fix: harden encoded filter settings against malformed and stale input

public/typo3conf/ext/ep_products/Classes/Controller/SearchController.php

@@ -87,12 +87,16 @@ class SearchController extends ActionController
 
     public function initializeSearchresultAction()
     {
-        // Process encoded filtersettings from static search result
+        // Process encoded filtersettings from static search result.
+        // Explicit filter settings win: they carry the visitor's current selection,
+        // whereas a stale 'f' riding along on a link would silently replace it.
         $encodedFilterSettings = GeneralUtility::_GET('f');
-        if ($encodedFilterSettings) {
+        if ($encodedFilterSettings && !$this->request->hasArgument('filterSettings')) {
             $filterSettingsEncoder = new FilterSettingsEncoder();
             $filterSettings = $filterSettingsEncoder->decode($encodedFilterSettings);
-            $this->request->setArgument('filterSettings', $filterSettings);
+            if (count($filterSettings) > 0) {
+                $this->request->setArgument('filterSettings', $filterSettings);
+            }
         }
         $forcedConceptUids = GeneralUtility::intExplode(',', $this->settings['forcedConceptUids'], true);
         $this->processFilterSettingsArgument($forcedConceptUids);

public/typo3conf/ext/ep_products/Classes/Service/FilterSettingsEncoder.php

@@ -76,11 +76,28 @@ class FilterSettingsEncoder
         return implode('|', $encoded);
     }
 
+    /**
+     * Decodes an encoded filter settings string.
+     *
+     * The format is strictly positional, so a string whose field count does not
+     * match the mapping cannot be interpreted: every field after a missing one
+     * would be read into the wrong setting. Such input is rejected outright
+     * rather than silently producing a shifted - and therefore wrong - result.
+     *
+     * @param string $data
+     * @return array the decoded settings, or an empty array if $data is malformed
+     */
     public function decode(string $data): array
     {
-        $decoded = [];
+        $mapping = $this->getMapping();
         $values = explode('|', $data);
-        foreach ($this->getMapping() as $index => $property)
+
+        if (count($values) !== count($mapping)) {
+            return [];
+        }
+
+        $decoded = [];
+        foreach ($mapping as $index => $property)
         {
             [$name, $type] = $property;
             $value = $values[$index];