Core/Toolbox/Strings/IsSerialized.php
function isSerialized(): bool
    {
        // Empty strings cannot get unserialized
        if (strlen($this->string) <= 1) {
            return false;
        }

        // Serialized false, return true. unserialize() returns false on an
        // invalid string or it could return false if the string is serialized
        // false, eliminate that possibility.
        if ($this->string === 'b:0;') {
            $result = false;
            return true;
        }

        $length = strlen($this->string);
        $end = '';

        switch ($this->string[0]) {
            case 's':
                if ($this->string[$length - 2] !== '"') {
                    return false;
                }
            case 'b':
            case 'i':
            case 'd':
                $end .= ';';
            case 'a':
            case 'O':
                $end .= '}';

                if ($this->string[1] !== ':') {
                    return false;
                }

                switch ($this->string[2]) {
                    case 0:
                    case 1:
                    case 2:
                    case 3:
                    case 4:
                    case 5:
                    case 6:
                    case 7:
                    case 8:
                    case 9:
                        break;

                    default:
                        return false;
                }
            case 'N':
                $end .= ';';

                if ($this->string[$length - 1] !== $end[0]) {
                    return false;
                }

                break;

            default:
                return false;
        }

        if (($this->result = @unserialize($this->string)) === false) {
            $this->result = null;
            return false;
        }

        return true;
    }
function isSerialized(): bool
    {
        // Empty strings cannot get unserialized
        if (strlen($this->string) <= 1) {
            return false;
        }

        // Serialized false, return true. unserialize() returns false on an
        // invalid string or it could return false if the string is serialized
        // false, eliminate that possibility.
        if ($this->string === 'b:0;') {
            $result = false;
            return true;
        }

        $length = strlen($this->string);
        $end = '';

        switch ($this->string[0]) {
            case 's':
                if ($this->string[$length - 2] !== '"') {
                    return false;
                }
            case 'b':
            case 'i':
            case 'd':
                $end .= ';';
            case 'a':
            case 'O':
                $end .= '}';

                if ($this->string[1] !== ':') {
                    return false;
                }

                switch ($this->string[2]) {
                    case 0:
                    case 1:
                    case 2:
                    case 3:
                    case 4:
                    case 5:
                    case 6:
                    case 7:
                    case 8:
                    case 9:
                        break;

                    default:
                        return false;
                }
            case 'N':
                $end .= ';';

                if ($this->string[$length - 1] !== $end[0]) {
                    return false;
                }

                break;

            default:
                return false;
        }

        if (($this->result = @unserialize($this->string)) === false) {
            $this->result = null;
            return false;
        }

        return true;
    }
Tests if an input is valid PHP serialized string

Checks if a string is serialized using quick string manipulation
to throw out obviously incorrect strings. Unserialize is then run
on the string to perform the final verification.

Valid serialized forms are the following:
<ul>
<li>boolean: <code>b:1;</code></li>
<li>integer: <code>i:1;</code></li>
<li>double: <code>d:0.2;</code></li>
<li>string: <code>s:4:"test";</code></li>
<li>array: <code>a:3:{i:0;i:1;i:1;i:2;i:2;i:3;}</code></li>
<li>object: <code>O:8:"stdClass":0:{}</code></li>
<li>null: <code>N;</code></li>
</ul>

@return boolean if $value is serialized data, otherwise false