Space after Filename

Space after Filename [T1036.006]

Information

• Name: Space after Filename

• ID: T1036.006

• Tactics: TA0005

• Technique: T1036

Introduction

The "Space after Filename" sub-technique (T1036.006) falls under the "Masquerading" technique (T1036) within the MITRE ATT&CK framework. Attackers leverage this sub-technique to disguise malicious executables by adding extra whitespace after filenames, thereby misleading users and administrators into believing the file is legitimate or harmless. The primary goal is to evade detection and increase the likelihood of successful execution.

Deep Dive Into Technique

Attackers using the "Space after Filename" sub-technique rely on the visual ambiguity created by whitespace characters at the end of filenames. In many operating systems and user interfaces, trailing spaces are either difficult to notice or completely invisible, allowing attackers to masquerade malicious executables as benign files.

Technical details and execution methods include:

• Filename Manipulation: Attackers append whitespace characters (spaces) after the filename and before the file extension. For example, a malicious executable named invoice.pdf.exe can become visually indistinguishable from a legitimate file if renamed to invoice.pdf .exe, especially when file extensions are hidden or truncated by the operating system's file explorer.

• User Interface Exploitation: Default settings in operating systems such as Windows often hide file extensions, further exacerbating the confusion. Users may see invoice.pdf instead of the full filename, failing to recognize the file as an executable.

• Unicode and Encoding Tricks: Attackers may employ Unicode characters that resemble whitespace or legitimate filename characters, further complicating visual identification.

• File System Behavior: Certain file systems or file explorers may ignore or collapse trailing whitespace, making the malicious file visually identical to legitimate files.

When this Technique is Usually Used

Attackers typically use the "Space after Filename" sub-technique in multiple attack scenarios and stages, including:

• Initial Access and Delivery Stage:

  • Phishing campaigns involving attachments disguised as legitimate documents (e.g., invoices, resumes, reports).

  • Malicious downloads from compromised websites or file-sharing platforms.

• Execution Stage:

  • Encouraging users to open disguised executables, leading to malware execution and infection.

• Persistence and Lateral Movement:

  • Deploying disguised executables on compromised systems to maintain persistence without raising suspicion.

  • Distributing malicious files across network shares to infect additional endpoints.

• Social Engineering Attacks:

  • Exploiting user trust in known document formats (PDF, DOCX, XLSX) to trick users into executing malicious payloads.

How this Technique is Usually Detected

Detection of the "Space after Filename" sub-technique typically involves a combination of endpoint monitoring, behavioral analysis, and user-awareness strategies. Effective detection methods and indicators of compromise (IoCs) include:

• Endpoint Detection and Response (EDR) Solutions:

  • Monitoring for anomalous file naming patterns, especially trailing whitespace or unusual Unicode characters.

  • Tracking file execution patterns and alerting on suspicious filename structures.

• File Integrity Monitoring (FIM):

  • Identifying files with trailing spaces or hidden extensions within critical directories.

  • Generating alerts for newly created or modified files exhibiting suspicious naming conventions.

• Security Information and Event Management (SIEM):

  • Aggregating logs from file systems and endpoint security tools to detect anomalies related to filename manipulation.

  • Creating correlation rules to identify suspicious file executions based on naming patterns.

• User Awareness and Training:

  • Educating users to recognize suspicious filenames, especially those with unusual spacing or hidden extensions.

  • Encouraging users to enable the display of file extensions within the operating system's file explorer.

Specific IoCs to look for:

• Files with trailing whitespace characters before the executable extension (e.g., .exe, .bat, .scr).

• Executable files named similarly to common document formats (e.g., .pdf, .docx) but with hidden executable extensions.

• Unusual activity logs indicating execution of files with suspicious naming conventions.

Why it is Important to Detect This Technique

Early detection of the "Space after Filename" sub-technique is critical due to the potential risks and impacts associated with successful exploitation:

• Malware Infection:

  • Successful execution can lead to the installation of malware, including ransomware, spyware, keyloggers, or remote access trojans (RATs).

• Data Breach and Exfiltration:

  • Attackers may leverage disguised executables to gain initial access and subsequently exfiltrate sensitive data from compromised systems.

• Operational Disruption:

  • Malware deployment may lead to downtime, loss of productivity, data corruption, and operational disruptions.

• Lateral Movement and Persistence:

  • Undetected malicious executables can facilitate attacker persistence within the network, enabling lateral movement and further compromise of critical systems.

• Reputational Damage:

  • Successful attacks using this technique can result in significant reputational harm, loss of customer trust, and potential regulatory penalties.

Early detection and mitigation reduce the likelihood of extensive damage, limit attacker presence within the environment, and facilitate rapid incident response and remediation.

Examples

Real-world examples and attack scenarios involving the "Space after Filename" sub-technique include:

• Phishing Campaigns:

  • Attackers send emails with attachments named invoice.pdf .exe or resume.doc .exe, tricking recipients into executing malicious payloads.

  • Users, seeing only invoice.pdf or resume.doc due to hidden file extensions, unknowingly execute malware that installs ransomware or spyware.

• Malicious Downloads from Compromised Websites:

  • Attackers host malicious files on compromised or fake websites, naming them similarly to legitimate software or documents.

  • Users downloading files such as setup.exe disguised as setup .exe inadvertently execute malware.

• APT Group Activities:

  • Advanced Persistent Threat (APT) groups have been observed employing filename manipulation techniques, including trailing spaces, to evade user detection and deploy malware onto corporate networks.

• Tools and Malware Samples:

  • Malware families such as Emotet, TrickBot, and Qakbot have utilized similar masquerading techniques to deliver payloads.

  • Attackers commonly use standard system utilities and scripting languages (PowerShell, VBScript) to automate the renaming and distribution of disguised executables.

Impacts observed in these scenarios include:

• Successful ransomware infections causing extensive operational disruption.

• Theft of sensitive data resulting in financial losses and regulatory fines.

• Persistent attacker footholds leading to long-term compromises and advanced attacks against targeted organizations.