TL;DR: The Silent Skimmer has returned, exploiting overlooked vulnerabilities in Telerik UI to infiltrate payment systems and siphon sensitive data with alarming stealth. Leveraging CVE-2017-11317 and CVE-2019-18935, this cyber threat actor gains entry to systems, establishes persistence through reverse shells, and exfiltrates payment information using cleverly concealed Python scripts. This campaign exposes the costly risks of neglected patching and outdated security practices. Organizations relying on payment infrastructure must act now—implement regular patching, real-time monitoring, and robust endpoint defenses to avoid becoming the Silent Skimmer’s next victim.
A Sleeping Threat Awakens: How Silent Skimmer Exploits Neglected Software Flaws to Target Payment Systems
Cyber threats don’t simply disappear—they lie in wait, evolving, and striking when we least expect it. This is precisely the case with Silent Skimmer, a cyber threat actor that has resurfaced with frightening new tactics, targeting payment systems to siphon sensitive data from organizations. In May 2024, Silent Skimmer reawakened, exploiting neglected vulnerabilities in Telerik UI to breach enterprise systems, highlighting the critical dangers of unpatched software in today’s digital landscape.
Drawing on in-depth research by Unit 42 at Palo Alto Networks, we uncover how Silent Skimmer employs vulnerabilities like CVE-2017-11317 and CVE-2019-18935 to infiltrate systems, maintain a stealthy presence, and execute targeted data extractions. This sophisticated campaign is a stark reminder of how costly overlooked flaws can be for enterprises. In this analysis, we’ll delve into Silent Skimmer’s tactics, its advanced evasion techniques, and the urgent lessons organizations must take to protect themselves from this evolving menace.
Table of Contents
The Silent Skimmer Playbook: Leveraging Telerik UI Vulnerabilities
1. The Gateway Exploits: CVE-2017-11317 and CVE-2019-18935
Silent Skimmer’s most formidable asset is its ability to exploit two specific vulnerabilities within the Telerik UI framework, which is commonly used for ASP.NET applications. Both vulnerabilities are over five years old, yet they remain highly effective as entry points in Silent Skimmer’s attacks:
- CVE-2017-11317: This vulnerability allows for unrestricted file uploads, essentially enabling attackers to inject files directly into a system due to weak encryption.
- CVE-2019-18935: Through insecure deserialization, this vulnerability provides attackers with a pathway for remote code execution (RCE), granting them control over compromised systems.
The choice of Telerik UI as an entry point isn’t accidental. Despite public documentation and patches, many organizations fail to update or secure this widely used tool, leaving a lingering vulnerability that cybercriminals like Silent Skimmer are all too willing to exploit.
2. Establishing Persistence: Reverse Shells and Web Shells
Once they’ve gained initial access, Silent Skimmer uses a series of backdoors to establish long-term presence. These include:
- Web Shells: Hidden within directories such as
C:WebRootIISWeb Applications**ImagesCommon, these web shells allow attackers to execute commands remotely on compromised servers. - Reverse Shells and PowerShell Commands: Using reverse shells, the attackers utilize PowerShell scripts and
mshta.exe—a legitimate Microsoft utility—to bypass detection and maintain a secure connection to their command-and-control (C2) servers.
With these tactics, Silent Skimmer demonstrates a sophisticated understanding of “living off the land” attacks, in which common system utilities are repurposed to avoid detection.
3. The GodPotato Privilege Escalation Tool
Silent Skimmer also employs GodPotato, a tool for escalating privileges within a Windows environment. By embedding native C++ code within .NET binaries (a technique called mixed-mode assemblies), Silent Skimmer effectively hides its activities from .NET analysis tools, making it challenging for defenders to detect malicious payloads.
This tactic emphasizes how Silent Skimmer combines old and new methods: an established vulnerability exploited through innovative techniques that bypass traditional defense mechanisms. The use of mixed-mode assemblies, while not a new concept, demonstrates that Silent Skimmer is evolving by employing tactics that are difficult for standard analysis tools to recognize.
The Data Extraction Process: Compiling Python to Steal Payment Information
Once Silent Skimmer has established a foothold and gained elevated privileges within a compromised system, it turns its focus to the primary objective—extracting payment information. At this stage, the campaign deploys a carefully crafted Python script to systematically retrieve and exfiltrate sensitive financial data, using methods that add layers of obfuscation and minimize detection risks.
Python Scripting for Data Exfiltration
Silent Skimmer’s Python script connects directly to payment databases, typically using hard-coded credentials that allow quick, unauthorized access. This approach operates “invisibly” within the existing payment infrastructure, bypassing the need for injecting code into visible webpages or forms. Here’s how this stealthy data extraction process unfolds:
1. Database Connection and Query Execution
- Using the
pyodbclibrary, the script authenticates with the targeted database, leveraging hard-coded database credentials. - Once connected, the script executes SQL queries to retrieve specific fields containing payment information, such as credit card numbers, transaction IDs, and user data.
- Example Query:
SELECT card_number, expiration_date, user_id FROM transactions;
2. Data Extraction and Formatting
- Extracted data is written to a
.csvfile, making it easy for attackers to collect in a structured format. This file is often named inconspicuously (e.g.,syslog.csv) to blend with legitimate system logs. - The file output ensures that large volumes of payment data are organized and primed for efficient exfiltration.
3. Obfuscation Through Compilation
- Silent Skimmer’s script is compiled into an executable using tools like PyInstaller, which bundles the Python code into a single, self-contained executable. This method adds obfuscation, as the resulting executable is packed with extraneous data that can complicate reverse engineering.
- The compiled executable often contains unnecessary binary data and dependencies, making it harder for defenders to analyze without specific unpacking tools.
RingQ Loader: A Tool for Concealing Payloads
To load and execute malicious payloads without detection, Silent Skimmer deploys the RingQ Loader, a powerful post-exploitation tool designed for both stealth and adaptability. This loader serves two critical functions:
1. Loading Encrypted Payloads
The RingQ Loader is configured to load encrypted payloads, which can be stored locally on the compromised system or fetched remotely. This encrypted format prevents traditional security tools from flagging the payload as malicious until it’s decrypted and executed.
2. Mimicking Legitimate Applications
The loader frequently masquerades as widely trusted applications like PuTTY, a known SSH client, by replicating its appearance and metadata. This allows it to evade detection by endpoint security tools that might otherwise scrutinize unknown binaries.
Downloader Functionality
When configured, the RingQ Loader can act as a downloader, retrieving additional malicious components or updated versions of malware from external servers. By fetching payloads in real-time, the loader remains dynamic, adapting to changing attack requirements or security measures in the environment.
Technical Note: Stealth and Execution Flow
RingQ employs a process called “reflective loading” that allows it to execute in-memory without needing to write code to disk. This reduces its footprint and can bypass anti-malware software that relies on disk-scanning mechanisms. After decrypting the payload, the loader initiates the execution of commands that access and exfiltrate the prepared .csv file, sending it to command-and-control (C2) servers.
Silent Skimmer’s use of Python scripting, combined with tools like RingQ Loader, enables attackers to extract sensitive payment data with minimal detection. This approach leverages stealth techniques—direct database access, obfuscated Python executables, and payload encryption—illustrating the evolving sophistication in modern data exfiltration campaigns.
Lessons from the Silent Skimmer: Closing the Security Gaps
The reemergence of the Silent Skimmer campaign underscores key areas where organizations often fall short in cybersecurity, leaving them vulnerable to attacks. By examining these vulnerabilities and implementing targeted improvements, companies can bolster their defenses against similar advanced threats. Here are the main takeaways from this campaign and actionable steps for mitigating risk.
1. Patch Management: The Foundation of Cyber Defense
Unpatched software remains one of the most significant security gaps in enterprises. The Silent Skimmer exploits vulnerabilities in outdated software, such as CVE-2017-11317 and CVE-2019-18935 in the Telerik UI. These vulnerabilities were disclosed years ago and have had patches available, yet many organizations are still at risk due to lapses in patch management.
- Automated Patch Management: Implement automated tools to keep software updated across all endpoints. Tools like Qualys Patch Management and ManageEngine Patch Manager Plus automate patch deployment, helping reduce human error and time delays.
- Vulnerability Scanning and Prioritization: Conduct regular vulnerability assessments using tools like Nessus or Rapid7 Nexpose. Prioritize critical vulnerabilities with high Common Vulnerability Scoring System (CVSS) scores, particularly those known to be exploited in the wild, as indicated in the CISA Known Exploited Vulnerabilities Catalog.
Example: In a 2023 report by Ponemon Institute, 60% of data breaches involved vulnerabilities that had known patches, highlighting the importance of proactive patch management.
2. Endpoint Monitoring and Response: Proactive Detection
Silent Skimmer leverages tools and utilities already present on systems, like mshta.exe, to evade detection through “living off the land” techniques. This makes robust Endpoint Detection and Response (EDR) crucial for spotting and isolating unusual activity.
- Behavioral Analysis with EDR: Solutions like CrowdStrike Falcon and Cortex XDR use behavioral analysis to identify irregular activity on endpoints, such as unauthorized file access, unusual directory traversal, or unexpected process launches.
- Incident Response Playbooks: Equip your security team with clear incident response protocols for dealing with potentially malicious activity detected by EDR tools. Regularly train teams on response playbooks to ensure swift action in isolating threats.
Example: CrowdStrike’s 2023 Threat Report found that 68% of intrusions utilized legitimate tools within the system, emphasizing the need for behavioral monitoring over signature-based detection.
3. Network Security Audits: Identifying Configuration Weaknesses
Regularly auditing network configurations helps identify weak points that attackers could exploit for persistent access. Misconfigured firewalls and open ports provide Silent Skimmer and similar actors with entry points and make lateral movement within the network easier.
- Firewall Configuration: Enforce strict firewall rules to limit traffic only to necessary resources, segmenting the network to protect sensitive data and systems.
- Port and Service Monitoring: Routinely scan open ports using tools like Nmap to ensure only essential ports are accessible. Use network segmentation and access control lists (ACLs) to restrict sensitive data from vulnerable segments.
Example: In the 2022 IBM Cost of a Data Breach Report, misconfigured firewalls were a significant contributor to data breaches, costing companies an average of $4.24 million per incident.
4. User Education: Strengthening the Human Layer
Although Silent Skimmer primarily targets software vulnerabilities, improving user awareness about remote code execution (RCE) and other attack vectors can reduce the risk of additional vulnerabilities being introduced through user error.
- Cyber Hygiene Training: Train employees on cyber hygiene principles, such as verifying the authenticity of software sources and recognizing suspicious activity.
- Periodic Security Drills: Conduct simulated security incidents to educate employees on best practices. This could include identifying potentially malicious links or understanding unusual software requests.
Example: According to a Verizon Data Breach Investigations Report, 85% of breaches involve human error, underscoring the importance of regular user education on cybersecurity fundamentals.
The Silent Skimmer campaign highlights that closing common security gaps, such as patching software, monitoring endpoints, performing network audits, and educating users, is essential to prevent advanced cyber threats. By reinforcing these foundational elements, organizations can significantly reduce the likelihood of exploitation and data breaches.
FAQs
What is the primary vulnerability exploited by the Silent Skimmer campaign?
Silent Skimmer primarily exploits outdated vulnerabilities in Telerik UI, specifically CVE-2017-11317 and CVE-2019-18935. These vulnerabilities allow attackers to perform unrestricted file uploads and remote code execution, giving them initial access to systems running unpatched versions of Telerik UI in ASP.NET applications. These flaws, although patchable, are still widely unaddressed, making them a significant entry point for the campaign.
How does the Silent Skimmer evade detection during data extraction?
Silent Skimmer evades detection by using “living off the land” techniques, which involve using legitimate system utilities (like mshta.exe and PowerShell) to carry out malicious actions. For data extraction, it employs compiled Python scripts and obfuscation tactics, such as bundling unnecessary binary data into executables using tools like PyInstaller. Additionally, by using RingQ Loader, it conceals and encrypts its payloads, making it harder for traditional endpoint detection systems to identify malicious actions.
What is RingQ Loader, and why is it effective in cyber attacks?
RingQ Loader is a post-exploitation tool used to load and execute encrypted payloads within a compromised system. It’s effective in cyber attacks because it often masquerades as legitimate software, like PuTTY, to avoid detection. By running in-memory and not writing code directly to disk, RingQ Loader further evades traditional file-based detection methods. Additionally, its downloader functionality allows it to dynamically fetch other malware components, making it adaptable to different stages of the attack.
Why is regular patch management crucial for preventing attacks like Silent Skimmer?
Regular patch management is essential because vulnerabilities in commonly used software are often targeted by attackers. In Silent Skimmer’s case, vulnerabilities like CVE-2017-11317 and CVE-2019-18935 in Telerik UI have been known for years, yet they remain unpatched in many environments. Without timely updates, these vulnerabilities act as open doors for attackers, allowing initial access to systems. Automated patching and vulnerability assessments are critical for closing these entry points and reducing the risk of exploitation.
How does endpoint monitoring help in detecting Silent Skimmer attacks?
Endpoint monitoring, particularly through advanced Endpoint Detection and Response (EDR) systems, helps in identifying unusual activities indicative of an attack. Silent Skimmer often uses system utilities, like mshta.exe, in unexpected ways or accesses unusual directories to execute its payloads. EDR tools analyze these behaviors in real-time and alert security teams to suspicious patterns, such as unauthorized file access or irregular process activity, which are crucial for early detection and mitigation of such sophisticated attacks.
What steps can organizations take to secure their networks against similar threats?
Organizations can secure their networks by implementing a layered security approach, which includes regular network security audits, segmentation, and strict firewall configurations. Network audits help identify misconfigured elements, such as open ports or firewall rules, that could expose systems to external threats. Segmenting networks limits lateral movement, restricting attackers’ access to sensitive resources even if they breach one area. Properly configured firewalls also help control traffic flow, preventing unauthorized connections that could facilitate data exfiltration.
Why is cybersecurity training for employees important even if the primary attack is not phishing?
Cybersecurity training for employees is crucial because it educates users on recognizing suspicious behavior that could otherwise aid attackers. For example, in the case of Silent Skimmer, employees familiar with cyber hygiene are less likely to install unauthorized software or engage in activities that could open further vulnerabilities. Training helps foster a culture of vigilance, reducing the risk of additional entry points and increasing the overall security resilience of the organization.
Conclusion: Staying Ahead of the Silent Skimmers
The Silent Skimmer is a formidable reminder that “silent” threats are often the most dangerous. Leveraging neglected vulnerabilities and sophisticated obfuscation techniques, it has managed to remain a persistent, evolving threat to payment infrastructures. As organizations move forward, adopting a proactive security posture, including real-time threat monitoring and continuous updates, can be the difference between evading or falling victim to campaigns like the Silent Skimmer.
If your organization manages payment data or hosts infrastructure vulnerable to exploitation, now is the time to evaluate your security policies, patch systems, and strengthen detection capabilities. Cyber threats may be relentless, but with the right defenses, you can ensure they never gain a foothold.
