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Date: Thu, 17 Jan 2019 22:50:08 -0200
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To: Marco Pivetta <ocramius@gmail.com>
Cc: internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] Unserializes, inheritance and allows_classes
From: marcospassos.com@gmail.com (Marcos Passos)

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Hi Marco,

Also: nothing denies an attacker from defining a subtype to your class,
> then passing a malicious instance to your application.


Fact, but it also reveals a fragility in the solution in the sense that one
has to opt between flexible design or security.

Em qui, 17 de jan de 2019 =C3=A0s 22:24, Marco Pivetta <ocramius@gmail.com>
escreveu:

>
> On Fri, Jan 18, 2019 at 12:49 AM Marcos Passos <marcospassos.com@gmail.co=
m>
> wrote:
>
>> Hi internals,
>>
>> Today I stumbled upon a limitation when implementing the unserialize
>> method
>> of a serializable class which depends on an abstraction also serializabl=
e.
>> Currently, there is no way to unserialize an object specifying a parent
>> class in the allowed_classes option:
>>
>> class SerializableBase implements \Serializable {
>> > }
>> > class SerializableChild extends SerializableBase {
>> > }
>> > class Foo implements \Serializable {
>> >    private $dependency;
>> >     public function __construct(SerializableBase $dependency) {
>> >         $this->dependency =3D $dependency;
>> >     }
>> >     public function serialize() : string {
>> >          return \serialize($this->dependency);
>> >     }
>> >    public function unserialize($data) : void {
>> >         $this->dependency =3D \unserialize($data, ['allowed_classes' =
=3D>
>> > SerializableBase::class]);
>> >    }
>> > }
>>
>>
>> Is this an intentional limitation?
>>
>>
> Seems expected to me: `allowed_classes` is a whitelist, not a complex
> filter/ruleset.
>
> Also: nothing denies an attacker from defining a subtype to your class,
> then passing a malicious instance to your application.
>
> Marco Pivetta
>
> http://twitter.com/Ocramius
>
> http://ocramius.github.com/
>
>

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