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Security advisories — Apr 11, 2023

Increase in Observations of Qakbot Malware 

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In the first week of April 2023, the eSentire Threat Intelligence team observed a significant increase in Qakbot incidents impacting various industries. Qakbot is an information-stealing malware. Qakbot is commonly delivered using phishing methods, including malicious emails from previously unseen email addresses or as replies to existing email conversations.   

In these incidents, Qakbot gained initial access through phishing emails containing a Zip archive containing a Windows script file (.wsf), a PDF document, or an HTML file using the HTML smuggling method. The malware can also retrieve CobaltStrike from a command-and-control site, and perform basic reconnaissance. However, observed attacks were isolated and alerted on, and the customers were notified for remediation.   

Qakbot is highly concerning as the malware has been observed leading to the delivery of multiple ransomware variants. eSentire is sharing details on these attacks, including indicators of compromise (IOCs), to increase awareness of this threat across our customers. 

What we’re doing about it

What you should do about it

Additional information

Qakbot malware has been in active use since at least 2007 [1]. Initially, the malware was used to steal victim data, but in recent years it has functioned primarily for reconnaissance and ransomware delivery.

In recently observed incidents, Qakbot was identified gaining initial access through phishing emails. The users received either a Zip archive containing a Windows Script file (.wsf), a PDF document, or an HTML file where they utilized the HTML smuggling method.  This is a notable change from the February Qakbot campaign, where all observed threats were delivered via malicious OneNote attachments. It is likely that threat actors distributing Qakbot are testing alternative delivery mechanisms, as Microsoft announced new security measures that will be applied to Microsoft 365 to combat OneNote abuse starting in April 2023.

In the first pair of incidents, eSentire MDR for Endpoint was able to block the activity from continuing past the initial file execution. eSentire MDR for Endpoint also blocked the activity as it reached the PowerShell scripting stage, which involved a PowerShell script attempting to reach domains associated with a Qakbot infection.

In later observed incidents, eSentire identified a version of Qakbot that retrieved Cobalt Strike immediately. If not identified and remediated immediately, the malware would load Cobalt Strike into the machine's registry and perform basic reconnaissance, though eSentire MDR for Endpoint was able to block any connections attempted. The Cobalt Strike framework is a common ransomware precursor threat.

In all recent incidents, eSentire's proactive threat intelligence feeds and global block lists detected activity on the hosts, which were isolated, alerted, and escalated to the customers for remediation. Due to rapid remediation, secondary payloads and attacker objectives have not been identified.

Indicators of Compromise (IoCs):

Type IoC Description
IP Address 23[.]81[.]246[.]2 Cobalt Strike
IP Address 94[.]131[.]117[.]111 Qakbot
IP Address 199[.]247[.]30[.]203 Qakbot
IP Address 141[.]94[.]86[.]90 Qakbot
IP Address 104[.]225[.]129[.]114 Qakbot
IP Address 216[.]146[.]25[.]129 Qakbot
IP Address 85[.]239[.]41[.]205 Qakbot
File 6291579CD41491CC045D7E0ED05B9A3A72C5CCA6F74F8BDEBC1C85459C423B60 Cobalt Strike
File 8C8CF24571C836636A25040CE36EEA9036B0CC4F09DA14780ED2618A488FDFE8 Qakbot
File EC3F1349AC0196FF3EBCC30435B16B7E290FA8C2FDC0223F72AD9BC08C7B4486 Qakbot
File 0A354C9637EFA27F5B41A525574CB8FC496677E16CE06832CCF0AF699FCCEECA Qakbot


[1] https://attack.mitre.org/software/S0650/
[2] https://www.esentire.com/security-advisories/new-qakbot-campaign-observed
[3] https://www.microsoft.com/en-us/security/blog/2021/11/11/html-smuggling-surges-highly-evasive-loader-technique-increasingly-used-in-banking-malware-targeted-attacks/
[4] https://www.esentire.com/security-advisories/ongoing-qakbot-onenote-campaign
[5] OneNote blocks embedded files that have dangerous extensions - Deploy Office | Microsoft Learn

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