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Everything you need to know about CryptoLocker ransomware

In this magazine post, we will explore the CryptoLocker ransomware and examine it’s impact in the world of Cybersecurity. Prior to beginning, ensure you subscribe to Cyber Puffin to remain informed about developments in the field of cybersecurity.

Everything you need to know about CryptoLocker ransomware

In the ever-evolving landscape of cybersecurity threats, one name strikes fear into the hearts of both individuals and organizations alike: CryptoLocker ransomware. This malicious software doesn’t just sneak into your digital life; it hijacks your files and holds them hostage until a ransom is paid. But what exactly is CryptoLocker, and why is it such a formidable foe in the realm of cybersecurity?


What is CryptoLocker ransomware?

CryptoLocker has gained widespread notoriety as a malicious software capable of inflicting significant harm on data-centric enterprises. Upon execution, it encrypts files stored on both individual desktops and network shares, effectively holding them hostage until a ransom is paid for decryption. For this reason, CryptoLocker and its variants have come to be known as “ransomware.”

What is CryptoLocker ransomware?

Malicious software such as CryptoLocker can find its way into a secured network through various avenues like email, file sharing platforms, and downloads. Recent versions have managed to evade traditional antivirus and firewall defenses, and it’s likely that more will arise capable of circumventing preventive measures. Besides restricting the potential damage a compromised system can cause by reinforcing access controls, it’s advisable to implement detective and corrective measures as an additional layer of defense.


How can CryptoLocker ransomware harm you?

Upon execution, CryptoLocker initiates a scan on mapped network drives that the host is linked to, searching for folders and documents, and proceeds to rename and encrypt those accessible for modification based on the permissions granted to the user executing the code.

Using an RSA 2048-bit key, CryptoLocker encrypts the files and appends an extension to their names, such as .encrypted, .cryptolocker, or .[7 random characters], depending on the variant. Subsequently, the malware generates a file within each affected directory, directing users to a webpage with decryption instructions that necessitate a payment (e.g., via bitcoin). These instruction files typically bear names like DECRYPT_INSTRUCTION.txt or DECRYPT_INSTRUCTIONS.html.

As new variants emerge, updates will be provided on the Varonis Connect discussion regarding Ransomware. For instance, a variant dubbed “CTB-Locker” generates a singular file in the directory where it initiates file encryption, named !Decrypt-All-Files-[RANDOM 7 chars].TXT or !Decrypt-All-Files-[RANDOM 7 chars].BMP.


How to protect yourself from CryptoLocker ransomware?

The extent of damage that malware can cause is directly related to the number of files accessible by a user account. Therefore, it’s wise to limit access, which in turn reduces the potential for encryption of sensitive data. Apart from providing a defense against malware, this approach also minimizes the risk of exposure to various other internal and external threats.

Transitioning to a least privilege model may not offer an immediate solution, but it’s possible to swiftly reduce exposure by removing unnecessary global access groups from access control lists. Groups like “Everyone,” “Authenticated Users,” and “Domain Users,” when applied to data containers such as folders and SharePoint sites, can expose entire hierarchies to all users within a company. These exposed datasets not only become easy targets for theft or misuse but are also highly susceptible to damage in the event of a malware attack. On file servers, such folders are often referred to as “open shares” when both file system and sharing permissions are accessible via a global access group.

While utilizing technologies tailored to identifying and removing global access groups is the simplest approach, it’s also feasible to detect open shares by creating a user account devoid of group memberships. This account’s credentials can then be employed to “scan” the file sharing environment.


How to detect CryptoLocker ransomware?

When monitoring file access activity on impacted file servers, these actions can lead to a significant increase in open, modify, and create events at a rapid rate. Fortunately, such patterns are relatively easy to identify through automation, offering a valuable detective control. For instance, if a single user account alters 100 files within a minute, it’s likely indicative of automated activity. Ensure your monitoring system is configured to generate alerts upon detecting such behavior.

If you lack an automated system to track file access activity, you might find yourself needing to resort to enabling native auditing. However, native auditing can strain monitored systems and the resulting logs can be challenging to interpret. Instead of attempting to activate and gather native audit logs for every system, focus on the most sensitive areas and contemplate establishing a file share honeypot.


A file share honeypot is essentially a bait—a file share that appears to contain regular or valuable files but is actually filled with decoys. Since no genuine user activity should be occurring within a honeypot file share, any detected activity must be thoroughly examined. If you’re relying on manual methods, you’ll have to activate native auditing to track access activity and develop a script to notify you when events are logged in the security event log.

How to detect CryptoLocker ransomware?

When your detective control system is capable of initiating an automated response, like disabling the user account, it effectively halts the attack before it can cause additional harm.

In summary, the dangers presented by CryptoLocker ransomware are significant and far-reaching. Its ability to enter networks through various means, evade conventional security measures, and encrypt essential files makes it a serious threat to both individuals and organizations. The financial burden of ransom payments, along with the potential loss of critical data and disruptions to operations, highlight the urgent need for strong cybersecurity practices. As ransomware attacks continue to evolve, it’s crucial for individuals and businesses to stay vigilant, strengthen their defenses, and take proactive steps to mitigate the risks posed by CryptoLocker and similar malicious software.


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