diff --git a/system/HTTP/SiteURIFactory.php b/system/HTTP/SiteURIFactory.php
index 11dccce6c540..6348b8464611 100644
--- a/system/HTTP/SiteURIFactory.php
+++ b/system/HTTP/SiteURIFactory.php
@@ -169,9 +169,11 @@ private function parseRequestURI(): string
             $this->superglobals->setServer('QUERY_STRING', $query);
         }
 
-        // Update our global GET for values likely to have been changed
+        // Refresh only the request values derived from superglobals after GET changes.
+        $previousRequestData = $this->superglobals->getRequestData();
         parse_str($this->superglobals->server('QUERY_STRING'), $get);
         $this->superglobals->setGetArray($get);
+        $this->refreshRequestAfterGetChange($previousRequestData);
 
         return URI::removeDotSegments($path);
     }
@@ -201,9 +203,11 @@ private function parseQueryString(): string
             $path = $query;
         }
 
-        // Update our global GET for values likely to have been changed
+        // Refresh only the request values derived from superglobals after GET changes.
+        $previousRequestData = $this->superglobals->getRequestData();
         parse_str($this->superglobals->server('QUERY_STRING'), $get);
         $this->superglobals->setGetArray($get);
+        $this->refreshRequestAfterGetChange($previousRequestData);
 
         return URI::removeDotSegments($path);
     }
@@ -222,6 +226,38 @@ private function createURIFromRoutePath(string $routePath): SiteURI
         return new SiteURI($this->appConfig, $relativePath, $this->getHost());
     }
 
+    /**
+     * Update REQUEST once during URI parsing, leaving application-defined values alone.
+     *
+     * @param array<array-key, mixed> $previousRequestData
+     */
+    private function refreshRequestAfterGetChange(array $previousRequestData): void
+    {
+        $request     = $this->superglobals->getRequestArray();
+        $currentData = $this->superglobals->getRequestData();
+
+        foreach ($previousRequestData as $key => $value) {
+            // A different value was supplied directly in REQUEST; preserve it.
+            if (! array_key_exists($key, $request) || $request[$key] !== $value) {
+                continue;
+            }
+
+            if (array_key_exists($key, $currentData)) {
+                $request[$key] = $currentData[$key];
+            } else {
+                unset($request[$key]);
+            }
+        }
+
+        foreach ($currentData as $key => $value) {
+            if (! array_key_exists($key, $previousRequestData) && ! array_key_exists($key, $request)) {
+                $request[$key] = $value;
+            }
+        }
+
+        $this->superglobals->setRequestArray($request);
+    }
+
     /**
      * @return string|null The current hostname. Returns null if no valid host.
      */
diff --git a/system/Superglobals.php b/system/Superglobals.php
index ac0ea289bd77..21909e432b0e 100644
--- a/system/Superglobals.php
+++ b/system/Superglobals.php
@@ -387,6 +387,51 @@ public function setRequestArray(array $array): self
         return $this;
     }
 
+    /**
+     * Returns the merged $_GET, $_POST, and $_COOKIE data according to the
+     * `request_order` (or `variables_order`) ini setting, without mutating
+     * $_REQUEST.
+     *
+     * PHP populates $_REQUEST only once at the start of the request. When
+     * $_GET is modified later (e.g. by SiteURIFactory), $_REQUEST becomes
+     * stale. This method returns the current merged values so callers can
+     * read up-to-date request data without relying on the stale $_REQUEST.
+     *
+     * @param string|null $requestOrder Overrides the `request_order` ini
+     *                                  setting. Useful for testing, since the
+     *                                  ini setting cannot be changed at runtime.
+     *
+     * @return array<string, request_items>
+     */
+    public function getRequestData(?string $requestOrder = null): array
+    {
+        $requestOrder ??= (string) ini_get('request_order');
+
+        if ($requestOrder === '') {
+            $requestOrder = (string) ini_get('variables_order');
+        }
+
+        if ($requestOrder === '') {
+            $requestOrder = 'GP';
+        }
+
+        $request = [];
+
+        foreach (array_unique(str_split(strtoupper($requestOrder))) as $type) {
+            match ($type) {
+                // array_replace_recursive() matches PHP's own $_REQUEST merge
+                // (php_autoglobal_merge): numeric keys are preserved and
+                // array values are merged recursively.
+                'G'     => $request = array_replace_recursive($request, $this->get),
+                'P'     => $request = array_replace_recursive($request, $this->post),
+                'C'     => $request = array_replace_recursive($request, $this->cookie),
+                default => null,
+            };
+        }
+
+        return $request;
+    }
+
     /**
      * Get all $_FILES values.
      *
diff --git a/tests/system/HTTP/SiteURIFactoryDetectRoutePathTest.php b/tests/system/HTTP/SiteURIFactoryDetectRoutePathTest.php
index 4bc29fbecc4d..07509eeb2a73 100644
--- a/tests/system/HTTP/SiteURIFactoryDetectRoutePathTest.php
+++ b/tests/system/HTTP/SiteURIFactoryDetectRoutePathTest.php
@@ -258,6 +258,70 @@ public function testQueryStringWithQueryString(): void
         $this->assertSame(['code' => 'good'], $_GET);
     }
 
+    public function testQueryStringRefreshesRequestWithoutOverwritingCustomValues(): void
+    {
+        $superglobals = new Superglobals(
+            [
+                'REQUEST_URI'  => '/index.php?/ci/woot?code=good',
+                'QUERY_STRING' => '/ci/woot?code=good',
+                'SCRIPT_NAME'  => '/index.php',
+            ],
+            ['/ci/woot?code' => 'good', 'override' => 'from get'],
+            ['posted' => 'post'],
+            [],
+            [],
+            [
+                '/ci/woot?code' => 'good',
+                'override'      => 'custom',
+                'posted'        => 'post',
+                'unrelated'     => 'keep',
+            ],
+        );
+        Services::injectMock('superglobals', $superglobals);
+
+        $factory = new SiteURIFactory(new App(), $superglobals);
+
+        $this->assertSame('ci/woot', $factory->detectRoutePath('QUERY_STRING'));
+        $this->assertSame([
+            'override'  => 'custom',
+            'posted'    => 'post',
+            'unrelated' => 'keep',
+            'code'      => 'good',
+        ], $superglobals->getRequestArray());
+        $this->assertSame($superglobals->getRequestArray(), $_REQUEST);
+
+        $superglobals->setGet('code', 'later');
+
+        $this->assertSame('good', $superglobals->request('code'));
+    }
+
+    public function testRequestURIRefreshesRequestForValidation(): void
+    {
+        $superglobals = new Superglobals(
+            [
+                'REQUEST_URI' => '/index.php/woot?code=good',
+                'SCRIPT_NAME' => '/index.php',
+            ],
+            ['code' => 'stale'],
+            [],
+            [],
+            [],
+            ['code' => 'stale', 'unrelated' => 'keep'],
+        );
+        Services::injectMock('superglobals', $superglobals);
+
+        $config  = new App();
+        $factory = new SiteURIFactory($config, $superglobals);
+
+        $this->assertSame('woot', $factory->detectRoutePath('REQUEST_URI'));
+        $this->assertSame(['code' => 'good', 'unrelated' => 'keep'], $superglobals->getRequestArray());
+
+        $request = new IncomingRequest($config, new SiteURI($config), null, new UserAgent());
+
+        $this->assertSame('good', $request->getVar('code'));
+        $this->assertTrue(service('validation')->withRequest($request)->setRules(['code' => 'in_list[good]'])->run());
+    }
+
     public function testQueryStringEmpty(): void
     {
         // /index.php?
diff --git a/tests/system/SuperglobalsTest.php b/tests/system/SuperglobalsTest.php
index e4b8b23b2b28..2f4d0cab1ea0 100644
--- a/tests/system/SuperglobalsTest.php
+++ b/tests/system/SuperglobalsTest.php
@@ -302,6 +302,106 @@ public function testRequestSetArray(): void
         $this->assertSame($data, $_REQUEST);
     }
 
+    public function testGetRequestDataMergesGetAndPost(): void
+    {
+        $this->superglobals->setGetArray(['get_key' => 'get_value']);
+        $this->superglobals->setPostArray(['post_key' => 'post_value']);
+
+        $data = $this->superglobals->getRequestData();
+
+        $this->assertSame('get_value', $data['get_key']);
+        $this->assertSame('post_value', $data['post_key']);
+    }
+
+    public function testGetRequestDataReflectsGetChanges(): void
+    {
+        $this->superglobals->setGetArray(['key' => 'old']);
+
+        $this->assertSame('old', $this->superglobals->getRequestData()['key']);
+
+        // Simulate SiteURIFactory updating $_GET after the request started.
+        $this->superglobals->setGetArray(['key' => 'new']);
+
+        $this->assertSame('new', $this->superglobals->getRequestData()['key']);
+    }
+
+    public function testGetRequestDataMergesCookie(): void
+    {
+        $this->superglobals->setGetArray(['get_key' => 'get_value']);
+        $this->superglobals->setPostArray(['post_key' => 'post_value']);
+        $this->superglobals->setCookieArray(['cookie_key' => 'cookie_value']);
+
+        $data = $this->superglobals->getRequestData('GPC');
+
+        $this->assertSame('get_value', $data['get_key']);
+        $this->assertSame('post_value', $data['post_key']);
+        $this->assertSame('cookie_value', $data['cookie_key']);
+    }
+
+    public function testGetRequestDataRespectsOrder(): void
+    {
+        $this->superglobals->setGetArray(['shared' => 'get']);
+        $this->superglobals->setPostArray(['shared' => 'post']);
+        $this->superglobals->setCookieArray(['shared' => 'cookie']);
+
+        // Later sources overwrite earlier ones, matching PHP's request_order.
+        $this->assertSame('post', $this->superglobals->getRequestData('GP')['shared']);
+        $this->assertSame('cookie', $this->superglobals->getRequestData('GPC')['shared']);
+        $this->assertSame('get', $this->superglobals->getRequestData('PG')['shared']);
+    }
+
+    public function testGetRequestDataEmptyOrderFallsBackToVariablesOrder(): void
+    {
+        $this->superglobals->setGetArray(['get' => 'value']);
+        $this->superglobals->setPostArray(['post' => 'value']);
+        $this->superglobals->setCookieArray(['cookie' => 'value']);
+
+        $this->assertSame(
+            $this->superglobals->getRequestData((string) ini_get('variables_order')),
+            $this->superglobals->getRequestData(''),
+        );
+    }
+
+    public function testGetRequestDataNormalizesOrderAndIgnoresDuplicates(): void
+    {
+        $this->superglobals->setGetArray(['shared' => 'get']);
+        $this->superglobals->setPostArray(['shared' => 'post']);
+        $this->superglobals->setCookieArray(['shared' => 'cookie']);
+
+        $this->assertSame('post', $this->superglobals->getRequestData('gp')['shared']);
+        $this->assertSame('post', $this->superglobals->getRequestData('GPG')['shared']);
+        $this->assertSame('cookie', $this->superglobals->getRequestData('gPcGpC')['shared']);
+    }
+
+    public function testGetRequestDataIgnoresUnknownOrderTypes(): void
+    {
+        $this->superglobals->setGetArray(['get_key' => 'get_value']);
+
+        $data = $this->superglobals->getRequestData('GX');
+
+        $this->assertSame(['get_key' => 'get_value'], $data);
+    }
+
+    public function testGetRequestDataPreservesNumericKeys(): void
+    {
+        parse_str('100=foo', $get);
+        $this->superglobals->setGetArray($get);
+
+        $data = $this->superglobals->getRequestData('G');
+
+        $this->assertSame([100 => 'foo'], $data);
+    }
+
+    public function testGetRequestDataMergesRecursively(): void
+    {
+        $this->superglobals->setGetArray(['a' => ['x' => 'get']]);
+        $this->superglobals->setPostArray(['a' => ['y' => 'post']]);
+
+        $data = $this->superglobals->getRequestData('GP');
+
+        $this->assertSame(['a' => ['x' => 'get', 'y' => 'post']], $data);
+    }
+
     // $_FILES tests
     public function testFilesGetArray(): void
     {
diff --git a/user_guide_src/source/changelogs/v4.7.5.rst b/user_guide_src/source/changelogs/v4.7.5.rst
index 0897a791ba7c..0bf28cccc23e 100644
--- a/user_guide_src/source/changelogs/v4.7.5.rst
+++ b/user_guide_src/source/changelogs/v4.7.5.rst
@@ -63,6 +63,7 @@ Bugs Fixed
 - **Helpers:** Fixed a bug where ``get_dir_file_info()`` returned incomplete entries for subdirectories and missing files instead of omitting them.
 - **Helpers:** Fixed a bug where ``word_wrap()`` entered an infinite loop when the character limit was below 2. Over-length words are now kept whole in that case.
 - **Honeypot:** Fixed a bug where bot detection returned an HTTP 500 response instead of 403 (Forbidden).
+- **HTTP:** Fixed stale ``$_REQUEST`` values after ``SiteURIFactory`` normalizes GET parameters, so ``Validation::withRequest()`` reads the normalized values while unrelated REQUEST entries are preserved.
 - **I18n:** Fixed a bug where ``Time::today()``, ``Time::yesterday()``, and ``Time::tomorrow()`` ignored the specified ``$timezone`` and ``setTestNow()`` when calculating the day.
 - **Logger:** Fixed a bug where interpolating a log message with array or non-stringable context values could raise PHP warnings or errors.
 - **Validation:** Fixed a bug where ``valid_cc_number`` accepted non-digit characters (e.g., a decimal point) in the card number. Such values could pass the Luhn check and triggered an ``Undefined array key`` warning inside it; the number is now checked with ``ctype_digit()``.