diff --git a/.github/workflows/php-unit-tests.yml b/.github/workflows/php-unit-tests.yml
index 89eb1ad4..da6cba4a 100644
--- a/.github/workflows/php-unit-tests.yml
+++ b/.github/workflows/php-unit-tests.yml
@@ -72,8 +72,19 @@ jobs:
       # Thold contributes no parallel vendor directory or PHPUnit dependency.
       - name: Build Cacti test image
         run: |
-          docker build --tag cacti-web --file cacti-toolchain/docker/Dockerfile cacti-toolchain/docker
-          docker build --tag cacti-thold-test --file cacti-toolchain/docker/Dockerfile.test cacti-toolchain
+          for attempt in 1 2 3; do
+            if docker build --tag cacti-web --file cacti-toolchain/docker/Dockerfile cacti-toolchain/docker && \
+              docker build --tag cacti-thold-test --file cacti-toolchain/docker/Dockerfile.test cacti-toolchain; then
+              exit 0
+            fi
+
+            if [ "$attempt" -lt 3 ]; then
+              sleep 10
+            fi
+          done
+
+          echo 'Cacti test image build failed after three attempts.' >&2
+          exit 1
 
       - name: Lint every PHP source file
         run: |
diff --git a/.github/workflows/plugin-ci-workflow.yml b/.github/workflows/plugin-ci-workflow.yml
index 5e4f3db6..73630b54 100644
--- a/.github/workflows/plugin-ci-workflow.yml
+++ b/.github/workflows/plugin-ci-workflow.yml
@@ -35,21 +35,12 @@ jobs:
   integration-test:
     runs-on: ${{ matrix.os }}
     
-    # A failure against the pinned release is a real failure. The develop entry
-    # is advisory: it is how a core regression becomes visible here, but it must
-    # not turn the plugin's own pull requests red.
-    continue-on-error: ${{ matrix.cacti != 'release/1.2.31' }}
-
     strategy:
       fail-fast: false
       matrix:
         php: ['8.1', '8.2', '8.3', '8.4']
         os: [ubuntu-latest]
         cacti: ['release/1.2.31']
-        include:
-          - php: '8.4'
-            os: ubuntu-latest
-            cacti: 'develop'
     
     services:
       mariadb:
@@ -95,7 +86,24 @@ jobs:
         echo "PHP_BINARY=$(command -v php)" >> "$GITHUB_ENV"
     
     - name: Run apt-get update
-      run: sudo apt-get update
+      run: |
+        for attempt in 1 2 3; do
+          if sudo timeout 3m apt-get \
+            -o Dpkg::Lock::Timeout=60 \
+            -o Acquire::Retries=3 \
+            -o Acquire::http::Timeout=30 \
+            -o Acquire::https::Timeout=30 \
+            update; then
+            exit 0
+          fi
+
+          if [ "$attempt" -lt 3 ]; then
+            sleep 10
+          fi
+        done
+
+        echo 'apt-get update failed after three bounded attempts.' >&2
+        exit 1
     
     - name: Install System Dependencies
       run: sudo apt-get install -y apache2 snmp snmpd rrdtool fping
@@ -141,7 +149,18 @@ jobs:
       run: |
         cd ${{ github.workspace }}/cacti
         if [ -f composer.json ]; then
-          sudo composer install --prefer-dist --no-progress
+          for attempt in 1 2 3; do
+            if sudo composer install --prefer-dist --no-progress --no-interaction; then
+              exit 0
+            fi
+
+            if [ "$attempt" -lt 3 ]; then
+              sleep 10
+            fi
+          done
+
+          echo 'Composer install failed after three attempts.' >&2
+          exit 1
         fi
     
     - name: Create Cacti config.php
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9b7db7d7..08fa0ee2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,7 @@
 * issue#719: Plugin Disabled due to mix of string and int
 * issue: All Columns checkd on Thresholds page
 * issue: Special character previous value handling broken on data query indexes with special characters
+* security: Replace md5() with sha256 for email dedup cache key (GHSA-gf2h-84m3-q6m3, CWE-1240)
 
 --- 1.8.2 ---
 
diff --git a/tests/Unit/NotificationEmailDeduplicationTest.php b/tests/Unit/NotificationEmailDeduplicationTest.php
new file mode 100644
index 00000000..ba618eea
--- /dev/null
+++ b/tests/Unit/NotificationEmailDeduplicationTest.php
@@ -0,0 +1,54 @@
+<?php
+/*
+ +-------------------------------------------------------------------------+
+ | Copyright (C) 2004-2026 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.                  |
+ +-------------------------------------------------------------------------+
+ | Cacti: The Complete RRDtool-based Graphing Solution                     |
+ +-------------------------------------------------------------------------+
+ | http://www.cacti.net/                                                   |
+ +-------------------------------------------------------------------------+
+*/
+
+beforeAll(function() {
+	thold_test_load(dirname(__DIR__, 2) . '/thold_functions.php');
+});
+
+beforeEach(function() {
+	CactiStubs::reset();
+	CactiStubs::$configOptions['alert_deadnotify_one_mail'] = 'on';
+});
+
+test('combined device notifications use the sha256 deduplication path', function() {
+	$event = [
+		'from'        => ['sender@example.com'],
+		'to'          => 'operator@example.com',
+		'cc'          => '',
+		'bcc'         => '',
+		'replyto'     => '',
+		'subject'     => 'Device is down',
+		'body'        => '<body>Device is down</body>',
+		'body_text'   => 'Device is down',
+		'attachments' => [],
+		'headers'     => [],
+		'html'        => true,
+	];
+
+	CactiStubs::willReturn('db_fetch_assoc', [[
+		'id'         => 42,
+		'topic'      => 'thold_dhost_mail',
+		'event_data' => json_encode($event),
+	]]);
+
+	process_device_notifications(0, 'all', 0);
+
+	$source = file_get_contents(dirname(__DIR__, 2) . '/thold_functions.php');
+
+	expect(CactiStubs::$mail)->toHaveCount(1)
+		->and($source)->toContain("hash('sha256', json_encode(")
+		->not->toContain('md5(json_encode(');
+});
diff --git a/thold_functions.php b/thold_functions.php
index 018cf99b..23319ba1 100644
--- a/thold_functions.php
+++ b/thold_functions.php
@@ -7307,7 +7307,7 @@ function process_device_notifications($pid, $max_records, $prev_suspended) {
 							WHERE id = ?',
 							[$error_code, str_replace("\n", ' ', $error), $nend - $nstart, $r['id']]);
 					} else {
-						$id = md5(json_encode([$from, $to, $cc, $bcc, $replyto]));
+						$id = hash('sha256', json_encode([$from, $to, $cc, $bcc, $replyto]));
 
 						if (!isset($emails[$id])) {
 							$emails[$id]['from']          = $from;