Navigating Advanced Cybersecurity Risks: The Perils of Microsoft Office Files in SAP Applications

In today's digitally driven corporate environments, SAP applications stand as colossal pillars supporting myriad business processes, from procurement and supply chain management to human resources and customer relationship management.

However, the integration of Microsoft Office files into these SAP ecosystems has unwittingly opened a Pandora’s box of cybersecurity vulnerabilities. And cyber-criminals, with their ever-evolving tactics, have leveraged these vulnerabilities to launch sophisticated attacks.

This post aims to shed light on the critical attack vectors associated with Microsoft Office documents within SAP applications and outline effective mitigation strategies to safeguard your digital crown-jewels.

How Microsoft Office Files Can Be an Attack Vector in SAP Environments

To implement effective mitigation and protection strategies, it's essential to dissect the underlying mechanisms and exploit techniques of the attack vectors associated with Microsoft Office files in SAP environments.

Let's delve into the specifics, providing a granular view of how these attacks are constructed and executed.

Macro-based Malware

One of the most traditional yet potent threats, macro-based malware, involves embedding malicious VBA scripts within Office documents. When unsuspecting users enable macros, the malware is executed, potentially leading to data breaches or system compromise.

Macro-based malware often employs sophisticated obfuscation techniques to bypass static analysis and evade antivirus detection. For example, attackers use string splitting and concatenation to disguise malicious functions.

Attackers also leverage document properties or environment variables as a decryption key for encrypted payloads within the macro, executing the payload only when the document is opened in the target environment. This technique, known as "environmental keying," ensures that the payload remains dormant and undetected during analysis.

Embedded OLE Objects

Object Linking and Embedding (OLE) allows embedding and linking to documents and other objects. Cybercriminals exploit this feature by embedding malicious objects in Office files, which, when accessed within SAP applications, can execute harmful code.

OLE objects within Office documents use the Compound File Binary Format (CFBF), which is essentially a file system within a file, allowing for the storage of embedded objects.

Attackers exploit this complexity by embedding malicious executable files or scripts camouflaged as benign objects. For instance, an attacker could embed a malicious `.sct` (Windows Script Component) file within an Excel document. The file would appear as a harmless chart or image but, when activated, executes a script that could perform actions like downloading additional payloads from a C&C (Command and Control) server.

Dynamic Data Exchange (DDE) Attacks

Dynamic Data Exchange (DDE) is an interprocess communication protocol used by Microsoft Windows and Office applications to share data between applications in real time.

While initially designed for legitimate purposes such as automating data transfer between applications, DDE presents a significant security risk when abused by malicious actors.

Exploitation Techniques and Examples:

Command Execution via Excel Spreadsheets

Attackers embed malicious DDE fields in Excel spreadsheets, enticing users to open the document and enable content updates. Upon acceptance, the embedded DDE commands execute, allowing attackers to execute arbitrary commands, download malware, or steal sensitive data from the victim's system, for example from an SAP application the user’s Office has access to.

Payload Delivery via Word Documents

Malicious Word documents may contain embedded DDE fields that execute commands to download and execute malware from remote servers. By leveraging the trust associated with Office documents, attackers can deceive users into executing malicious commands, leading to system compromise or data exfiltration.

Remote Template Injection

Office Open XML (OOXML) documents (.docx, .xlsx, .pptx) are structured as ZIP archives containing XML files and other resources.

Remote template injection exploits the relationships (defined in `.rels` files) between document parts. An attacker can modify a document's `.rels` file to change the target of a template relationship to a URL under their control. When the document is opened, Office applications attempt to load the template from this URL, executing any malicious code contained within the template.

Phishing Links within Documents: Utilizing Field Codes for Stealth

This vector involves embedding hyperlinks to malicious websites within Office documents. These links are often disguised as legitimate resources or calls to action. Unsuspecting users clicking on these links are directed to phishing sites designed to steal sensitive information. Such a phishing site could mimic the look of the victim’s organizations FIORI Launchpad login. Phishing attacks within Office documents can be made more sophisticated by using field codes, which are instructions that command Word to insert automatic data into a document. By manipulating field codes, an attacker can embed a malicious URL in a way that is not visible in the document's text, but redirects users when clicked. For example, the field code `{ HYPERLINK "http://legitimate-site.com" \t "http://malicious-site.com" }` can display a legitimate URL to the user but redirect them to a malicious site when clicked.

Zero-day Vulnerabilities: Buffer Overflows and Arbitrary Code Execution

Zero-day vulnerabilities are previously unknown software flaws that can be exploited by attackers before developers have an opportunity to issue a fix.

Exploiting zero-day vulnerabilities in Office applications often involves intricate techniques like buffer overflows, heap spraying, or use-after-free vulnerabilities. For instance, a maliciously crafted document might contain a malformed image or object designed to overflow a buffer within the Office application, corrupting memory in a way that allows the attacker to inject and execute arbitrary code.

These exploits are highly sophisticated and require a deep understanding of both the application's code and the target operating system's memory management.

Mitigation Strategies

• Patch, patch, patch! The best mitigation against vulnerability exploits is to deploy patches to any component, any application or endpoint handling Office files in a timely manner. While zero-day vulnerabilities do exist, most threat actors will bet on organizations not deploying patches immediately, leaving the attacker with an attack window during which they can exploit known vulnerabilities on any system that was not yet patched.
• Trust nobody! Given the prevalence of attacks leveraging Office documents, no such document should be processed by an SAP application before being scanned for threats. Recent SAP kernels will even warn admins in the SAP Security Audit Log if a file transferred to the application was not scanned via the SAP VSI (Virus Scan Interface) before processing (SAL Event FU9).
• Analyze the applications requirements with great scrutiny to determine if high-risk content, such as macros, OLE or DDE can be blocked with little or reasonable impact to the business process. SAP’s VSI allows admins to block active content. bowbridge Anti-Virus for SAP Solutions overlays this switch with granular definitions of what should constitute active content, allowing admins to implement policies that carefully balance mission-critical business needs versus security requirements.

While Office documents can increase the cybersecurity risk to your mission-critical SAP systems, there is still much you can do: Being aware of the risks and mitigating them can make a significant difference.