ASEC Weekly Phishing Email Threat Trends (April 23rd, 2023 – April 29th, 2023)

AhnLab Security Emergency response Center (ASEC) monitors phishing email threats with the ASEC automatic sample analysis system (RAPIT) and honeypot. This post will cover the cases of distribution of phishing emails during the week from April 23rd, 2023 to April 29th, 2023 and provide statistical information on each type. Generally, phishing is cited as an attack that leaks users’ login account credentials by disguising as or impersonating an institute, company, or individual through social engineering methods. On a broader note, the act is a technical subterfuge that enables the threat actor to perform attacks such as information leaks, malware distribution, and fraud against various targets. The focus of this post will be on the fact that phishing attacks mainly occur through emails. We will also provide a detailed classification of various attack methods that are based on phishing emails. Furthermore, we will make an effort to minimize user damage by introducing new attack types that have never been found before and emails that require users’ caution, along with their keywords. The phishing emails covered in this post will only be those that have attachments. Emails that have malicious links in the body without attachments will be excluded.

Phishing Emails

During this week, the most prevalent threat type seen in phishing email attachments was FakePage with 62%. FakePages are web pages where the threat actor has imitated the screen layout, logo, and font of the real login pages or advertising pages, leading users to enter their account and password information. The input information is sent to the threat actor’s C2 server or used to induce users to access other fake websites. ^{See <FakePage C2> below} The second in line were InfoStealers like AgentTesla and FormBook that leaks user credentials saved in web browsers, emails, and FTP clients (15%). It was then followed by Worm, which took up 11%. Worm is a type of malware that has a feature to spread, where it uses various methods for spreading, with one of them being using the SMTP protocol to send emails in mass quantity. Aside from those mentioned above, Trojan (6%), Exploit (3%), and Downloader (3%) were detected. The threat types using phishing email attachments and their order of prevalence are similar to the order of malware distribution published weekly in the <ASEC Weekly Malware Statistics>.

File Extensions in Phishing Emails

We have identified which file extensions were used by the threats above for the distribution of email attachments. FakePages were distributed through web pages script (HTM, HTML, SHTML) documents that must be executed with a web browser. Other malware, including Infostealer and downloader, came attached to emails with file extensions including compressed files (RAR, ZIP, 7Z, GZ, etc.).

Cases of Distribution

The following are distribution cases that occurred during the week from April 23rd, 2023 to April 29th, 2023. The cases will be classified into FakePage and malware types, including Infostealer, Downloader, Exploit, and Backdoor. The numbers in email subjects and attachment filenames are unique IDs and may vary depending on the email recipient. Distribution cases with Korean subjects were also found. These are cases that specifically targeted Korean users instead of propagating themselves globally using identical English subject and texts.

Case: FakePage

Case: Malware (Infostealer, Downloader, etc.)

The ASEC analysis team has selected keywords that users must look out for, based on the distribution cases above. If these keywords are included in the subject of the email, or if the same characteristics are found, users must exercise strict caution as they may be phishing emails from threat actors.  

Keyword to Beware of: ‘Disguised Image File’

The keyword for this week is ‘Disguised Image File.’ The Worm-type malware disguised as image files (coolimg.gif.pif) has been found among phishing email types. Threat actors arouse the curiosity of users through eye-catching messages to entice users into executing the malware disguised as an image file. As shown below, the file was distributed with the extension pif. This is an executable file just like the EXE extension.  As such, users are advised to take closer looks at the file names of email attachments before opening them and also check if the attachments are related to the subject of the email.

FakePage C2 URL

When users enter their IDs and passwords on the login pages among the FakePages created by the threat actor, their information is sent to the attacker’s server. The list below shows the threat actor’s C2 addresses of fake login pages distributed during the week.

• https[:]//formspree[.]io/f/myyazkbv
• https[:]//formspree[.]io/f/xayznrae
• https[:]//press[.]genesis[.]ru/zeta/xlss[.]php
• https[:]//www[.]coupedusud[.]fr/upload/accueil/speed/next[.]php
• https[:]//drmaysilveira[.]com[.]br/wp-content/onyi/excelz/index[.]php
• https[:]//anmelden[.]ml/[.]well-known/ac/pdf[.]php
• https[:]//steelfirst[.]com[.]au/new/1drv[.]php
• https[:]//tinyurl[.]com/bdfavnm7
• https[:]//press[.]genesis[.]ru/ziv/xlss[.]php

Attacks using phishing emails are disguised with content that can easily deceive users, such as invoices and tax payments, to induce users to access fake login pages or execute malware. Fake login pages are evolving by the second to closely resemble the original pages. The attackers pack malware in compressed file formats to escape the attachment scans of users’ security products. Users must practice strict caution and refer to recent cases of distribution to avoid being exposed to infection by malicious phishing emails. The ASEC analysis team recommends users follow the email security guidelines below.

• Do not execute links and attachments in emails from unverified senders until they are proven to be credible.

• Do not enter sensitive information such as login account credentials until the site is found to be reliable.

• Do not execute attachments with unfamiliar file extensions until they are found to be reliable.

• Use security products such as antimalware software.

According to the MITRE ATT&CK framework, phishing email attacks correspond to the following techniques.

• Phishing for Information(Reconnaissance, ID: T1598^[1])

• Phishing(Initial Access, ID: TI1566^[2])

• Internal Spearphishing(Lateral Movement, ID:T1534^[3])

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