Here is a summary of the text: A missing charset attribute in an HTTP response header can lead to severe Cross-Site Scripting (XSS) vulnerabilities. Browsers use various methods to determine the character encoding, including the Content-Type header, <meta> tags, and auto-detection through Byte-Order Marks. However, when these methods fail to detect a valid charset, browsers may resort to making educated guesses or using non-strict behavior, which can be exploited by attackers. The ISO-2022-JP character encoding is particularly vulnerable due to its escape sequences that allow switching between different character sets. Attackers can use two techniques to inject arbitrary JavaScript code: "Negating Backslash Escaping" and "Breaking HTML Context". The first technique involves inserting an escape sequence in a user-controlled string, while the second technique involves controlling values in multiple HTML contexts to break the HTML document's syntax. Providing charset information is essential to prevent these vulnerabilities, and browsers should consider disabling auto-detection for the ISO-2022-JP character encoding.