURL = urlPath +
-		'plugins/quicktree/quicktree.php' +
-		'?action=add' +
-		'&rra_id='    + rra_id +
-		'&graph_id='  + local_graph_id;
+	const strURL = urlPath + 'plugins/quicktree/quicktree.php';
 
-	$.getJSON(strURL, function(message) {
+	$.ajax({type: 'POST', url: strURL, dataType: 'json',
+		data: {action: 'add', rra_id: rra_id, graph_id: local_graph_id},
+		success: function(message) {
 		if (message.title) {
 			sessionMessageTitle = message.title;
 		}
@@ -39,7 +37,7 @@ function addQuickTree(local_graph_id, rra_id) {
 		}
 
 		displayMessages();
-	});
+	}});
 }
 
 $(function() {
diff --git a/quicktree.php b/quicktree.php
index 806d0d2..242b25d 100644
--- a/quicktree.php
+++ b/quicktree.php
@@ -59,6 +59,23 @@
 	$action = $code_actions[$drp_action];
 }
 
+// remove stays GET until its row links become POST forms.
+if (in_array($action, ['add', 'clear', 'save'], true)) {
+	if (function_exists('csrf_require_post')) {
+		csrf_require_post();
+	} elseif (($_SERVER['REQUEST_METHOD'] ?? 'GET') !== 'POST') {
+		header('Allow: POST');
+		http_response_code(405);
+		exit;
+	}
+
+	// The 1.2.x helper checks the method only; validate the token on every host.
+	if (!function_exists('csrf_check') || !csrf_check(false)) {
+		http_response_code(403);
+		exit;
+	}
+}
+
 switch ($action) {
 	case 'add':
 		$graph = 0;
diff --git a/tests/Unit/MutationStatusTest.php b/tests/Unit/MutationStatusTest.php
new file mode 100644
index 0000000..68046bf
--- /dev/null
+++ b/tests/Unit/MutationStatusTest.php
@@ -0,0 +1,20 @@
+<?php
+/*
+ +-------------------------------------------------------------------------+
+ | Copyright (C) 2004-2026 The Cacti Group                                 |
+ +-------------------------------------------------------------------------+
+ | Cacti: The Complete RRDtool-based Graphing Solution                     |
+ +-------------------------------------------------------------------------+
+*/
+
+it('protects mutation routes with legacy, method-only and token-checking Cacti guards', function () {
+	$process = proc_open([PHP_BINARY, __DIR__ . '/../csrf-actions.php'], [1 => ['pipe', 'w'], 2 => ['pipe', 'w']], $pipes);
+	$stdout  = stream_get_contents($pipes[1]);
+	$stderr  = stream_get_contents($pipes[2]);
+	fclose($pipes[1]);
+	fclose($pipes[2]);
+
+	expect(proc_close($process))->toBe(0)
+		->and($stderr)->toBe('')
+		->and(trim($stdout))->toBe('69 mutation guard cases passed');
+});
diff --git a/tests/client-post.test.mjs b/tests/client-post.test.mjs
new file mode 100644
index 0000000..63888d9
--- /dev/null
+++ b/tests/client-post.test.mjs
@@ -0,0 +1,25 @@
+/* Copyright (C) 2026 The Cacti Group. GPL version 2 or later. */
+import assert from 'node:assert/strict';
+import { readFileSync } from 'node:fs';
+import { runInNewContext } from 'node:vm';
+import test from 'node:test';
+
+test('adding a graph sends a POST body and preserves the success notification', () => {
+	let request;
+	let notifications = 0;
+	const context = {
+		urlPath: '/cacti/',
+		$: Object.assign(() => ({}), { ajax: (options) => { request = options; } }),
+		displayMessages: () => { notifications++; },
+	};
+	runInNewContext(readFileSync(new URL('../js/quicktree.js', import.meta.url), 'utf8'), context);
+	context.addQuickTree(42, 7);
+	assert.equal(request.type, 'POST');
+	assert.equal(request.url, '/cacti/plugins/quicktree/quicktree.php');
+	assert.equal(request.dataType, 'json');
+	assert.deepEqual(JSON.parse(JSON.stringify(request.data)), {action: 'add', rra_id: 7, graph_id: 42});
+	request.success({title: 'Added', message: 'Queued'});
+	assert.equal(context.sessionMessageTitle, 'Added');
+	assert.equal(context.sessionMessage.message, 'Queued');
+	assert.equal(notifications, 1);
+});
diff --git a/tests/csrf-actions.php b/tests/csrf-actions.php
new file mode 100644
index 0000000..5e0dbbb
--- /dev/null
+++ b/tests/csrf-actions.php
@@ -0,0 +1,97 @@
+<?php
+/*
+ +-------------------------------------------------------------------------+
+ | Copyright (C) 2004-2023 Howard Jones                                    |
+ | Copyright (C) 2022 The Cacti Group                                      |
+ |                                                                         |
+ | This program is free software; you can redistribute it and/or           |
+ | modify it under the terms of the GNU General Public License             |
+ | as published by the Free Software Foundation; either version 2          |
+ | of the License, or (at your option) any later version.                  |
+ |                                                                         |
+ | This program is distributed in the hope that it will be useful,         |
+ | but WITHOUT ANY WARRANTY; without even the implied warranty of          |
+ | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the           |
+ | GNU General Public License for more details.                            |
+ +-------------------------------------------------------------------------+
+ | Cacti: The Complete RRDtool-based Graphing Solution                     |
+ +-------------------------------------------------------------------------+
+ | This code is designed, written, and maintained by the Cacti Group. See  |
+ | about.php and/or the AUTHORS file for specific developer information.   |
+ +-------------------------------------------------------------------------+
+ | http://www.cacti.net/                                                   |
+ +-------------------------------------------------------------------------+
+*/
+
+$source         = file_get_contents(__DIR__ . '/../quicktree.php');
+$start          = strpos($source, 'if ($drp_action != null)');
+$end            = strpos($source, 'switch ($action) {', $start);
+$dispatch_guard = substr($source, $start, $end - $start);
+$mutation_cases = [['GET', null, 405], ['POST', null, 403], ['POST', 'invalid', 403], ['POST', 'valid', 200]];
+$remove_cases   = [['GET', null, 200], ['POST', null, 200], ['POST', 'invalid', 200]];
+$routes         = [
+	['add', null, $mutation_cases],
+	['clear', null, $mutation_cases],
+	['save', null, $mutation_cases],
+	['', 3, $mutation_cases],
+	['view', 3, $mutation_cases],
+	['remove', null, $remove_cases],
+];
+$count = 0;
+
+foreach (['legacy', 'method-only', 'method-and-token'] as $host) {
+	foreach ($routes as $route) {
+		foreach ($route[2] as $case) {
+			[$method, $token, $expected] = $case;
+			$seed                        = var_export(['method' => $method, 'token' => $token, 'action' => $route[0], 'drp_action' => $route[1]], true);
+			$script                      = '<?php $seed = ' . $seed . ';' . <<<'PHP'
+
+$_SERVER['REQUEST_METHOD'] = $seed['method'];
+http_response_code(200);
+$action = $seed['action'];
+$drp_action = $seed['drp_action'];
+$code_actions = array(1 => 'add_tree', 2 => 'add_branch', 3 => 'clear');
+$mutated = false;
+$core_guard_calls = 0;
+function csrf_check($fatal) { return $GLOBALS['seed']['token'] === 'valid'; }
+register_shutdown_function(function () { echo json_encode(array('status' => http_response_code(), 'mutated' => $GLOBALS['mutated'], 'core_guard_calls' => $GLOBALS['core_guard_calls'])); });
+PHP;
+			$script .= "\nrequire " . var_export(__DIR__ . '/../includes/security.php', true) . ';';
+
+			if ($host !== 'legacy') {
+				$script .= <<<'PHP'
+
+function csrf_require_post() {
+	$GLOBALS['core_guard_calls']++;
+	if ($_SERVER['REQUEST_METHOD'] !== 'POST') {
+		header('Allow: POST');
+		http_response_code(405);
+		exit;
+	}
+PHP;
+
+				if ($host === 'method-and-token') {
+					$script .= 'if (!csrf_check(false)) { http_response_code(403); exit; }';
+				}
+				$script .= "\n}\n";
+			}
+			$script .= "\n" . $dispatch_guard . "\n\$mutated = true;";
+			$process = proc_open([PHP_BINARY], [0 => ['pipe', 'r'], 1 => ['pipe', 'w'], 2 => ['pipe', 'w']], $pipes);
+			fwrite($pipes[0], $script);
+			fclose($pipes[0]);
+			$result = json_decode(stream_get_contents($pipes[1]), true);
+			$stderr = stream_get_contents($pipes[2]);
+			fclose($pipes[1]);
+			fclose($pipes[2]);
+
+			$uses_core_guard = $host !== 'legacy' && (in_array($route[0], ['add', 'clear', 'save'], true) || $route[1] === 3);
+
+			if (proc_close($process) !== 0 || $stderr !== '' || $result['status'] !== $expected || $result['mutated'] !== ($expected === 200) || $result['core_guard_calls'] !== (int) $uses_core_guard) {
+				throw new RuntimeException('QuickTree mutation guard regression: ' . $stderr);
+			}
+
+			$count++;
+		}
+	}
+}
+print "$count mutation guard cases passed\n";