Reynolds Ransomware: Kernel-Level Evasion via Embedded BYOVD for EDR Disablement

Reynolds Ransomware: Kernel-Level Evasion via Embedded BYOVD for EDR Disablement

Cybersecurity researchers have recently unveiled details of an emergent ransomware family, dubbed Reynolds, which marks a significant escalation in adversarial defense evasion techniques. What sets Reynolds apart is its ingenious integration of a Bring Your Own Vulnerable Driver (BYOVD) component directly within its ransomware payload. This sophisticated approach allows Reynolds to achieve kernel-level privileges, effectively disabling Endpoint Detection and Response (EDR) security tools and facilitating its destructive operations with unparalleled stealth and persistence.

Understanding Bring Your Own Vulnerable Driver (BYOVD) Attacks

BYOVD is an advanced adversarial technique that exploits legitimate, signed, but flawed kernel-mode drivers to gain elevated privileges. These drivers, often associated with hardware devices, virtualization software, or even outdated security tools, possess vulnerabilities that can be leveraged to execute arbitrary code in kernel space (Ring 0). Unlike user-mode attacks, operations performed in kernel mode are typically invisible or untraceable by most EDR solutions, which primarily operate at user-mode or rely on kernel-mode callbacks that can be tampered with.

The core of a BYOVD attack lies in abusing specific driver functionalities, such as:

• Arbitrary Read/Write Primitives: Exploiting IOCTLs (I/O Control Codes) that allow an attacker to read from or write to arbitrary physical or virtual memory addresses in the kernel.
• Direct Kernel Memory Manipulation: Bypassing memory protection mechanisms to modify critical kernel structures.
• Privilege Escalation: Leveraging the driver to elevate a low-privilege process to SYSTEM or even kernel-level execution context.

Once a vulnerable driver is loaded and exploited, the attacker gains an almost omnipotent control over the operating system, enabling them to bypass security controls that rely on user-mode hooks or even many kernel-mode monitoring mechanisms.

The Reynolds Ransomware Attack Chain

The attack chain for Reynolds ransomware, leveraging its embedded BYOVD, is particularly insidious:

1. Initial Access: Reynolds likely gains initial access through common vectors such as spear-phishing campaigns, exploitation of public-facing applications (e.g., RDP, VPN vulnerabilities), or supply chain compromise.
2. Payload Delivery & Dropper: Once inside, the Reynolds executable is deployed. This dropper component contains the ransomware payload itself and the embedded legitimate, but vulnerable, driver.
3. Driver Loading & Exploitation: The ransomware registers and loads the vulnerable driver. Subsequently, it interacts with this driver using specific IOCTLs or other exposed interfaces to trigger the vulnerability. This typically involves passing carefully crafted input to achieve arbitrary kernel memory read/write capabilities.
4. Kernel-Level EDR Disablement: This is the critical phase. With kernel-level arbitrary read/write access, Reynolds can perform several actions to neutralize security tools:
   • Terminating EDR Processes: Directly locating and terminating EDR processes from kernel mode, bypassing user-mode protections.
   • Modifying Kernel Callbacks: Unregistering or hooking critical kernel callbacks used by EDRs for monitoring file system activity (IRP_MJ_CREATE), process creation (PsSetCreateProcessNotifyRoutine), image loading (PsSetLoadImageNotifyRoutine), or registry access (CmRegisterCallback).
   • Unpatching & Unhooking: Reverting in-memory patches or API hooks injected by EDRs into system libraries (e.g., ntdll.dll, kernel32.dll) to regain control over system functions.
   • Disabling ETW Providers: Manipulating Event Tracing for Windows (ETW) providers used by security tools for telemetry collection.
   • Manipulating MiniFilter Drivers: If an EDR uses a MiniFilter driver for file system monitoring, Reynolds could potentially unload or tamper with its functionality.
5. Ransomware Execution: After successfully disabling security defenses, Reynolds proceeds with its primary objective: encrypting files, dropping ransom notes, and deleting shadow copies to prevent easy recovery.

Technical Deep Dive: Driver Exploitation Mechanics

The process of converting an arbitrary read/write primitive into full kernel execution is a nuanced art. Threat actors often employ techniques such as:

• Token Impersonation: Locating the _EPROCESS structure of a target process (e.g., a SYSTEM process) and copying its token to the ransomware's own process, thereby elevating its privileges.
• Code Injection: Allocating executable memory in kernel space and injecting shellcode, then using the driver's write primitive to overwrite a function pointer or a system call table entry to execute this shellcode.
• Direct Kernel Object Manipulation (DKOM): Modifying kernel data structures to hide processes, elevate privileges, or tamper with security descriptors.

The ability to interact directly with core Windows kernel components like ntoskrnl.exe and its exported functions grants Reynolds an unparalleled advantage, making detection and intervention exceedingly difficult for conventional security mechanisms.

Impact and Implications for Enterprise Security

The emergence of Reynolds ransomware with its embedded BYOVD component signals a worrying trend in the threat landscape. It represents a significant challenge for enterprise security, as it:

• Bypasses Advanced EDR/XDR: Directly undermines the core monitoring capabilities of even sophisticated EDR/XDR solutions.
• Increases Dwell Time: Undetected defense evasion allows for extended dwell time, facilitating lateral movement and broader compromise before encryption.
• Complicates Incident Response: Forensic analysis becomes more challenging due to the lack of EDR telemetry and the stealthy nature of kernel-mode operations.
• Raises Supply Chain Concerns: Highlights the risk posed by legitimate, signed drivers from third-party vendors, which can become attack vectors.

Defensive Strategies and Mitigation

Countering threats like Reynolds requires a multi-layered, proactive defense strategy:

• Strong Application Control & Driver Whitelisting: Implement strict policies like Windows Defender Application Control (WDAC) or Hypervisor-Protected Code Integrity (HVCI) to restrict which drivers can be loaded, preventing the loading of known vulnerable drivers.
• Regular Patching & Updates: Keep operating systems, applications, and especially third-party drivers up-to-date to patch known vulnerabilities.
• Principle of Least Privilege: Limit user privileges to reduce the attack surface for initial compromise and subsequent privilege escalation.
• Advanced EDR/XDR with Kernel-Level Visibility: Deploy security solutions that offer deeper kernel-level visibility and can detect anomalies in driver loading, unusual kernel memory access patterns, or attempts to tamper with kernel callbacks.
• Memory Integrity & Virtualization-Based Security (VBS): Enable VBS features like HVCI to protect kernel processes and drivers from tampering.
• Threat Hunting: Actively hunt for suspicious driver activity, unsigned drivers, unexpected kernel module loads, or unusual process behavior indicative of BYOVD exploitation.
• Network Segmentation & Offline Backups: Essential for limiting lateral movement and ensuring business continuity in case of successful compromise.

Digital Forensics, Threat Attribution, and Link Analysis

In the aftermath of a sophisticated attack like Reynolds, robust digital forensics and threat attribution are paramount. Investigators must collect and analyze every piece of available telemetry to reconstruct the attack chain, identify initial access vectors, and understand the adversary's tactics, techniques, and procedures (TTPs).

For advanced telemetry collection during incident response or threat intelligence gathering, tools like iplogger.org can be instrumental. It facilitates the collection of critical data points such as IP addresses, User-Agent strings, ISP details, and device fingerprints, enabling investigators to map attack infrastructure, understand adversary profiles, and trace the initial stages of compromise with greater precision. This metadata extraction from network communications, combined with endpoint forensics, is crucial for developing robust threat intelligence and improving defensive posture.

Conclusion

Reynolds ransomware, with its embedded BYOVD component, represents a formidable evolution in ransomware capabilities, pushing the boundaries of defense evasion into the kernel. It underscores the critical need for organizations to adopt a holistic security posture that extends beyond traditional endpoint protection, embracing advanced driver control, memory integrity, and proactive threat hunting. As adversaries continue to innovate, a layered defense strategy, informed by deep technical understanding and continuous threat intelligence, remains the strongest bulwark against such advanced persistent threats.