Detection of Bcdedit Boot Configuration Modification

This detection rule identifies the execution of bcdedit.exe with specific arguments that modify the boot configuration data (BCD) store in Windows systems. Attackers or malware may use this technique to disable Windows Error Recovery (recoveryenabled) or to ignore errors during the boot process (bootstatuspolicy ignoreallfailures). These modifications are often performed to prevent systems from recovering properly after an attack, particularly in ransomware scenarios. The rule is designed to work with data from Elastic Defend, CrowdStrike, Microsoft Defender XDR, SentinelOne Cloud Funnel, and Sysmon. The detection logic focuses on process execution events that include the relevant bcdedit.exe command-line arguments. Defenders should be aware of legitimate uses of bcdedit.exe by administrators for troubleshooting or data recovery purposes, so context is crucial.

Attack Chain

1. Initial Access: The attacker gains initial access to the system through various means, such as phishing or exploiting a vulnerability.
2. Privilege Escalation: The attacker escalates privileges to gain administrative access, required to modify boot configuration settings.
3. Reconnaissance: The attacker performs reconnaissance to identify the system’s configuration and identify appropriate targets for modification.
4. Disable Recovery: The attacker uses bcdedit.exe to disable Windows Error Recovery using the /set {default} recoveryenabled No command.
5. Ignore Boot Failures: The attacker uses bcdedit.exe to set the boot status policy to ignore all failures using the /set {default} bootstatuspolicy ignoreallfailures command.
6. System Impact: By modifying the boot configuration, the attacker inhibits system recovery, making it harder for the system to recover from errors or malicious activity.
7. Payload Execution: The attacker deploys and executes the primary malicious payload, such as ransomware, leveraging the modified boot configuration to maximize impact.
8. Final Objective: The attacker achieves their final objective, which could include data encryption, data theft, or system disruption.

Impact

Successful modification of boot configuration data can lead to significant system instability and data loss. In ransomware attacks, this technique prevents the system from recovering, increasing the likelihood of the victim paying the ransom. While the exact number of affected organizations is unknown, this technique is widely used in ransomware campaigns and can affect any Windows system if successfully executed.

Recommendation

• Deploy the “Modification of Boot Configuration” Sigma rule to your SIEM and tune for your environment to detect the malicious use of bcdedit.exe described in this brief.
• Enable Sysmon process creation logging to capture bcdedit.exe executions and their command-line arguments (Sysmon Event ID 1).
• Investigate any detected instances of bcdedit.exe modifying boot configuration settings to determine legitimacy, as described in the rule’s “Triage and analysis” section.
• Monitor process execution logs for unexpected processes running bcdedit.exe with arguments related to disabling recovery or ignoring boot failures.