From b7967cbb988809956f1da15f293c780bcd6a0f46 Mon Sep 17 00:00:00 2001
From: Nasim Uddin <64758014+Nasim25@users.noreply.github.com>
Date: Thu, 27 Nov 2025 01:14:33 +0600
Subject: [PATCH 1/3] Fix substrReplace to be multibyte safe

---
 src/Illuminate/Support/Str.php   | 4 +++-
 tests/Support/SupportStrTest.php | 6 ++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/Illuminate/Support/Str.php b/src/Illuminate/Support/Str.php
index 164018788683..8c2135d52315 100644
--- a/src/Illuminate/Support/Str.php
+++ b/src/Illuminate/Support/Str.php
@@ -1751,7 +1751,9 @@ public static function substrReplace($string, $replace, $offset = 0, $length = n
             $length = strlen($string);
         }
 
-        return substr_replace($string, $replace, $offset, $length);
+        return mb_substr($string, 0, $offset)
+            . $replace
+            . mb_substr($string, $offset + $length);
     }
 
     /**
diff --git a/tests/Support/SupportStrTest.php b/tests/Support/SupportStrTest.php
index a29252a0bff3..478f65b81269 100755
--- a/tests/Support/SupportStrTest.php
+++ b/tests/Support/SupportStrTest.php
@@ -1275,6 +1275,12 @@ public function testSubstrReplace()
         $this->assertSame('Laravel – The PHP Framework for Web Artisans', Str::substrReplace('Laravel Framework', '– The PHP Framework for Web Artisans', 8));
     }
 
+    public function testSubstrReplaceWithMultibyte()
+    {
+        $this->assertSame('kengä', Str::substrReplace('kenkä', 'ng', -3, 2));
+        $this->assertSame('kenga', Str::substrReplace('kenka', 'ng', -3, 2));
+    }
+
     public function testTake()
     {
         $this->assertSame('ab', Str::take('abcdef', 2));

From cd3ad36e74b3f0d11d8360d5ec95f62673c9681c Mon Sep 17 00:00:00 2001
From: Nasim Uddin <64758014+Nasim25@users.noreply.github.com>
Date: Thu, 27 Nov 2025 02:32:13 +0600
Subject: [PATCH 2/3] Apply code style fixes

---
 src/Illuminate/Support/Str.php | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/Illuminate/Support/Str.php b/src/Illuminate/Support/Str.php
index 8c2135d52315..bdfab9d27fae 100644
--- a/src/Illuminate/Support/Str.php
+++ b/src/Illuminate/Support/Str.php
@@ -1752,8 +1752,8 @@ public static function substrReplace($string, $replace, $offset = 0, $length = n
         }
 
         return mb_substr($string, 0, $offset)
-            . $replace
-            . mb_substr($string, $offset + $length);
+            .$replace
+            .mb_substr($string, $offset + $length);
     }
 
     /**

From 4bfb0b7e159777ed261f9f4a6615904dd68b78d1 Mon Sep 17 00:00:00 2001
From: Taylor Otwell <taylor@laravel.com>
Date: Thu, 27 Nov 2025 10:35:33 -0600
Subject: [PATCH 3/3] formatting

---
 src/Illuminate/Support/Str.php | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Illuminate/Support/Str.php b/src/Illuminate/Support/Str.php
index bdfab9d27fae..664d445f493b 100644
--- a/src/Illuminate/Support/Str.php
+++ b/src/Illuminate/Support/Str.php
@@ -1748,7 +1748,7 @@ public static function substrCount($haystack, $needle, $offset = 0, $length = nu
     public static function substrReplace($string, $replace, $offset = 0, $length = null)
     {
         if ($length === null) {
-            $length = strlen($string);
+            $length = static::length($string);
         }
 
         return mb_substr($string, 0, $offset)