Fetch Metadata

XS-Search

October 1, 2020
Category Attack, Attack Principle
Defenses Fetch Metadata, SameSite Cookies

Cross-site search (XS-Search) is an important attack and principle in the family of XS-Leaks. The attack abuses Query-Based Search Systems to leak user information from an attacker origin 1 2. The original attack used timing measurements to detect whether or not a search system returned results and works as follows: Establish a baseline time for a request returning results (hit) and a baseline for a request with no results (miss). ...

CORB Leaks

October 1, 2020
Abuse Browser Feature, Error Events, Content-Type, nosniff
Category Attack
Defenses Fetch Metadata, SameSite Cookies

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). info ...

CORP Leaks

October 1, 2020
Abuse Browser Feature
Category Attack
Defenses Fetch Metadata, SameSite Cookies

Explanation # Cross-Origin Resource Policy (CORP) is a web platform security feature that allows websites to prevent certain resources from being loaded by other origins. This protection complements CORB since it is an opt-in defense, whereas CORB blocks some cross-origin reads by default. Unfortunately, similar to CORB, applications can introduce a new XS-Leak if they misconfigure the use of this protection. A webpage will introduce an XS-Leak if CORP is enforced based on user data. ...

Error Events

October 1, 2020
Abuse Error Events, Status Code, nosniff, Content-Type
Category Attack
Defenses Fetch Metadata, SameSite Cookies

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. ...

Frame Counting

October 1, 2020
Abuse iframes
Category Attack
Defenses Fetch Metadata, SameSite Cookies, COOP, Framing Protections

Window references allow cross-origin pages to get access to some of the attributes of other pages. These references become available when using or allowing iframe and window.open. The references provide (limited) information about the window as they still respect the same-origin policy. One of the accessible attributes is window.length which provides the number of frames in the window. This attribute can provide valuable information about a page to an attacker. ...

Navigations

October 1, 2020
Abuse Downloads, History, CSP Violations, Redirects, window.open, iframes
Category Attack
Defenses Fetch Metadata, SameSite Cookies, COOP, Framing Protections

Detecting if a cross-site page triggered a navigation (or didn’t) can be useful to an attacker. For example, a website may trigger a navigation in a certain endpoint depending on the status of the user. To detect if any kind of navigation occurred, an attacker can: Use an iframe and count the number of times the onload event is triggered. Check the value of history.length, which is accessible through any window reference. ...

Network Timing

October 1, 2020
Abuse iframes
Category Attack
Defenses Fetch Metadata, SameSite Cookies, COOP, Framing Protections

Network Timing side-channels have been present on the web since its beginning 1 2. These attacks have had different levels of impact over time, gaining new attention when browsers started shipping high precision timers like performance.now(). To obtain timing measurements attackers must use a clock, either an implicit or explicit one. These clocks are usually interchangeable for the purposes of XS-Leaks and only vary in accuracy and availability. For simplicity, this article will assume use of the performance. ...

Execution Timing

October 1, 2020
Abuse Event Loop, Service Workers, Site Isolation, CSS Injections, Regex Injections, iframes
Category Attack
Defenses Fetch Metadata, SameSite Cookies, COOP, Framing Protections

Measuring the time of JavaScript execution in a browser can give attackers information on when certain events are triggered, and how long some operations take. Timing the Event Loop # JavaScript’s concurrency model is based on a single-threaded event loop which means it can only run one task at a time. If, for example, some time-consuming task blocks the event loop, the user can perceive a freeze on a page as a result of the UI thread being starved. ...

Hybrid Timing

October 1, 2020
Abuse iframes
Category Attack
Defenses Fetch Metadata, SameSite Cookies, COOP

Hybrid Timing Attacks allow attackers to measure the sum of a bunch of factors that influence the final timing measurement. These factors include: Network delays Document parsing Retrieval and processing of subresources Code execution Some of the factors differ in value depending on the application. This means that Network Timing might be more significant in pages with more backend processing while Execution Timing can be more significant in applications processing and displaying data within the browser. ...

ID Attribute

October 1, 2020
Abuse onblur, focus, iframes
Category Attack
Defenses Fetch Metadata, SameSite Cookies, Framing Protections

The id attribute is widely used to identify HTML elements. Unfortunately, cross-origin websites can determine whether a given id is set anywhere on a page by leveraging the focus event and URL fragments. If https://example.com/foo#bar is loaded, the browser attempts to scroll to the element with id="bar". This can be detected cross-origin by loading https://example.com/foo#bar in an iframe; if there is an element with id="bar", the focus event fires. The blur event can also be used for the same purpose 1. ...