fix(misc): Handle cache unpickling failure in release check

Guard `cache.get('latest_release')` during release checks to prevent a
500 when stale cached data can't be unpickled after dependency upgrades.
On failure, log at debug level and delete the affected cache key.

Fixes #21254

netbox/extras/events.py

@@ -86,7 +86,7 @@ def enqueue_event(queue, instance, request, event_type):
 
 
 def process_event_rules(event_rules, object_type, event_type, data, username=None, snapshots=None, request=None):
-    user = User.objects.get(username=username) if username else None
+    user = None  # To be resolved from the username if needed
 
     for event_rule in event_rules:
 
@@ -134,6 +134,10 @@ def process_event_rules(event_rules, object_type, event_type, data, username=Non
             # Resolve the script from action parameters
             script = event_rule.action_object.python_class()
 
+            # Retrieve the User if not already resolved
+            if user is None:
+                user = User.objects.get(username=username)
+
             # Enqueue a Job to record the script's execution
             from extras.jobs import ScriptJob
             params = {

netbox/netbox/views/misc.py

@@ -1,5 +1,6 @@
 import re
 from collections import namedtuple
+import logging
 
 from django.conf import settings
 from django.contrib import messages
@@ -28,6 +29,8 @@ __all__ = (
     'SearchView',
 )
 
+logger = logging.getLogger(f'netbox.{__name__}')
+
 Link = namedtuple('Link', ('label', 'viewname', 'permission', 'count'))
 
 
@@ -50,7 +53,14 @@ class HomeView(ConditionalLoginRequiredMixin, View):
         # Check whether a new release is available. (Only for superusers.)
         new_release = None
         if request.user.is_superuser:
-            latest_release = cache.get('latest_release')
+            # cache.get() can raise if the cached value can't be unpickled after dependency upgrades
+            try:
+                latest_release = cache.get('latest_release')
+            except Exception:
+                logger.debug("Failed to read 'latest_release' from cache; deleting key", exc_info=True)
+                cache.delete('latest_release')
+                latest_release = None
+
             if latest_release:
                 release_version, release_url = latest_release
                 if release_version > version.parse(settings.RELEASE.version):