A vulnerability in which a web application outputs user input into HTML as is, so that a script contained in the input runs in visitors' browsers as a page of that site. Escaping characters with special meaning on output is the fundamental countermeasure.
Japanese name: クロスサイトスクリプティング(XSS)
Cross-site scripting (XSS) appears in 4 practice questions across 2 topics, including Web Technology Basics, Information Security Basics.
Field: Information Security Basics
Answer: A. localStorage data is not attached to requests automatically; the JavaScript of pages of the same origin reads and writes it
localStorage is a storage area in the browser that keeps string keys and values per origin; it has no way to set an expiry and generally remains until deleted. It is not sent to the server automatically, so to send it, JavaScript puts it into a request. Cookies are small, generally up to about 4 KB each, and are sent automatically with every request, whereas larger data can be kept in localStorage. However, the page's JavaScript can read it at any time, so if there is an XSS flaw its contents can be stolen. This risk must be considered when storing values used for authentication.
Answer: B. Cross-site scripting (XSS). Escape characters with special meaning, such as < and >, when outputting posted text as HTML
Cross-site scripting (XSS) is a vulnerability in which a web application outputs user input into HTML as is, so a script contained in the input runs in visitors' browsers as part of the page. Because the script runs as a page of that site, it may steal the visitor's session information (cookies) or display fake input fields. The fundamental countermeasure is to escape characters with special meaning, such as <, >, & and quotation marks, according to where they are output (for example, converting < to <) so they are displayed as plain characters. Supplementary measures include giving cookies the HttpOnly attribute so scripts cannot read them, and restricting which scripts may run with a Content Security Policy. HTTPS protects the communication channel and cannot prevent a script embedded in a legitimate page from running.
With the HttpOnly attribute, the page's JavaScript cannot read it through document.cookie and the like, which reduces the damage if a session ID would otherwise be stolen through XSS.
Which of the following correctly describes the cookie set b…However, the page's JavaScript can read it at any time, so if there is an XSS flaw its contents can be stolen.
Which of the following correctly describes a difference bet…Cross-site scripting (XSS) is a vulnerability in which a web application outputs user input into HTML as is, so a script contained in the input runs in visitors' browsers as part of the page.
A bulletin-board web application had a vulnerability in whi…The difference from XSS is that XSS embeds a malicious script in the site, whereas CSRF makes the user's browser send legitimate-looking requests.
A web application has a vulnerability in which, if a logged…As an Amazon Associate I earn from qualifying purchases.
Cookie (HTTP cookie) Digital signature Hash function Message authentication code Multi-factor authentication Phishing Principle of least privilege Public-key cryptography Ransomware Salt