This is almost universally used, and occasionally the. PHP uses the include and require functions to include and execute code located in a separate file. For instance, the following code block prints “Hello, World!”: 1234 This means that an attacker can “break up” their code to evade scanners using comments. Multiline comments are particularly useful to malware authors because they are ignored by PHP, and do not have to extend over multiple lines. *, the beginning of a multiline comment, which can only closed with */. #, likewise a single line comment that ends on the next line, though this is less common than ‘//’. , denoting a single line comment that ends on the next line. Well-commented code is considered a best practice, as it makes it much easier to maintain software and pay off technical debt, but comments can also be used for illicit purposes. PHP has several methods of adding code comments that you may already be familiar with. Wordfence CLI in particular is useful in these cases, as it is highly performant and can run multithreaded jobs, compensating for any speed penalties imposed by these techniques. Several of the methods we will cover today, such as comment abuse, can be combined into almost infinite variations with minute changes, thus rendering them completely undetectable to traditional hash-based malware scanning and even partially slowing down regular expression-based scanning of the type used by Wordfence.įortunately, while these methods do make analysis more difficult, and can slow down scanning, their presence in certain combinations is a strong signal of malicious activity, and the malware detection signatures used by the Wordfence plugin and Wordfence CLI are tuned to detect these combinations with astoundingly few false positives. While it is not practical to cover every possible technique in active use, this article will detail the more commonly found methods, and help illustrate the wide range of possibilities when decoding obfuscated malware. Such simpler obfuscation methods can also be creatively combined with encoding techniques, granting malware authors a formidable array of tactics to avoid detection. These techniques are also often easier for a human analyst to spot, but they are also more difficult to detect using scanning tools due to the wide variety of permutations available. The techniques covered in this post are often simpler and “hackier” than the ones listed in the previous article, and most of them are less reliable as indicators of malicious activity individually, as several of them typically need to be combined in order to achieve sufficient obfuscation. One of the main contributing factors to the popularity of PHP is its ease of use, but the same functionality that makes it easy to use also makes it easy to abuse, often in ways that were never intended. In the first post in this series, we defined Obfuscation as the process of concealing the purpose or functionality of code or data so that it evades detection and is more difficult for a human or security software to analyze, but still fulfills its intended purpose. In today’s post, we’re going to dive a little bit deeper into other obfuscation techniques that make use of other features available in PHP. In the first post in this series, we covered common PHP encoding techniques and how they’re used by malware to hide from security analysts and scanners.
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