Internet Explorer — CraftedSignal Threat Feed

Potential Command and Control via Internet Explorer COM Abuse

hello@craftedsignal.io — Wed, 03 Jan 2024 18:12:00 +0000

This detection rule identifies potential command and control (C2) activity abusing Internet Explorer (iexplore.exe) via the Component Object Model (COM) on Windows systems. The technique involves launching iexplore.exe through COM, often using system binaries like rundll32.exe or regsvr32.exe to proxy the execution and evade security controls. The rule focuses on identifying unusual DNS queries originating from iexplore.exe, excluding those directed towards common Microsoft and OCSP-related domains. This tactic allows adversaries to make network connections appearing benign while hosting malicious content or performing C2 functions. The rule is designed for environments using Elastic Defend. The rule was last updated on 2026/05/04.

Attack Chain

Adversary gains initial access to the targeted system (e.g., through phishing or exploiting a vulnerability).
The adversary uses rundll32.exe or regsvr32.exe to load IEProxy.dll, which is used to instantiate Internet Explorer via COM.
Iexplore.exe is launched as a child process of rundll32.exe or regsvr32.exe with the -Embedding flag, indicating it was started via COM.
Iexplore.exe initiates DNS queries to resolve domains for command and control communication or to retrieve malicious payloads.
The DNS queries bypass typical whitelists by using uncommon or attacker-controlled domains.
Iexplore.exe establishes network connections to external IP addresses associated with the malicious domains.
Data is exfiltrated or further commands are received through the established connections.
The adversary maintains persistence and control over the compromised system.

Impact

Successful exploitation allows adversaries to establish a covert command and control channel, potentially leading to data theft, system compromise, or further propagation within the network. The use of Internet Explorer, a trusted system binary, helps evade detection and bypass host-based firewalls. The impact can range from individual workstation compromise to broader network breaches, depending on the attacker’s objectives.

Recommendation

Deploy the Sigma rule Potential Command and Control via Internet Explorer to your SIEM and tune for your environment.
Investigate any alerts generated by the Sigma rule, focusing on the parent processes (rundll32.exe, regsvr32.exe) and the destination domains of the DNS queries.
Monitor process execution events for instances of iexplore.exe being launched with the -Embedding flag, especially when the parent process is rundll32.exe or regsvr32.exe.
Review network connection logs for iexplore.exe to identify any unusual or suspicious outbound connections to domains not associated with standard Microsoft services or internal resources.
Implement network-level controls to block communication with any identified malicious domains.

Kerberos Traffic from Unusual Process

hello@craftedsignal.io — Wed, 03 Jan 2024 14:00:00 +0000

This detection identifies unusual processes initiating network connections to the standard Kerberos port (88) on Windows systems. Typically, the lsass.exe process handles Kerberos traffic on domain-joined hosts. The rule aims to detect processes other than lsass.exe communicating with the Kerberos port, which could indicate malicious activity such as Kerberoasting (T1558.003) or Pass-the-Ticket (T1550.003). The detection is designed to work with data from Elastic Defend and SentinelOne Cloud Funnel. This can help security teams identify potential credential access attempts and lateral movement within the network.

Attack Chain

An attacker compromises a user account or system within the domain.
The attacker executes a malicious binary or script (e.g., PowerShell) on the compromised system.
The malicious process attempts to request Kerberos service tickets (TGS) for various services within the domain. This is done by connecting to the Kerberos port (88) on a domain controller.
The attacker uses tools like Rubeus or Kerberoast.ps1 to enumerate and request TGS tickets.
The unusual process (not lsass.exe) sends Kerberos traffic to the domain controller.
The attacker extracts the Kerberos tickets from memory or network traffic.
The attacker cracks the offline TGS tickets to obtain service account passwords (Kerberoasting).
The attacker uses the compromised service account credentials to move laterally within the network or access sensitive data.

Impact

A successful Kerberoasting or Pass-the-Ticket attack can lead to unauthorized access to sensitive resources and lateral movement within the network. Attackers can compromise service accounts with elevated privileges, potentially leading to domain-wide compromise. Detection of this behavior can prevent attackers from gaining access to critical assets. While the exact number of victims and sectors targeted are unknown, this technique is widely used by various threat actors in targeted attacks.

Recommendation

Deploy the “Kerberos Traffic from Unusual Process” Sigma rule to your SIEM and tune for your environment. Enable network connection logging to capture the necessary traffic.
Investigate any alerts triggered by the Sigma rule, focusing on the process execution chain and potential malicious binaries.
Review event ID 4769 for suspicious ticket requests as mentioned in the rule’s documentation.
Examine host services for suspicious entries as outlined in the original Elastic detection rule using Osquery.
Monitor for processes connecting to port 88, filtering out legitimate Kerberos clients like lsass.exe, using the “Detect Kerberos Traffic from Non-Standard Process” Sigma rule.
Investigate processes identified by the rule and compare them to the list of legitimate processes to identify unauthorized connections to the Kerberos port.