How Qilin Uses BYOVD and Linux Payloads to Escape Detection

Qilin’s operators continually refine their toolkit. Recently, the group paired a native Linux payload with Bring-Your-Own-Vulnerable-Driver (BYOVD) techniques to evade endpoint defenses and deliver a hybrid ransomware load. Consequently, defenders face a cleaner, stealthier attack path that runs beneath traditional Windows detection layers and complicates containment. This briefing unpacks the attack chain, explains why current controls often miss it, and outlines high-confidence mitigations.

How the Hybrid Attack Works

First, attackers gain initial access through stolen credentials, exposed RDP/RMM tools, or phishing that yields privileged accounts. Next, they install a signed but vulnerable kernel driver or reuse an existing one (BYOVD), then load a small bootstrap that drops and executes a Linux binary inside a Windows environment either in a WSL context, a custom userspace loop, or via direct Linux runtime invocation. Because the driver runs at kernel level, the actor elevates privileges, suppresses security telemetry, and facilitates in-memory payload execution. Finally, the ransomware component enumerates high-value shares and virtual machines, encrypts files, and exfiltrates data for double extortion. Multiple security vendors have documented these patterns and flagged the cross-platform nature as particularly concerning. 

Why BYOVD Works Against EDR

BYOVD exploits rely on legitimate driver signing and kernel privileges. Attackers select drivers with known vulnerabilities often from older vendor packages or niche hardware utilities then load them to bypass kernel enforcement. Thus, security tools that rely on userland telemetry or signature-based detection miss kernel-level manipulation. Furthermore, because the drivers often carry valid Microsoft signatures, automated whitelisting does not always block them. Consequently, BYOVD becomes an effective stealth move for delivering complex payloads such as Linux ransomware. 

Initial Access and Post-Compromise Techniques

Qilin affiliates use a predictable but effective playbook: harvest credentials from leaks or brute force, move laterally using legal admin tooling (RMM, AnyDesk, ScreenConnect), and embed persistence via scheduled tasks or registry run keys. Simultaneously, they stage vulnerable drivers and lightweight loaders to evade detection. Once they hold domain privileges, they disable backups, stop security agents, and wipe logs before the final encryption impulse. Security researchers and vendors have observed these TTPs repeatedly in Qilin incidents.

Detection Challenges and Indicators

Detecting BYOVD-assisted attacks requires kernel and telemetry coverage. Look for these indicators:
• Unexpected driver loads of known vulnerable module names or drivers with anomalous load timestamps.
• In-memory execution of non-native binaries (Linux ELF signatures) or atypical use of WSL/containers on Windows hosts.
• Sudden termination of backup and EDR processes followed by mass file access patterns.
Because attackers attempt to suppress logs, defenders must combine kernel monitoring, file system activity analytics, and network-level egress detection to spot the pattern early. Vendor reports and SOC case studies provide sample indicators and Yara signatures for immediate use. 

Immediate Mitigation Steps

First, isolate affected hosts and revoke compromised credentials. Second, block known vulnerable driver identifiers at the kernel policy level and enforce secure driver signing and whitelisting policies. Third, implement endpoint detection that inspects kernel module loads and flags drivers loaded from atypical paths. Fourth, maintain immutable and offline backups for both file systems and VM disks. Finally, exercise incident response plans with scenarios that emulate BYOVD load

Longer-Term Hardening

Over time, organisations should adopt least-privilege for administrative tooling, reduce reliance on broad RMM privileges, and centralise driver inventory management. Also, apply tactical controls such as Application Control (allowlisting), kernel integrity validation, and strict code-signing policies. For virtualised environments, isolate management networks and enforce multifactor authentication for hypervisor admin consoles. Because Qilin affiliates adapt quickly, defenders must test and iterate controls routinely.

Recovery Considerations

When an attacker uses BYOVD and a Linux payload, recovery steps can require cross-platform coordination. First, ensure forensic capture of kernel images and memory before reboots when possible. Next, validate backups for VM consistency and run integrity checks before restoring. Finally, conduct root cause analysis focusing on the driver provenance and lateral movement path to close the exploited gaps. Incident responders should collaborate with vendor partners to analyze drivers and develop signatures for future detection. 

FAQs

Q1: What exactly is BYOVD?
A1: BYOVD stands for Bring-Your-Own-Vulnerable-Driver. Attackers load legitimate but vulnerable kernel drivers to execute privileged code and bypass endpoint protections.

Q2: Can Linux ransomware actually run on Windows?
A2: Yes. Attackers run Linux payloads on Windows hosts via WSL, embedded runtimes, or by leveraging kernel drivers that give them a path to execute non-native code.

Q3: Are signed drivers always safe?
A3: No. A valid signature proves origin, not security. Signed drivers can contain vulnerabilities; therefore, enterprises must verify driver provenance and track CVEs.

Q4: How quickly should teams act after detection?
A4: Teams should isolate affected hosts immediately, revoke credentials, and preserve forensic data. Rapid containment reduces the blast radius and prevents VM encryption escalation.

Q5: What detection controls provide the best yield?
A5: Kernel-level telemetry, driver load monitoring, immutable offline backups, and network egress analytics together provide high fidelity for BYOVD-style attacks.