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Email Threat Review September 2021

Written by Security Lab / 14.10.2021 /
Home » Blog » Email Threat Review September 2021

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

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

Email category%
Rejected80.83
Spam14.15
Threat4.07
AdvThreat0.91
Content0.03

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:

CategoryDescription
SpamThese emails are unwanted and are often promotional or fraudulent. The emails are sent simultaneously to a large number of recipients.
ContentThese emails have an invalid attachment. The administrators define in the Content Control module which attachments are invalid.
ThreatThese emails contain harmful content, such as malicious attachments or links, or they are sent to commit crimes like phishing.
AdvThreatAdvanced Threat Protection has detected a threat in these emails. The emails are used for illegal purposes and involve sophisticated technical means that can only be fended off using advanced dynamic procedures.
RejectedOur email server rejects these emails directly during the SMTP dialog because of external characteristics, such as the sender’s identity, and the emails are not analyzed further.

File types used in attacks

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

File type (used in malicious emails)%
HTML37.2
Archive28.8
PDF11.3
Excel6.4
Disk image files4.6
Other4.0
Word3.7
Executable3.5
Powerpoint0.2
Script file0.2

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).

IndustriesShare of threat in threat and clean emails
Manufacturing industry6.0
Research industry5.7
Media industry5.3
Healthcare industry5.2
Automotive industry5.1
Education industry5.1
Transport industry5.0
Construction industry4.9
Mining industry4.9
Retail industry4.4

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.

Attack technique%
Other39.0
Phishing29.1
Impersonation10.3
URL10.0
Advance-fee scam3.5
Extortion3.1
Executable in archive/disk-image3.1
Maldoc1.9

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.

Impersonated brand or organization%
Sparkasse19.7
Volks- und Raiffeisenbank15.0
Deutsche Post / DHL13.5
DocuSign12.5
Other11.3
Amazon8.9
PayPal4.6
LinkedIn1.9
Microsoft1.7
UPS1.3
HSBC1.1

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:

Leak siteNumber of victim data leaks
Conti40
LockBit 2.034
Pysa15
Everest8
Vice Society7
Hive5
REvil5
RansomEXX3
Lorenz1

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

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