Protection Guide: RedLine Stealer

Attack Vectors to Block

RedLine Stealer primarily spreads through social engineering and software bundling. Blocking these vectors requires a layered approach.

Phishing Emails and Malicious Attachments: RedLine is frequently distributed via phishing campaigns using password-protected ZIP or RAR archives (e.g., invoice.zip, document.rar) containing malicious executables or script files. At the email gateway, enforce policies to block or sandbox all executable attachments and archive files, especially those with passwords. On the endpoint, configure application control to prevent execution from temporary download directories like %TEMP% or %USERPROFILE%\Downloads.

Malvertising and Drive-by Downloads: Attackers use compromised websites or malicious advertisements to redirect users to sites hosting RedLine payloads, often disguised as software installers or updates. Implement web filtering at the proxy or firewall level to block access to known malicious domains and newly registered domains (NRDs). Use browser isolation or security plugins to prevent unauthorized downloads.

Fake Software and Cracked Applications: RedLine is bundled with pirated software, game cheats, and fake cracks distributed on torrent sites and unofficial forums. Network controls should block access to common piracy and crack distribution sites. Endpoint policies should restrict the installation of unauthorized software and monitor for execution of installers from non-standard locations.

Initial Execution via Scripts: RedLine droppers often use PowerShell, VBScript, or batch files to download and execute the final payload. Disable or heavily restrict script execution on endpoints. For necessary administrative scripts, enforce code signing requirements and execution from approved, secured directories only.

Email Security Configuration

Configure your email security gateway with the following rules to intercept RedLine Stealer phishing attempts.

Attachment Filtering Policies:

• Block all email attachments with the following extensions: .exe, .scr, .ps1, .vbs, .js, .jar, .bat, .cmd.
• Quarantine all .zip, .rar, .7z, and other archive file types for manual inspection or advanced sandbox analysis. Pay special attention to archives that are password-protected, as this is a common tactic to evade automated scanning.
• Enable file type verification to detect executable files masquerading with double extensions (e.g., document.pdf.exe).

URL Defense and Link Analysis:

• Enable time-of-click URL scanning for all links within emails. Rewrite all URLs to pass through your secure web gateway for real-time categorization and threat detection.
• Block emails containing links to newly registered domains (less than 30 days old) or domains with a poor reputation score.
• Implement DMARC, DKIM, and SPF authentication checks to reduce spoofing and impersonation attempts that lend credibility to phishing lures.

Content and Sender Policies:

• Create high-priority content filters to flag emails with subjects or body text containing common RedLine lures: “Invoice”, “Payment Due”, “Document”, “Your Order”, “COVID-19”, or “Software Update”.
• Quarantine emails from external senders that contain macro-enabled documents (.docm, .xlsm) unless explicitly expected and from a verified sender.
• Configure your gateway to add a prominent external warning banner to all emails originating from outside your organization.

Endpoint Protection Tuning

Fine-tune your endpoint security stack to detect and block RedLine Stealer’s behaviors.

Behavioral Detection Rules:

• Create a rule to alert on processes that rapidly access credentials from multiple sources (browsers, email clients, FTP clients, cryptocurrency wallets) in a short timeframe.
• Enable detection for processes that attempt to disable security software or tamper with Windows Defender settings via registry modifications.
• Configure your EDR solution to flag processes that make outbound connections to IP addresses on non-standard ports (e.g., 8080, 8443) shortly after creation, a common C2 pattern.

Application Control and Hardening:

• Implement a robust application allowlisting policy. Deny execution of all binaries and scripts from high-risk locations: %APPDATA%, %LOCALAPPDATA%, %TEMP%, %USERPROFILE%\Downloads, and public writable shares.
• Restrict the use of system utilities for malicious purposes. Constrain powershell.exe, wscript.exe, cscript.exe, cmd.exe, and mshta.exe to execute only signed scripts or from specific, trusted parent processes.
• Disable Windows Script Host (wscript.exe and cscript.exe) via Group Policy for standard user workstations if not required for business functions.

Memory and Process Protection:

• Enable exploit protection features like Data Execution Prevention (DEP) and Arbitrary Code Guard (ACG) to prevent process injection techniques RedLine may use.
• Configure your endpoint solution to monitor for and block attempts at credential dumping from the lsass.exe process memory.

Network-Level Defenses

Block RedLine’s command-and-control (C2) communication and hinder its ability to exfiltrate data.

DNS Filtering and Sinkholing:

• Subscribe to and enforce threat intelligence feeds that provide domains and IPs associated with RedLine Stealer C2 servers. Current IOCs
• Configure your DNS filtering service to block requests to domains categorized as “Malware,” “Botnets,” and “Newly Seen Domains.”
• Implement DNS logging and alerting for endpoints making repeated queries to domains with a high entropy score (e.g., kjh123sdg[.]com), a common trait of algorithmically generated C2 domains.

Web Proxy/Content Filtering Rules:

• Block access to IP addresses and domains associated with common malware hosting services and free web hosting providers frequently abused by attackers.
• Block file downloads of executable (*.exe), script (*.ps1, *.vbs), and dynamic link library (*.dll) file types from the internet for standard users.
• Decrypt and inspect HTTPS traffic (where legally and technically feasible) to detect C2 beaconing or data exfiltration attempts hidden in encrypted channels.

Firewall and Network Segmentation:

• Enforce egress firewall rules that restrict outbound connections from user workstations to only necessary ports and services. Deny all outbound traffic on non-standard ports.
• Segment networks to prevent lateral movement. Ensure workstations cannot initiate connections to critical servers (like domain controllers or file servers) except for specific, authorized protocols.
• Deploy a network intrusion detection/prevention system (NIDS/NIPS) with rules tuned to detect the specific HTTP POST patterns and user-agent strings often used by RedLine for data exfiltration.

User Awareness Training Points

Educate users to recognize and avoid the social engineering tactics used to deploy RedLine Stealer.

Spotting Phishing Lures:

• Train users to be suspicious of unsolicited emails with urgent language pressuring them to open an attachment, especially invoices, shipping notices, or “security alerts.”
• Emphasize that legitimate organizations will never send password-protected archives via email without prior arrangement and explanation.
• Instruct users to never enable macros in documents received via email, even if prompted. RedLine often uses macro-laden documents as initial droppers.

Safe Software Practices:

• Stress that downloading software, cracks, or game cheats from unofficial sources (torrents, free download sites, forums) is a primary infection method. Distribution Methods
• Encourage users to only download software from official vendor websites and to verify the integrity of installers when possible.
• Teach users to look for subtle signs of fake software, such as poor grammar, misspellings on websites, and requests for excessive permissions during installation.

Reporting and Response:

• Create a simple, clear process for users to report suspicious emails or unexpected computer behavior (e.g., slow performance, unexpected pop-ups) to the IT security team immediately.
• Reinforce that quick reporting can prevent a single infection from becoming a widespread data breach.
• Conduct regular simulated phishing exercises that mimic RedLine delivery methods to keep awareness high and provide targeted feedback.

For more background on this threat, please see the RedLine Stealer Overview.