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Original release date: August 14, 2020
This Alert uses the MITRE Adversarial Tactics, Techniques, and Common Knowledge (ATT&CK®) framework. See the ATT&CK for Enterprise framework for all referenced threat actor techniques.
The Cybersecurity and Infrastructure Security Agency (CISA) has observed cyber actors using emails containing a Microsoft Word document with a malicious Visual Basic Application (VBA) macro code to deploy KONNI malware. KONNI is a remote administration tool (RAT) used by malicious cyber actors to steal files, capture keystrokes, take screenshots, and execute arbitrary code on infected hosts.
KONNI malware is often delivered via phishing emails as a Microsoft Word document with a malicious VBA macro code (Phishing: Spearphising Attachment [T1566.001]). The malicious code can change the font color from light grey to black (to fool the user to enable content), check if the Windows operating system is a 32-bit or 64-bit version, and construct and execute the command line to download additional files (Command and Scripting Interpreter: Windows Command Shell [T1059.003]).
Once the VBA macro constructs the command line, it uses the certificate database tool CertUtil to download remote files from a given Uniform Resource Locator. It also incorporates a built-in function to decode base64-encoded files. The Command Prompt silently copies
The cyber actor then downloads a text file from a remote resource containing a base64-encoded string that is decoded by CertUtil and saved as a batch (.BAT) file. Finally, the cyber actor deletes the text file from the temp directory and executes the .BAT file.
According to MITRE, KONNI uses the ATT&CK techniques listed in table 1.
Table 1: KONNI ATT&CK techniques
CISA developed the following Snort signatures for use in detecting KONNI malware exploits.
CISA recommends that users and administrators consider using the following best practices to strengthen the security posture of their organization's systems. Any configuration changes should be reviewed by system owners and administrators prior to implementation to avoid unwanted impacts.
For additional information on malware incident prevention and handling, see the National Institute of Standards and Technology Special Publication 800-83, "Guide to Malware Incident Prevention and Handling for Desktops and Laptops."
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Summary
This Alert uses the MITRE Adversarial Tactics, Techniques, and Common Knowledge (ATT&CK®) framework. See the ATT&CK for Enterprise framework for all referenced threat actor techniques.
The Cybersecurity and Infrastructure Security Agency (CISA) has observed cyber actors using emails containing a Microsoft Word document with a malicious Visual Basic Application (VBA) macro code to deploy KONNI malware. KONNI is a remote administration tool (RAT) used by malicious cyber actors to steal files, capture keystrokes, take screenshots, and execute arbitrary code on infected hosts.
Technical Details
KONNI malware is often delivered via phishing emails as a Microsoft Word document with a malicious VBA macro code (Phishing: Spearphising Attachment [T1566.001]). The malicious code can change the font color from light grey to black (to fool the user to enable content), check if the Windows operating system is a 32-bit or 64-bit version, and construct and execute the command line to download additional files (Command and Scripting Interpreter: Windows Command Shell [T1059.003]).
Once the VBA macro constructs the command line, it uses the certificate database tool CertUtil to download remote files from a given Uniform Resource Locator. It also incorporates a built-in function to decode base64-encoded files. The Command Prompt silently copies
certutil.exe into a temp directory and renames it to evade detection.The cyber actor then downloads a text file from a remote resource containing a base64-encoded string that is decoded by CertUtil and saved as a batch (.BAT) file. Finally, the cyber actor deletes the text file from the temp directory and executes the .BAT file.
MITRE ATT&CK Techniques
According to MITRE, KONNI uses the ATT&CK techniques listed in table 1.
Table 1: KONNI ATT&CK techniques
| Technique | Use |
|---|---|
KONNI can collect the Internet Protocol address from the victim’s machine. | |
KONNI can collect the username from the victim’s machine. | |
KONNI creates a shortcut called Anti virus service.lnk in an apparent attempt to masquerade as a legitimate file. | |
Exfiltration Over Alternative Protocol: Exfiltration Over Unencrypted/Obfuscated Non-C2 Protocol [T1048.003] | KONNI has used File Transfer Protocol to exfiltrate reconnaissance data out. |
KONNI has the capability to perform keylogging. | |
KONNI has used tasklist.exe to get a snapshot of the current processes’ state of the target machine. | |
KONNI used PowerShell to download and execute a specific 64-bit version of the malware. | |
KONNI has used cmd.exe to execute arbitrary commands on the infected host across different stages of the infection change. | |
KONNI can delete files. | |
KONNI has used Hypertext Transfer Protocol for command and control. | |
KONNI can gather the operating system version, architecture information, connected drives, hostname, and computer name from the victim’s machine and has used systeminfo.exe to get a snapshot of the current system state of the target machine. | |
A version of KONNI searches for filenames created with a previous version of the malware, suggesting different versions targeted the same victims and the versions may work together. | |
KONNI can download files and execute them on the victim’s machine. | |
KONNI has modified registry keys of ComSysApp service and Svchost on the machine to gain persistence. | |
KONNI can take screenshots of the victim’s machine. | |
KONNI had a feature to steal data from the clipboard. | |
KONNI has used a custom base64 key to encode stolen data before exfiltration. | |
KONNI has duplicated the token of a high integrity process to spawn an instance of cmd.exe under an impersonated user. | |
KONNI has used CertUtil to download and decode base64 encoded strings. | |
KONNI has used Rundll32 to execute its loader for privilege escalation purposes. | |
KONNI has modified ComSysApp service to load the malicious DLL payload. | |
A version of KONNI drops a Windows shortcut into the Startup folder to establish persistence. | |
A version of KONNI drops a Windows shortcut on the victim’s machine to establish persistence. | |
KONNI bypassed User Account Control with the "AlwaysNotify" settings. | |
KONNI can steal profiles (containing credential information) from Firefox, Chrome, and Opera. |
Detection
Signatures
CISA developed the following Snort signatures for use in detecting KONNI malware exploits.
alert tcp any any -> any $HTTP_PORTS (msg:"HTTP URI contains '/weget/*.php' (KONNI)"; sid:1; rev:1; flow:established,to_server; content:"/weget/"; http_uri; depth:7; offset:0; fast_pattern; content:".php"; http_uri; distance:0; within:12; content:!"Referrer|3a 20|"; http_header; classtype:http-uri; priority:2; metadata:service http;)alert tcp any any -> any $HTTP_PORTS (msg:"KONNI:HTTP header contains 'User-Agent|3a 20|HTTP|0d 0a|'"; sid:1; rev:1; flow:established,to_server; content:"User-Agent|3a 20|HTTP|0d 0a|"; http_header; fast_pattern:only; content:"POST"; nocase; http_method; classtype:http-header; priority:2; metadata:service http;)alert tcp any any -> any $HTTP_PORTS (msg:"KONNI:HTTP URI contains '/weget/(upload|uploadtm|download)'"; sid:1; rev:1; flow:established,to_server; content:"/weget/"; http_uri; fast_pattern:only; pcre:"/^\/weget\x2f(?:upload|uploadtm|download)\.php/iU"; content:"POST"; http_method; classtype:http-uri; priority:2; reference:url,blog.talosintelligence.com/2017/07/konni-references-north-korean-missile-capabilities.html; metadata:service http;)Mitigations
CISA recommends that users and administrators consider using the following best practices to strengthen the security posture of their organization's systems. Any configuration changes should be reviewed by system owners and administrators prior to implementation to avoid unwanted impacts.
- Maintain up-to-date antivirus signatures and engines. See Link Removed.
- Keep operating system patches up to date. See Link Removed.
- Disable file and printer sharing services. If these services are required, use Link Removed or Active Directory authentication.
- Restrict users' ability (permissions) to install and run unwanted software applications. Do not add users to the local administrators’ group unless required.
- Enforce a strong password policy. See Link Removed.
- Exercise caution when opening email attachments, even if the attachment is expected and the sender appears to be known. See Link Removed.
- Enable a personal firewall on agency workstations, configured to deny unsolicited connection requests.
- Disable unnecessary services on agency workstations and servers.
- Scan for and remove suspicious email attachments; ensure the scanned attachment is its "true file type" (i.e., the extension matches the file header).
- Monitor users' web browsing habits; restrict access to sites with unfavorable content.
- Exercise caution when using removable media (e.g., USB thumb drives, external drives, CDs).
- Scan all software downloaded from the internet prior to executing.
- Maintain situational awareness of the latest threats and implement appropriate access control lists.
- Visit the MITRE ATT&CK Techniques pages (linked in table 1 above) for additional mitigation and detection strategies.
For additional information on malware incident prevention and handling, see the National Institute of Standards and Technology Special Publication 800-83, "Guide to Malware Incident Prevention and Handling for Desktops and Laptops."
Resources
Revisions
- August 14, 2020: Initial Version
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