The ASEC analysis team 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 November 20th, 2022 to November 26th, 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. Additionally, the type that leaks login account credentials will be defined as FakePage.
During this week, the most prevalent threat type seen in phishing email attachments was Infostealer, taking up 34%. Infostealer includes malware such as AgentTesla and FormBook, and they leak user credentials saved in web browsers, emails, and FTP clients.
It was then followed by fake login pages (FakePage), which took up 21%. FakePages are web pages where the threat actor has imitated the screen layout, logo, and font of the real website, leading users to enter their account and password information. The input information is sent to the threat actor’s C2 server.See <Fake Login Page C2> below
Aside from these, Trojan (15%), Backdoor (10%), Worm (8%), Downloader (7%), and Exploit (2%) 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. As FakePages are web page scripts that must be executed with a web browser, they were distributed with HTML, SHTML, and HTM file extensions. Other malware, including Infostealer and downloader, came attached to emails with various file extensions including compressed files (ZIP, R07, RAR, XZ, etc.), IMG disk image files, and XLS document files. With the exception of fake login pages which have to be web page script files, other malware were distributed with a variety of file extensions regardless of the threat type.
Cases of Distribution
The following are the distribution cases that occurred during the week from November 20th, 2022, to November 26th, 2022. The cases will be classified into fake login pages 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 the identical English subject and text.
Case: Fake Login Pages (FakePage)
|A/R Invoice – 1058071||AR Invoice – 1058071.htm|
|FW: Documents? INVOICE AND STATEMENT||Documents.htm|
|FW: Purchase Order||Quote.html|
|Invoice Confirmation||Invoice (1).html|
|P.O9035 Payment for ***.com: Wednesday, November 23, 2022||OptoSort_GmbH_P.O24365.html|
|Payment Advise – Thursday, November 24, 2022||ian.tolfree_Payment Schedule-PL-PG-19703507.file.html|
|Re: Re: Request of Quotation.||new-order P.o.html|
|Your mailbox is 98% full.||Storage Settings.html|
|Fwd: attached invoice for balance payment||Invoice settlement.shtml|
Case: Malware (Infostealer, Downloader, etc.)
|Balanced payment for invoice 058418||image004.img|
|DHL Shipment Notification 4816 Custom Form E||CUSTOM CLEARNCE FORM E.xls|
|Inquiry HA-22-28199 22-077 for Mongolian Market||Inquiry HA-22-28199 22-077,pdf.img|
|Inquiry HA-22-28199 22-077 for Mongolian Market||Inquiry HA-22-28199 22-077.xls|
|New PO-SO210014-024||New PO-SO210014-024.xls|
|Re New Order 87012||NEW ORDER 87012_PDF.IMG|
|RE REVISED ORDER CONFIRMATION||PURCHASE.ORDER.IMG|
|Re Transferencia PAGO TT||Transferencia.pdf.img|
|REBBND List as on dt.18112022_20221118_2129.eml||BBND.IMG|
|REQUEST FOR QUOTATION Ref. # IRQ2107778||RFQ Ref. # IRQ2107778.img|
|Send email Invoice_04188.8.131.522||Invoice_04184.108.40.2062.img|
|Re: very sexy images only for you||wild__plp.exe|
|super wonderful picture don’t show||sex-act.exe|
|RE: MW90_CRF Port Klang_HongKong Taisung Innovase Enterprise Co. Ltd||MW90 CRF Port Klang_HongKong Taisung Innovase Enterprise Co. Ltd.r07|
|RE: NEW CONTRACT NO. 002/PPI/2/INV22100401||PPI_002_TUMINH_SIGNED_pdf.rar|
|Kindly Quote items||RFQ002511.rar|
|Kindly Quote items||Sheet001ESMPC1125.rar|
|TNT Express Invoice: 09004105 – Account: 000011320||TNT Invoice_pdf.xz|
|SAMPLE FOR REQUEST||TESN REQUEST SAMPLE.z|
|Fwd: REMITTANCES||REMITTANCE COPY – Nov 2022.zip|
|New Shipment notifice||SHIPPING DOC.zip|
|Arrange balance payment||Proof of payment.zip|
|DHL AWB – 4520065422||DHL AWB – 4520065422_Nov.2022.zip|
|Fwd: AW: Re: REMITTANCES||REMITTANCE COPY#900024415xxxx2022.zip|
|NEW DECEMBER ORDER PO#137810205||NEW_ORDER_PO137810205.pdf.zip|
|BANK DETAILS CONFIRMATION||swift(USD 17043.50).zip|
Based on the above distribution cases, the ASEC analysis team selected keywords that users must look out for. If these keywords are included in the subject of the email, or if characteristics similar to the keywords are found, users must exercise strict caution as they may be phishing emails from threat actors.
Keywords to Beware of: ‘Payment’, ‘Invoice’
There were multiple malicious emails that disguised themselves as having been sent from certain companies by using transaction-related keywords such as ‘invoice‘ and ‘payment.’ The email below is attached with an IMG file named ‘image004.img.’ Disk image files (IMG) are the most widely distributed type at the moment, and they have a malicious executable inside, which is PureCrypter malware classified as a downloader.
Fake Login Page (FakePage) C2 URL
When users enter their IDs and passwords on the fake login page 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.
Preventing Phishing Email Attacks
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 antivirus software.
According to the MITRE ATT&CK framework, phishing email attacks correspond to the following techniques.
- Phishing for Information (Reconnaissance, ID: T1598)
- Phishing (Initial Access, ID: TI1566)
- Internal Spearphishing (Lateral Movement, ID: T1534)
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