ASEC Weekly Phishing Email Threat Trends (June 4th 2023 – June 10th, 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 June 4th, 2023 to June 10th, 2022 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 Downloader with 37%. Downloaders downloaded various additional malware such as Infostealers and backdoors. The second most prevalent type was Infostealers (29%) like AgentTesla, FormBook, and AveMaria, that leak user credentials saved in web browsers, emails, and FTP clients. It was then followed by FakePages (18%), which 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. Aside from those mentioned above, Trojan (15%) and Exploit (1%) types 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, SHTM, 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, Z, GZ, 7Z, etc.).

Cases of Distribution

The following are distribution cases that occurred during the week from June 4th, 2023 to June 10th, 2022. 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.

Keywords to Beware of: ‘Hometax Tax Bill’

The keywords for this week are ‘Hometax Tax Bill’. May is the month of filing the general income tax in Korea. Following this, the threat actor impersonated the National Tax Service to distribute the GuLoader malware to multiple normal users. Inside the attached compressed file “NTS_eTaxInvoice-pdf.zip” is an EXE-type GuLoader with the same file name. This malware is a downloader that additionally downloads a backdoor or an Infostealer. At the time of analysis, the NanoCore RAT tool was downloaded, and the threat actor can take remote control of user PCs with this tool. As such, when opening attachments in emails, users must check their sources and be cautious of opening executable files such as those with the EXE extension.

NTS_eTaxInvoice-pdf.exe (ED9A4BBACD25426E9403E7847619F5BE) V3 file detection information/engine version – Trojan/Win.GuLoader.R585076 (2023.06.07.02)

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[:]//regulateantelope[.]sa[.]com/slim/fdpxoGur23f[.]php
• https[:]//regulateantelope[.]sa[.]com/funn/fdpxoGur23f[.]php
• https[:]//sattaonmobile[.]com/new/1drv[.]php
• https[:]//submit-form[.]com/ghJmPlKG
• https[:]//naehpa[.]com/wp-admin/xX/frehot[.]php
• https[:]//californiaapostillenotary[.]com/wp-admin/AA/fedex[.]php
• https[:]//formspree[.]io/f/xoqzoajq
• https[:]//naehpa[.]com/wp-admin/QY/port25[.]php
• https[:]//submit-form[.]com/GPg6ZA4G
• http[:]//175[.]178[.]24[.]223/wp-content/themes/finl/lead/access1[.]php
• https[:]//formspree[.]io/f/myyazkbv
• https[:]//submit-form[.]com/XLknrnS0

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])

Subscribe to AhnLab’s next-generation threat intelligence platform ‘AhnLab TIP’ to check related IOC and detailed analysis information.