Brinztech Alert: The Alleged SMTP of Various Japanese Websites are on Sale

Dark Web News Analysis

The dark web news reports a widespread infrastructure threat targeting the Japanese Digital Ecosystem. A threat actor on a hacker forum is selling valid SMTP (Simple Mail Transfer Protocol) access credentials for several major Japanese internet service providers and hosting platforms.

The affected domains include heavyweights such as Nifty.com, Heteml.jp, Lolipop.jp, Biglobe.ne.jp, Sakura.jp, Commufa.jp, and Xserver.jp. The credentials are being sold for prices ranging from $30 to $50 per account. This low price point suggests a high volume of available accounts, likely harvested through malware (stealer logs) or brute-force attacks on weak passwords.

Key Cybersecurity Insights

Breaches of ISP and hosting provider SMTPs are “Tier 1” email security threats because they bypass the “Trust Barrier” of spam filters:

• High-Reputation Phishing: The primary value of these accounts is their Domain Reputation. Emails sent from Biglobe.ne.jp or Sakura.jp are trusted by spam filters (Google, Outlook, Yahoo) because they come from legitimate, high-reputation infrastructure. Attackers use this “Clean IP” status to land phishing emails directly in the victim’s Primary Inbox, bypassing the Junk folder.
• Business Email Compromise (BEC): Many small and medium-sized Japanese businesses use these providers for their corporate email. Hijacking an SMTP account allows an attacker to insert themselves into existing email threads, sending fake invoices or changing bank account details from a legitimate address.
• Malware Distribution: Because the sender domain is trusted, attachments sent via these SMTPs are less likely to be blocked by antivirus gateways. Attackers can mass-mail ransomware or banking trojans (like Emotet) to thousands of users in Japan.
• “From” Header Spoofing: With direct SMTP access, attackers can often manipulate the “From” header to impersonate government agencies or banks, while the underlying technical headers show the email originated from a valid Japanese server, confusing security analysts.

Mitigation Strategies

To protect email integrity and prevent domain abuse, the following strategies are recommended:

• Strict Authentication Protocols: The affected providers and their business clients must enforce DMARC (Reject Policy), SPF, and DKIM. This ensures that even if an attacker has SMTP access, unauthorized emails failing cryptographic checks are blocked or flagged.
• Outbound Traffic Analysis: ISPs like Nifty and Biglobe should implement rate-limiting and anomaly detection on outbound SMTP traffic. A sudden spike in emails from a residential or small business account is a clear indicator of compromise.
• Password Reset Campaign: Force immediate password resets for users identified in the breach or those with suspicious login patterns (e.g., logins from non-Japanese IP addresses).
• MFA for Mail Access: Enforce Multi-Factor Authentication (MFA) not just for webmail, but for SMTP/IMAP authentication where supported, to prevent automated credential abuse.

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