October 1, 2020
Cross-Origin Read Blocking (CORB) is a web platform security feature aimed at reducing the impact of speculative side-channel attacks such as Spectre. Unfortunately, blocking certain types of requests introduced a new type of XS-Leaks 1 that allows attackers to detect if CORB was enforced on one request, but wasn’t on another. Nevertheless, the introduced XS-Leaks are much less problematic than the issues actively protected by CORB (e.g. Spectre).
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This is a known issue in Chromium, and while it might remain unfixed, its impact is greatly reduced by the rollout of SameSite Cookies by default in Chromium-based browsers.
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October 1, 2020
When a webpage issues a request to a server (e.g. fetch, HTML tags), the server receives and processes this request. When received, the server decides whether the request should succeed (e.g. 200) or fail (e.g. 404) based on the provided context. When a response has an error status, an error event is fired by the browser for the page to handle. These errors also cover situations where the parser fails, for example when trying to embed HTML content as an image.
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The principle of Cache Probing consists of detecting whether a resource was cached by the browser. The concept has been known since the beginning of the web 1 and initially relied on detecting timing differences.
When a user visits a website, some resources such as images, scripts, and HTML content are fetched and later cached by the browser (under certain conditions). This optimization makes future navigations faster as the browser serves those resources from disk instead of requesting them again.
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