File pumping is a technique used by malware and ransomware that is used to artificially inflate the size of a file by injecting it with additional bytes to bypass cybersecurity tools. This technique can work because many cybersecurity tools have a feature to bypass file scanning of files beyond 100MB.

This technique is often used to modify legitimate applications with “pumped” variants and then replace the original on public servers. This modified edition is then used as a mule to distribute the malware and infect the victims device.

File Pumping: How It Works

In a file pumping attack, the adversary typically targets a vulnerable system by sending files or data streams that are intentionally inflated or altered. These modifications can have several objectives:

  1. Exceeding File Size Limits: Some file systems, networks, or applications may have specific file size limits to ensure optimal performance. By “pumping” a file beyond its set limits, an attacker may cause the application or system to behave unexpectedly, such as crashing, becoming unresponsive, or even triggering buffer overflows.
  2. Malicious Payload Delivery: Another common purpose of file pumping is to deliver a malicious payload. For instance, an attacker may manipulate an image, document, or archive file by adding extra, seemingly innocuous data, which might remain undetected by traditional security measures. Once the file reaches its destination, it can be executed or unpacked to deploy malware, ransomware, or any other type of malicious software.
  3. Evasion of Detection: File pumping can be used to evade detection by security solutions. By inflating a file’s size with redundant or extraneous data, attackers may bypass security systems that are designed to scan for specific malware signatures or analyze file behavior. If the file’s size or structure falls within the acceptable range, it might not trigger the alarm mechanisms built into traditional security tools, allowing the attacker to smuggle malicious code past defenses.
  4. Denial of Service (DoS): In some cases, the act of pumping files is specifically designed to overload systems or cause a denial of service. For example, if a file is pumped to an excessively large size, it may trigger a DoS condition by consuming too much system memory, overwhelming storage resources, or causing service outages. When file size limits are reached, systems may fail to process incoming requests or crash entirely, leading to service disruptions.
  5. Data Exfiltration: File pumping can also be part of a broader data exfiltration strategy. Attackers may manipulate files to smuggle out sensitive information in small increments, hidden within inflated files. By encoding data or embedding it within file structure changes, attackers can bypass traditional data leak prevention tools designed to detect large or direct exfiltration of data.

Types of File Pumping Attacks

Several types of file pumping attacks have been documented across various cybersecurity domains:

  1. File Size Overflows: By inflating files past a system’s file size limit, attackers can trigger overflow vulnerabilities in software or services that don’t handle large files correctly. This can cause buffer overflows, leading to memory corruption, crashes, or the execution of arbitrary code.
  2. File Padding: Attackers may insert large amounts of benign-looking data into files, inflating their size without altering the contents. This padding can allow the attacker to evade file-based detection systems, which may only scan a certain portion of the file or miss irregularities in data structures caused by padding.
  3. File Fragmentation: Fragmenting files or using specific formats in a way that they appear legitimate on the surface but are actually fragmented across multiple locations or sections can be a form of file pumping. This technique can make it harder for security systems to scan files efficiently, increasing the chances of evasion.
  4. Encoding and Obfuscation: This method involves encoding or obfuscating malicious data within otherwise normal files. By changing the encoding format or structure of a file (e.g., embedding executable code inside image files or videos), an attacker can cause the file to be “pumped” with malicious content without triggering typical security scans or heuristics.

Risks and Impact of File Pumping

The risks associated with file pumping can vary depending on the nature of the attack and the target environment. However, common potential consequences include:

  1. System Downtime and Service Interruptions: If file pumping leads to memory overflows or crashes, systems may experience outages or prolonged downtimes. This is especially damaging in critical infrastructure or for services that rely on constant uptime, such as e-commerce platforms, banking systems, or healthcare environments.
  2. Malware Deployment: When file pumping is used to hide malicious payloads, the consequences can be severe. Malware, ransomware, and spyware can be delivered in this manner, often with the aim of stealing data, encrypting files for ransom, or gaining unauthorized access to sensitive systems.
  3. Undetected Data Exfiltration: As mentioned earlier, file pumping can be used to secretly extract data from a target system. Through subtle manipulations of files, attackers can slowly and quietly exfiltrate valuable data, such as intellectual property, customer records, or confidential corporate data, over extended periods, often without raising suspicion.
  4. Increased Resource Utilization: File pumping can also be used as part of a denial-of-service attack, wherein the file manipulation overwhelms system resources like memory, bandwidth, or disk space. This could lead to slower system performance, increased costs for resource allocation, or even system failure in severe cases.
  5. Reputational Damage: Organizations that are targeted by file pumping attacks, particularly those that result in service interruptions, data breaches, or malware infections, can suffer significant reputational damage. Customers and clients may lose confidence in the ability of the organization to protect their data, which can result in lost business opportunities and long-term brand harm.

Preventing and Mitigating File Pumping Attacks

Mitigating the risks of file pumping requires a combination of preventive strategies and active monitoring. Some best practices include:

  1. File Integrity Checks: Implement file integrity monitoring solutions that track changes to file size, structure, and contents. By identifying unusual modifications or inflations in file size, organizations can identify potential threats early.
  2. Proper File Handling and Validation: Ensure that all systems handling file uploads, downloads, and transfers are properly configured with size limits and security checks to validate the integrity and content of files. This includes rejecting files that exceed size limits or do not conform to expected formats.
  3. Use of Focused Cybersecurity Tools: Deploy advanced cybersecurity tools that inspect the full content of files, including potential hidden payloads or malicious code embedded within otherwise benign files. These systems can analyze files for suspicious patterns and prevent potential exploitation.
  4. Segmentation and Sandboxing: Use network segmentation to limit the damage of an attack and sandboxing techniques to isolate files before they are executed or processed. By preventing files from interacting with critical systems until they are fully inspected, you can reduce the risk of compromise.
  5. Regular Security Audits and Testing: Continuously test and audit systems for vulnerabilities that could be exploited by file manipulation tactics. Penetration testing, vulnerability scanning, and red teaming can help identify weaknesses in the file handling process and the overall security posture of the organization.

Conclusion

File pumping is a form of attack that manipulates files in order to bypass security systems, deploy malicious payloads, or disrupt system operations. By inflating file size, altering file structures, or embedding malicious content, attackers can evade detection and cause serious harm to organizations.

With the increasing complexity of cyberthreats, organizations need to adopt proactive security measures, such as file integrity monitoring, sandboxing, and robust cybersecurity tools, to defend against these types of attacks and ensure the integrity and availability of their critical systems and data.

About BlackFog

BlackFog is the leader in on-device data privacy, data security and ransomware prevention. Our behavioral analysis and anti data exfiltration (ADX) technology stops hackers before they even get started. Our cyberthreat prevention software prevents ransomware, spyware, malware, phishing, unauthorized data collection and profiling and mitigates the risks associated with data breaches and insider threats. BlackFog blocks threats across mobile and desktop endpoints, protecting organizations data and privacy, and strengthening regulatory compliance.