Reynolds ransomware (first reported February 2026) embeds a malicious/vulnerable driver to disable EDR via Bring Your Own Vulnerable Driver (BYOVD), then escalates privileges and operates undetected.
Windows environments relying on EDR that can be neutralized through driver abuse.
Disabling EDR lets ransomware run without detection, enabling undetected breaches, downtime, and financial loss.
- Enable Microsoft's vulnerable-driver blocklist with WDAC and HVCI.
- Hunt for rundll32.exe loading unusual DLL/driver entry points.
- Monitor for driver loads (Sysmon EID 6) against a known-bad list.
- Maintain offline backups and segment critical systems.
Key Technical Findings
Ransomware using BYOVD to disable EDR (Reynolds).
Windows endpoints/servers permitting vulnerable driver loads.
Not specified in the source material.
Exploitation for client execution (T1203); driver loaded via rundll32.exe.
Compromised driver configured to persist through reboots.
Exploitation of driver vulnerability for elevated privileges (T1068).
Loading a vulnerable driver to disable EDR/security tooling.
Credential harvesting after escalation (Potential – requires validation).
Not specified in the source material.
Not specified in the source material.
High – undetected ransomware execution and impact.
Technical Background
Reynolds ransomware’s evasion hinges on BYOVD: it ships a vulnerable driver and loads it – reportedly via rundll32.exe invoking a malicious DLL entry point – to gain kernel-level capability and disable EDR. With defenses blinded, the operators escalate privileges and proceed toward encryption.
The technique exploits the trust the OS places in signed drivers, so the strongest controls are driver allow/block-listing, HVCI, and detection of anomalous driver loads.
Attack Chain Analysis
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Execution
ActivityLoad the vulnerable driver via rundll32.exe (T1203).
Evidencerundll32 loading unusual DLLs/drivers.
TelemetrySysmon EID 1/6, EDR.
Detection opportunityAlert on rundll32 with suspicious driver parameters.
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Privilege Escalation
ActivityAbuse driver vulnerability for elevation (T1068).
EvidenceUnexpected privilege-escalation events.
TelemetrySecurity logs, EDR.
Detection opportunityAnalyze logs for unexpected escalation.
-
Defense Evasion
ActivityDisable EDR via the driver.
EvidenceEDR tamper/stop events.
TelemetryEDR tamper alerts.
Detection opportunityAlert on security-tool tampering.
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Persistence
ActivityConfigure driver to survive reboot.
EvidenceNew boot-start driver/service.
TelemetrySystem 7045, Sysmon.
Detection opportunityHunt for new persistent drivers.
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Impact
ActivityEncrypt data (T1486).
EvidenceMass file changes and ransom notes.
TelemetryEDR/FIM.
Detection opportunityDetect rapid encryption.
Deep Technical Behavior Analysis
The high-signal behavior is rundll32.exe loading an uncommon driver DLL followed by EDR tampering. Because the driver operates at kernel level, user-mode-only monitoring may miss it – making driver-load telemetry (Sysmon EID 6) and the Microsoft blocklist essential.
Credential harvesting and exact driver hashes are Potential – requires validation and not fully specified in the source material.
Indicators of Compromise
Indicators of Behavior
Behavioral indicators to hunt for even when atomic IoCs are limited (Potential — validate against your baseline).
| Behavioral Indicator | Description | Data Source | Confidence |
|---|---|---|---|
| Anomalous PowerShell execution | Encoded/obfuscated commands, download cradles, or unusual parent-child process lineage. | Sysmon EID 1, PowerShell 4104 | Potential |
| Suspicious child process lineage | Office or web/service processes spawning script hosts or shells. | Sysmon EID 1, EDR | Potential |
| Security log clearing | Event log cleared or audit policy changed to hinder visibility. | Windows Security 1102, 4719 | Potential |
| New service / scheduled task creation | Unexpected persistence via services or tasks. | Security 7045, 4698; Sysmon | Potential |
| Web shell-like activity | New/modified server-side scripts in writable web paths; anomalous POSTs. | Web access/error logs, FIM | Potential |
| Abnormal 403/404/500 patterns | Enumeration or exploitation attempts against endpoints. | Web server logs, WAF | Potential |
| Beaconing to rare destinations | Periodic outbound connections to newly-seen domains/IPs or direct-IP C2. | Proxy, firewall, DNS logs | Potential |
| Unusual DNS queries | High-entropy or rare domains; possible tunneling. | DNS resolver logs | Potential |
Detection Engineering Guidance
Defensive detection logic (Potential — tune to your environment). No exploit code is included; logic is for hunting and alerting only.
Recommended Log Sources
| Platform | Log Source | What to Look For | Priority |
|---|---|---|---|
| Windows | Security Event Log | Logon (4624/4625), service (7045), task (4698), log clear (1102) | High |
| Windows | Sysmon | Process creation (1), network (3), image load (7), LSASS access (10) | High |
| Windows | PowerShell Operational | Script block logging (4104), module logging | High |
| Endpoint | EDR / Defender telemetry | Process tree, persistence, tamper attempts | High |
| Web | Web server access logs | Anomalous POSTs, new endpoints, web-shell-like requests | High |
| Web | Web server error logs | Repeated 403/404/500 bursts on single endpoints | Medium |
| Network | DNS resolver logs | Rare/high-entropy domains, tunneling | Medium |
| Network | Proxy / firewall logs | Beaconing, direct-IP C2, exfil volume | High |
MITRE ATT&CK Mapping
| Tactic | Technique ID | Technique Name | Relevance | Detection Opportunity | Confidence |
|---|---|---|---|---|---|
| Execution | T1203 | Exploitation for Client Execution | Utilizing vulnerabilities in client applications to execute the payload. | Monitor application logs for error messages or unusual access patterns. | Reported |
| Privilege Escalation | T1068 | Exploitation of Elevation of Privilege | Exploiting system vulnerabilities to gain elevated privileges. | Analyze logs for unexpected privilege escalation events. | Reported |
Incident Response Guidance
- Validate exposure and confirm whether the issue applies to your environment.
- Preserve evidence (memory, disk, relevant logs) before remediation.
- Isolate affected hosts/accounts if compromise is suspected.
- Collect volatile data and review the log sources listed above.
- Hunt for the indicators of behavior and any related atomic indicators.
- Rotate potentially exposed credentials, keys, and session tokens.
- Remove persistence (tasks, services, keys, web shells, cron, OAuth grants).
- Patch affected systems; reimage where integrity cannot be assured.
- Run post-remediation validation and a BAS/security-validation retest.
Remediation and Hardening
- Patch affected systems and reduce internet-exposed services.
- Enforce MFA and least-privilege for privileged and remote access.
- Improve endpoint telemetry (Sysmon/EDR) and PowerShell logging.
- Restrict script execution and constrain LOLBins where feasible.
- Monitor persistence locations and disable unnecessary services.
- Segment critical assets and review privileged accounts.
- Rotate secrets and remove credentials from configuration files.
- Tune SIEM/EDR detections, then validate controls after changes.
Business Risk
- Service disruption: degraded or unavailable systems during compromise or recovery.
- Data exposure: risk to sensitive, regulated, or customer data depending on scope.
- Regulatory exposure: potential breach-notification and compliance obligations.
- Financial impact: incident response, downtime, and potential extortion costs.
- Brand and trust impact: reputational damage with customers and partners.
- Operational continuity: ransomware can halt critical business processes until restored.
Executive Takeaway
What leadership needs to know: Disabling EDR lets ransomware run without detection, enabling undetected breaches, downtime, and financial loss. Current assessed risk: High.
Prioritise: patching/exposure reduction, identity hardening (MFA, least privilege), and detection coverage for the techniques above.
Validate after remediation: re-test controls with breach & attack simulation to confirm the relevant techniques are now prevented or detected.
Validating Your Defenses with Valitrix
A robust defense against sophisticated threats like Reynolds ransomware necessitates continuous validation of security controls. The Valitrix Breach and Attack Simulation (BAS) platform safely emulates specific ATT&CK techniques associated with ransomware attacks. By utilizing real-world adversary tactics mapped to the MITRE ATT&CK framework, organizations can verify their detection capabilities against BYOVD techniques employed by such malware.
This proactive approach allows security teams to identify gaps in their defenses before an actual attack occurs. Continuous assessments ensure that endpoint protection measures are not only in place but also effective against potential evasion tactics employed by adversaries.
Key Takeaways
- Reynolds ransomware employs BYOVD techniques to bypass EDR security tools effectively.
- A comprehensive understanding of BYOVD methodologies is critical for effective defense strategies.
- Implementing continuous monitoring and robust incident response plans can mitigate risks associated with ransomware threats.
- Regular patching and application control are essential components of a strong security posture against evolving threats.
Frequently Asked Questions
What is BYOVD?
BYOVD stands for Bring Your Own Vulnerable Driver, a technique where attackers exploit legitimate drivers with known vulnerabilities to disable security measures.
How does Reynolds ransomware operate?
This ransomware embeds a malicious driver within its payload that executes commands to disable EDR tools and evade detection mechanisms.
What can organizations do to protect against such threats?
Organizations should implement continuous monitoring, use application control, regularly patch systems, and develop comprehensive incident response plans.
