![]() ![]() “This approach cannot be detected through syntax highlighting as invisible characters are not shown at all and therefore are not colorized by the IDE/text editor,” he added. Similarly, when the checkCommands array is constructed, this hidden variable makes it into the array, whose constituent elements are passed to the exec function, which duly executes OS commands.Īn attacker could execute arbitrary OS commands by passing the “ㅤ” parameter to the endpoint in its URL-encoded form, said Ettlinger. Ī destructuring assignment retrieves from req.query the timeout and “ㅤ” parameters, and if passed the “ㅤ” is assigned to the invisible variable, explained Ettlinger. The following code snippet visualizes how the invisible character could pass unnoticed by replacing the character in question with its escape sequence representation: const = req.query. RECOMMENDED ‘Focus on brilliance at the basics’ – GitHub CSO Mike Hanley on shifting left and securing the software supply chain Resolving to implant a backdoor that trails no evidence of its presence, the researchers chose “ㅤ” (called a ‘HANGUL FILLER’) as their invisible Unicode character because it has the ID_Start property and can therefore appear in a JavaScript variable. The hacking technique was inspired by a Subreddit post documenting a developer’s struggles to identify a syntax error resulting from an invisible Unicode character hidden in JavaScript source code. Inherently effective at obfuscating code, “Unicode should be kept in mind when doing reviews of code from unknown or untrusted contributors” – something particularly applicable to open source projects, said Wolfgang Ettlinger, security researcher at Austrian cybersecurity firm Certitude Consulting, in a blog post. Security researchers have detailed how backdoors can be concealed within JavaScript by Unicode characters that are either invisible or readily confused with other characters.Īs a result, they contend, malicious code can evade detection during even otherwise thorough code reviews. Researchers urge developers to secure code by disallowing non-ASCII characters
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