diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 90d53ef00..905a6c200 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -2,6 +2,8 @@ name: CI
 
 on: [push, pull_request, workflow_dispatch]
 
+permissions: {}
+
 jobs:
   migrations:
     if: github.event_name != 'push' || github.event.repository.fork == true || github.ref == 'refs/heads/main'
diff --git a/.github/workflows/static.yml b/.github/workflows/static.yml
index d82cae171..edb234a97 100644
--- a/.github/workflows/static.yml
+++ b/.github/workflows/static.yml
@@ -2,6 +2,8 @@ name: Check collectstatic
 
 on: [push, pull_request, workflow_dispatch]
 
+permissions: {}
+
 jobs:
   collectstatic:
     if: github.event_name != 'push' || github.event.repository.fork == true || github.ref == 'refs/heads/main'
diff --git a/apps/events/templates/events/event_detail.html b/apps/events/templates/events/event_detail.html
index 80773bd6b..35dcdd55a 100644
--- a/apps/events/templates/events/event_detail.html
+++ b/apps/events/templates/events/event_detail.html
@@ -184,7 +184,10 @@ <h3 class="widget-title">More events in <!-- The current category--><a href="{{
 <script>
 $(function(){
     $('#dataRangeSelect').change(function(e) {
-        window.location = $(this).val();
+        let url = $(this).val();
+        if (url && url.charAt(0) === '/' && url.charAt(1) !== '/') {
+            window.location = url;
+        }
     });
 });
 </script>
diff --git a/apps/mailing/forms.py b/apps/mailing/forms.py
index f16f8a64e..56031769b 100644
--- a/apps/mailing/forms.py
+++ b/apps/mailing/forms.py
@@ -1,7 +1,7 @@
 """Forms for the mailing app."""
 
 from django import forms
-from django.template import Context, Template, TemplateSyntaxError
+from django.template import Context, TemplateSyntaxError
 
 from apps.mailing.models import BaseEmailTemplate
 
@@ -13,7 +13,7 @@ def clean_content(self):
         """Validate that the content field contains valid Django template syntax."""
         content = self.cleaned_data["content"]
         try:
-            template = Template(content)
+            template = BaseEmailTemplate.template_engine.from_string(content)
             template.render(Context({}))
         except TemplateSyntaxError as e:
             raise forms.ValidationError(e) from e
diff --git a/apps/mailing/models.py b/apps/mailing/models.py
index 6f5d79bf5..dd74824d4 100644
--- a/apps/mailing/models.py
+++ b/apps/mailing/models.py
@@ -2,7 +2,7 @@
 
 from django.core.mail import EmailMessage
 from django.db import models
-from django.template import Context, Template
+from django.template import Context, Engine
 from django.urls import reverse
 
 
@@ -33,15 +33,20 @@ def preview_content_url(self):
         url_name = f"admin:{prefix}_preview"
         return reverse(url_name, args=[self.pk])
 
+    template_engine = Engine(
+        builtins=["django.template.defaultfilters"],
+        autoescape=True,
+    )
+
     def render_content(self, context):
-        """Render the email body using the Django template engine."""
-        template = Template(self.content)
+        """Render the email body using a sandboxed Django template engine."""
+        template = self.template_engine.from_string(self.content)
         ctx = Context(context)
         return template.render(ctx)
 
     def render_subject(self, context):
-        """Render the email subject using the Django template engine."""
-        template = Template(self.subject)
+        """Render the email subject using a sandboxed Django template engine."""
+        template = self.template_engine.from_string(self.subject)
         ctx = Context(context)
         return template.render(ctx)
 
diff --git a/apps/pages/management/commands/fix_success_story_images.py b/apps/pages/management/commands/fix_success_story_images.py
index c355b5dec..a0f05dd6b 100644
--- a/apps/pages/management/commands/fix_success_story_images.py
+++ b/apps/pages/management/commands/fix_success_story_images.py
@@ -1,13 +1,12 @@
 import re
-from pathlib import Path
+from pathlib import PurePosixPath
 from urllib.parse import urlparse
 
 import requests
-from django.conf import settings
-from django.core.files import File
+from django.core.files.base import ContentFile
 from django.core.management.base import BaseCommand
 
-from apps.pages.models import Image, Page, page_image_path
+from apps.pages.models import Image, Page
 
 HTTP_OK = 200
 
@@ -18,14 +17,6 @@ class Command(BaseCommand):
     def get_success_pages(self):
         return Page.objects.filter(path__startswith="about/success/")
 
-    def image_url(self, path):
-        """
-        Given a full filesystem path to an image, return the proper media
-        url for it
-        """
-        new_url = path.replace(settings.MEDIA_ROOT, settings.MEDIA_URL)
-        return new_url.replace("//", "/")
-
     def fix_image(self, path, page):
         url = f"http://legacy.python.org{path}"
         # Retrieve the image
@@ -34,27 +25,18 @@ def fix_image(self, path, page):
         if r.status_code != HTTP_OK:
             return None
 
-        # Create new associated image and generate ultimate path
+        # Extract and validate filename (alphanumeric, hyphens, dots only)
+        raw_name = PurePosixPath(urlparse(url).path).name
+        filename = re.sub(r"[^\w.\-]", "_", raw_name)
+        if not filename or filename.startswith("."):
+            return None
+
+        # Use Django's storage API to safely write the file
         img = Image()
         img.page = page
+        img.image.save(filename, ContentFile(r.content), save=True)
 
-        filename = Path(urlparse(url).path).name
-        output_path = page_image_path(img, filename)
-
-        # Make sure our directories exist
-        directory = Path(output_path).parent
-        directory.mkdir(parents=True, exist_ok=True)
-
-        # Write image data to our location
-        with Path(output_path).open("wb") as f:
-            f.write(r.content)
-
-        # Re-open the image as a Django File object
-        with Path(output_path).open("rb") as reopen:
-            new_file = File(reopen)
-            img.image.save(filename, new_file, save=True)
-
-        return self.image_url(output_path)
+        return img.image.url
 
     def find_image_paths(self, page):
         content = page.content.raw
diff --git a/apps/sponsors/management/commands/create_pycon_vouchers_for_sponsors.py b/apps/sponsors/management/commands/create_pycon_vouchers_for_sponsors.py
index 933670ce9..3b1cc9ed7 100644
--- a/apps/sponsors/management/commands/create_pycon_vouchers_for_sponsors.py
+++ b/apps/sponsors/management/commands/create_pycon_vouchers_for_sponsors.py
@@ -51,7 +51,7 @@ def api_call(uri, query):
 
     headers = {
         "X-API-Key": str(settings.PYCON_API_KEY),
-        "X-API-Signature": str(sha1(base_string.encode("utf-8")).hexdigest()),  # noqa: S324 - API signature, not for security storage
+        "X-API-Signature": str(sha1(base_string.encode("utf-8")).hexdigest()),  # noqa: S324 - required by PyCon API
         "X-API-Timestamp": str(timestamp),
     }
     scheme = "http" if settings.DEBUG else "https"
diff --git a/pydotorg/views.py b/pydotorg/views.py
index 53bcc76e8..2d609150a 100644
--- a/pydotorg/views.py
+++ b/pydotorg/views.py
@@ -4,7 +4,7 @@
 import json
 import re
 from collections import defaultdict
-from pathlib import Path
+from pathlib import Path, PurePosixPath
 
 from django.conf import settings
 from django.http import HttpResponse, JsonResponse
@@ -84,7 +84,11 @@ class MediaMigrationView(RedirectView):
 
     def get_redirect_url(self, *args, **kwargs):
         """Build the S3 redirect URL from the media path."""
-        image_path = kwargs["url"]
+        # Normalize path to prevent traversal (../, ....//,  %2e%2e/, etc.)
+        image_path = PurePosixPath(kwargs["url"]).as_posix().lstrip("/")
+        # Collapse any remaining parent references after normalization
+        parts = [p for p in image_path.split("/") if p not in (".", "..")]
+        image_path = "/".join(parts)
         if self.prefix:
             image_path = f"{self.prefix}/{image_path}"
         return f"{settings.AWS_S3_ENDPOINT_URL}/{settings.AWS_STORAGE_BUCKET_NAME}/{image_path}"
diff --git a/static/fonts/demo/demo.js b/static/fonts/demo/demo.js
index 6f45f1c40..3eb09052a 100644
--- a/static/fonts/demo/demo.js
+++ b/static/fonts/demo/demo.js
@@ -15,7 +15,7 @@ document.body.addEventListener("click", function(e) {
         testDrive = document.getElementById('testDrive'),
         testText = document.getElementById('testText');
     function updateTest() {
-        testDrive.innerHTML = testText.value || String.fromCharCode(160);
+        testDrive.textContent = testText.value || String.fromCharCode(160);
         if (window.icomoonLiga) {
             window.icomoonLiga(testDrive);
         }
diff --git a/static/js/sponsors/applicationForm.js b/static/js/sponsors/applicationForm.js
index bed84dd9b..2205b6900 100644
--- a/static/js/sponsors/applicationForm.js
+++ b/static/js/sponsors/applicationForm.js
@@ -1,5 +1,17 @@
 const DESKTOP_WIDTH_LIMIT = 1200;
 
+function isSafeImageSrc(url) {
+  if (!url) return false;
+  // Allow relative URLs starting with / (but not protocol-relative //)
+  if (url.charAt(0) === '/' && url.charAt(1) !== '/') return true;
+  try {
+    let parsed = new URL(url, window.location.origin);
+    return parsed.origin === window.location.origin;
+  } catch (e) {
+    return false;
+  }
+}
+
 $(document).ready(function(){
   const SELECTORS = {
     packageInput:  function() { return $("input[name=package]"); },
@@ -66,7 +78,9 @@ $(document).ready(function(){
         img.setAttribute('data-next-state', src);
       }
 
-      img.setAttribute('src', initImg);
+      if (isSafeImageSrc(initImg)) {
+        img.setAttribute('src', initImg);
+      }
     });
     $(".selected").removeClass("selected");
     $('.custom-fee').hide();
@@ -89,7 +103,9 @@ $(document).ready(function(){
         img.setAttribute('data-next-state', src);
       }
 
-      img.setAttribute('src', initImg);
+      if (isSafeImageSrc(initImg)) {
+        img.setAttribute('src', initImg);
+      }
     });
     $(".selected").removeClass("selected");
 
@@ -166,7 +182,9 @@ function benefitUpdate(benefitId, packageId) {
   const benefitsInputs = Array(...document.querySelectorAll('[data-benefit-id]'));
   const hiddenInput = benefitsInputs.filter((b) => b.getAttribute('data-benefit-id') == benefitId)[0];
   hiddenInput.checked = !hiddenInput.checked;
-  clickedImg.src = newSrc;
+  if (isSafeImageSrc(newSrc)) {
+    clickedImg.src = newSrc;
+  }
 
   // Check if there are any type of customization. If so, display custom-fee label.
   let pkgBenefits = Array(...document.getElementById(`package_benefits_${packageId}`).children).map(div => div.textContent).sort();