Spectre can give you read-access to the browser process via Javascript, yes, as they described in the original article: https://spectreattack.com/spectre.pdf ht

Spectre can give you read-access to the browser process via Javascript, yes, as they described in the original article: https://spectreattack.com/spectre.pdf https://spectreattack.com/spectre.pdf (section 4.3 on page 6). No write access, or access to the OS internals.