diff --git a/wp-includes/sodium_compat/composer.json b/wp-includes/sodium_compat/composer.json
index 160d94490b..cf55d79042 100644
--- a/wp-includes/sodium_compat/composer.json
+++ b/wp-includes/sodium_compat/composer.json
@@ -54,7 +54,7 @@
     "paragonie/random_compat": ">=1"
   },
   "require-dev": {
-    "phpunit/phpunit": "^3|^4|^5|^6|^7"
+    "phpunit/phpunit": "^3|^4|^5|^6|^7|^8|^9"
   },
   "suggest": {
     "ext-libsodium": "PHP < 7.0: Better performance, password hashing (Argon2i), secure memory management (memzero), and better security.",
diff --git a/wp-includes/sodium_compat/src/Core/SipHash.php b/wp-includes/sodium_compat/src/Core/SipHash.php
index 7d3981620e..542b4cc2e4 100644
--- a/wp-includes/sodium_compat/src/Core/SipHash.php
+++ b/wp-includes/sodium_compat/src/Core/SipHash.php
@@ -14,8 +14,9 @@ class ParagonIE_Sodium_Core_SipHash extends ParagonIE_Sodium_Core_Util
     /**
      * @internal You should not use this directly from another application
      *
-     * @param int[] $v
-     * @return int[]
+     * @param array<array-key, int> $v
+     * @return array<array-key, int>
+     *
      */
     public static function sipRound(array $v)
     {
@@ -26,27 +27,27 @@ class ParagonIE_Sodium_Core_SipHash extends ParagonIE_Sodium_Core_Util
         );
 
         #  v1=ROTL(v1,13);
-        list($v[2], $v[3]) = self::rotl_64($v[2], $v[3], 13);
+        list($v[2], $v[3]) = self::rotl_64((int) $v[2], (int) $v[3], 13);
 
         #  v1 ^= v0;
-        $v[2] ^= $v[0];
-        $v[3] ^= $v[1];
+        $v[2] = (int) $v[2] ^ (int) $v[0];
+        $v[3] = (int) $v[3] ^ (int) $v[1];
 
         #  v0=ROTL(v0,32);
         list($v[0], $v[1]) = self::rotl_64((int) $v[0], (int) $v[1], 32);
 
         # v2 += v3;
         list($v[4], $v[5]) = self::add(
-            array($v[4], $v[5]),
-            array($v[6], $v[7])
+            array((int) $v[4], (int) $v[5]),
+            array((int) $v[6], (int) $v[7])
         );
 
         # v3=ROTL(v3,16);
-        list($v[6], $v[7]) = self::rotl_64($v[6], $v[7], 16);
+        list($v[6], $v[7]) = self::rotl_64((int) $v[6], (int) $v[7], 16);
 
         #  v3 ^= v2;
-        $v[6] ^= $v[4];
-        $v[7] ^= $v[5];
+        $v[6] = (int) $v[6] ^ (int) $v[4];
+        $v[7] = (int) $v[7] ^ (int) $v[5];
 
         # v0 += v3;
         list($v[0], $v[1]) = self::add(
@@ -58,8 +59,8 @@ class ParagonIE_Sodium_Core_SipHash extends ParagonIE_Sodium_Core_Util
         list($v[6], $v[7]) = self::rotl_64((int) $v[6], (int) $v[7], 21);
 
         # v3 ^= v0;
-        $v[6] ^= $v[0];
-        $v[7] ^= $v[1];
+        $v[6] = (int) $v[6] ^ (int) $v[0];
+        $v[7] = (int) $v[7] ^ (int) $v[1];
 
         # v2 += v1;
         list($v[4], $v[5]) = self::add(
@@ -71,8 +72,8 @@ class ParagonIE_Sodium_Core_SipHash extends ParagonIE_Sodium_Core_Util
         list($v[2], $v[3]) = self::rotl_64((int) $v[2], (int) $v[3], 17);
 
         #  v1 ^= v2;;
-        $v[2] ^= $v[4];
-        $v[3] ^= $v[5];
+        $v[2] = (int) $v[2] ^ (int) $v[4];
+        $v[3] = (int) $v[3] ^ (int) $v[5];
 
         # v2=ROTL(v2,32)
         list($v[4], $v[5]) = self::rotl_64((int) $v[4], (int) $v[5], 32);
diff --git a/wp-includes/sodium_compat/src/Core/Util.php b/wp-includes/sodium_compat/src/Core/Util.php
index aa93dfd044..3bb4dafb30 100644
--- a/wp-includes/sodium_compat/src/Core/Util.php
+++ b/wp-includes/sodium_compat/src/Core/Util.php
@@ -903,6 +903,9 @@ abstract class ParagonIE_Sodium_Core_Util
      *
      * @internal You should not use this directly from another application
      *
+     * Note: MB_OVERLOAD_STRING === 2, but we don't reference the constant
+     * (for nuisance-free PHP 8 support)
+     *
      * @return bool
      */
     protected static function isMbStringOverride()
@@ -913,7 +916,8 @@ abstract class ParagonIE_Sodium_Core_Util
             $mbstring = extension_loaded('mbstring')
                 && defined('MB_OVERLOAD_STRING')
                 &&
-            ((int) (ini_get('mbstring.func_overload')) & MB_OVERLOAD_STRING);
+            ((int) (ini_get('mbstring.func_overload')) & 2);
+            // MB_OVERLOAD_STRING === 2
         }
         /** @var bool $mbstring */
 
diff --git a/wp-includes/sodium_compat/src/File.php b/wp-includes/sodium_compat/src/File.php
index b4948db36c..867da3b9a9 100644
--- a/wp-includes/sodium_compat/src/File.php
+++ b/wp-includes/sodium_compat/src/File.php
@@ -243,6 +243,7 @@ class ParagonIE_Sodium_File extends ParagonIE_Sodium_Core_Util
             ParagonIE_Sodium_Compat::memzero($nonce);
             ParagonIE_Sodium_Compat::memzero($ephKeypair);
         } catch (SodiumException $ex) {
+            /** @psalm-suppress PossiblyUndefinedVariable */
             unset($ephKeypair);
         }
         return $res;
@@ -541,6 +542,7 @@ class ParagonIE_Sodium_File extends ParagonIE_Sodium_Core_Util
         try {
             ParagonIE_Sodium_Compat::memzero($key);
         } catch (SodiumException $ex) {
+            /** @psalm-suppress PossiblyUndefinedVariable */
             unset($key);
         }
         return $res;
diff --git a/wp-includes/sodium_compat/src/PHP52/SplFixedArray.php b/wp-includes/sodium_compat/src/PHP52/SplFixedArray.php
index 9279f60c1e..c333ad4fad 100644
--- a/wp-includes/sodium_compat/src/PHP52/SplFixedArray.php
+++ b/wp-includes/sodium_compat/src/PHP52/SplFixedArray.php
@@ -102,6 +102,7 @@ class SplFixedArray implements Iterator, ArrayAccess, Countable
      */
     public function offsetGet($index)
     {
+        /** @psalm-suppress MixedReturnStatement */
         return $this->internalArray[(int) $index];
     }
 
@@ -142,6 +143,7 @@ class SplFixedArray implements Iterator, ArrayAccess, Countable
      */
     public function current()
     {
+        /** @psalm-suppress MixedReturnStatement */
         return current($this->internalArray);
     }
 
diff --git a/wp-includes/version.php b/wp-includes/version.php
index a44d879497..a425ea1c0b 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.6-RC2-49740';
+$wp_version = '5.6-RC2-49742';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.