Obfuscation: There Are Two Sides To Everything

How to detect and prevent attackers from using these various techniques

Obfuscation is an important technique for protecting software that also carries risks, especially when used by malware authors. In this article, we examine obfuscation, its effects, and responses to it.

What Is Obfuscation?

Obfuscation is the technique of intentionally making information difficult to read, especially in computer coding. An important use case is data obfuscation, in which sensitive data is made unrecognizable to protect it from unauthorized access. Various methods are used for this.

For example, only the last four digits of a credit card number are often displayed, while the remaining digits are replaced by Xs or asterisks. In contrast, encryption involves converting data into an unreadable form that can only be decrypted using a special key.

Obfuscation In Code

When computer code is obfuscated, complex language and redundant logic are used to make the code difficult to understand. The aim? To deceive both human readers and programs such as decompilers. To do this, parts of the code are encrypted, metadata is removed, or meaningful names are replaced by meaningless ones. Inserting unused or meaningless code is also a common practice to disguise the actual code.

A so-called obfuscator can automate these processes and modify the source code so that it still works but is more difficult to understand.

Other methods of obfuscation include compressing the entire program, making the code unreadable, and changing the control flow to create unstructured, difficult-to-maintain logic.

Inserting dummy code that does not affect the logic or the program's result is also common.

Several techniques are often combined to achieve a multi-layered effect and increase security.

The Flip Side

Unfortunately, obfuscation is not only a protection, it is also a challenge. Obfuscation is not only used by legitimate software developers, but also by malicious software authors. The goal of obfuscation is to anonymize cyber attackers, reduce the risk of detection, and hide malware by changing the overall signature and fingerprint of the malicious code – even if the payload is a known threat. The signature is a hash, a unique alphanumeric representation of a malware element. Signatures are very often hashed, but they can also be another short representation of a unique code within a malware element.

Rather than trying to create a new signature by modifying the malware itself, obfuscation focuses on deployment mechanisms to fool antivirus solutions that rely on signatures. Compare this to the use of machine learning, predictive analysis, and artificial intelligence to improve defenses.

Obfuscation, or the disguising of code, can be both "good" and "bad". In the case of "bad" obfuscation, hackers combine various techniques to hide malware and create multiple layers of disguise. One of these techniques is packers. These are software packages that compress malware to hide its presence and make the original code unreadable. Then there are cryptographers who encrypt malware or parts of software to restrict access to code that could alert antivirus programs.

Another method is the insertion of dead code. This involves inserting useless code into the malware to disguise the program's appearance. Attackers can also use command modification, which involves changing the command codes in malware programs. This changes the appearance of the code, but not its behavior.

Obfuscation in the code is, as we have seen, only the first step because no matter how much work the hacker puts into obfuscating the code to bypass EDR, malware must communicate within the network and to the outside world to be "successful". This means that communication must also be obfuscated. In contrast to the past, when networks were scanned quickly, and attempts were immediately made to extract data in the terabyte range at once, attackers today communicate more quietly so that the sensors and switches for the monitoring tools do not strike.

The aim to get IP addresses via scanning, for example, is now followed more slowly to stay under the radar. Reconnaissance, in which the threat actors try to collect data about their targeted victims, e.g. via their network architecture, is also becoming slower and more obscure.

A common obfuscation method is Exclusive OR (XOR). This method hides data in such a way that it can only be read by people who link the code with 0x55 XOR. ROT13 is another trick in which letters are replaced by a code.

Blasts From The Past:

• A well-known example of obfuscation is the SolarWinds attack in 2020. Hackers used obfuscation to bypass defenses and hide their attacks.
• Another interesting example is PowerShell, a Microsoft Windows tool that attackers are abusing. Malware that uses PowerShell obscures its activities through techniques such as string encoding, command obfuscation, dynamic code execution, and more.
• Another example is the XLS.HTML attack. Here, hackers used elaborate obfuscation techniques to hide their malicious activities. They changed their encryption methods at least ten times within a year to avoid detection. Their tactics included plain text, escape encoding, Base64 encoding, and even Morse code.
• In another threat, attackers exploited vulnerabilities in ThinkPHP to execute remote code on servers. They installed a cloaked web shell called "Dama" that allowed permanent access and further attacks.

Why You Should Not Rely On Signatures Alone

Signature-based detection is like an old friend–it's reliable when it comes to known threats. But when it comes to new, unknown threats, it can sometimes be in the dark. Here are a few reasons why you shouldn't rely solely on signatures:

1. Malware authors are true masters of hide and seek. They use various techniques to disguise their malicious programs. Even small changes to the code can cause signature detection to fail.
2. With polymorphic malware, malware behaves like a chameleon. It constantly changes its structure to avoid detection. Every time it is executed, the code looks different.
3. Static signatures? Not a chance! Metamorphic malware is even more tricky. It adapts during execution and changes its code dynamically, making it almost impossible to catch with static signatures.
4. Also, zero-day exploits behave like the "new kid on the block": they are fresh and unknown, and signature-based systems have no chance of recognizing them.
5. Besides that, when a signature-based solution returns too many false positives, it becomes inefficient. Too many false alerts in daily business affect your security team and waste valuable resources.

In short, signature detection, e.g., in an EDR, is a useful tool, but it's not enough on its own to ward off all threats. A more comprehensive security strategy that also includes behavioral analysis, machine learning, and other modern techniques is essential.

Why NDR Tools Are So Important

Anomaly-based IDS solutions are like detectives who keep an eye on a system's normal behavior and sound the alarm when they detect unusual activity. But Network Detection and Response (NDR) tools even go a step further: they constantly adapt to stay one step ahead of the changing cyber threat landscape and offer a significantly higher level of security than traditional signature-based approaches through their advanced analysis and integration. They are able to detect and defend against both known and unknown threats.

Here's How They Do It:

• Behavioral Analysis: NDR tools monitor network traffic and analyze behavior. They detect unusual patterns that could indicate command-and-control (C&C) communication, such as irregular data transfers.
• Protocol Monitoring: They examine HTTP requests, DNS traffic, and other protocols to detect suspicious behavior or communication that may be associated with obfuscated malware.
• Metadata Analysis: NDR tools analyze metadata to detect unusual patterns that indicate suspicious activity. Machine learning models help identify typical obfuscation techniques that are visible through suspicious behavior in network traffic.
• Long-term Communication Monitoring: As obfuscating communication is now crucial for hackers, as they adopt slower and stealthier techniques to evade detection and collect data within and outside networks, it is helpful that NDR also looks at longer periods of time, e.g. 3 days, in addition to its ability to perform batch runs, e.g. within minutes, in order to have comparative values and monitor and detect irregularities, and real-time alerting would lead to a large number of alerts if a scan with a ping is detected every minute or so. But is every ping an attack? Certainly not!
• Mitre ATT&CK and ZEEK: These protocols provide valuable insights into threats that use obfuscation. Their integration with NDR tools significantly improves threat detection capabilities.
• Threat Data Sharing: NDR tools share threat data with other security solutions. This enables faster detection of known obfuscation techniques and suspicious behavior. The integration with EDR tools allows them to correlate suspicious activity on endpoints with network traffic, which significantly improves security analysis.

For more on why NDR is a crucial security tool and how it detects even the most advanced threats and complex forms of obfuscation, download our whitepaper on Advanced Persistent Threat (APT) detection.

To see how NDR acts in your corporate network, and precisely how it detects and responds to APTs, watch our recorded APT detection video.

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