Parse Server has a session field immutability bypass via falsy-value guard

Impact

An authenticated user can bypass the immutability guard on session fields (expiresAt, createdWith) by sending a null value in a PUT request to the session update endpoint. This allows nullifying the session expiry, making the session valid indefinitely and bypassing configured session length policies.

Patches

The truthiness-based guard checks were replaced with key-presence checks that reject any value for protected session fields, including null.

Workarounds

There is no known workaround. A beforeSave trigger on _Session could be used to reject null values for expiresAt and createdWith.