CVE-2021-41569 in Intrnet
Summary
by MITRE • 11/19/2021
SAS/Intrnet 9.4 build 1520 and earlier allows Local File Inclusion. The samples library (included by default) in the appstart.sas file, allows end-users of the application to access the sample.webcsf1.sas program, which contains user-controlled macro variables that are passed to the DS2CSF macro. Users can escape the context of the configured user-controllable variable and append additional functions native to the macro but not included as variables within the library. This includes a function that retrieves files from the host OS.
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Analysis
by VulDB Data Team • 11/25/2021
The vulnerability identified as CVE-2021-41569 represents a critical local file inclusion flaw within SAS/Intrnet 9.4 versions through build 1520. This issue stems from the default inclusion of a samples library that is automatically loaded through the appstart.sas configuration file. The vulnerability specifically exploits the interaction between user-controllable macro variables and the DS2CSF macro processing functionality. When end-users access the sample.webcsf1.sas program, they inadvertently expose a path where macro variables become user-controlled inputs that can be manipulated to escape the intended execution context. The flaw manifests through the ability to append native macro functions that were not originally designed as configurable variables within the library but are accessible through the macro processing engine.
The technical exploitation occurs through the manipulation of macro variable contexts within the DS2CSF macro invocation. When user inputs are processed through the sample.webcsf1.sas program, the macro variables can be crafted to bypass normal parameter validation and injection points. This allows attackers to leverage built-in macro functions that provide direct access to the host operating system filesystem. The vulnerability operates at the intersection of macro processing, input validation, and privilege escalation, creating a pathway for unauthorized file access and potential system compromise. The flaw is particularly concerning because it leverages default application components that are enabled without explicit user configuration, making it accessible to any user with access to the application interface.
The operational impact of this vulnerability extends beyond simple file access to potentially enable full system compromise. Attackers can utilize the file retrieval capabilities to extract sensitive configuration files, database credentials, application source code, and other system artifacts. The vulnerability's local nature means that exploitation does not require network exposure or external attack vectors, making it particularly dangerous in environments where the application runs with elevated privileges. This represents a significant security risk for organizations that deploy SAS/Intrnet in enterprise environments, as it could enable data exfiltration, privilege escalation, and potentially serve as a foothold for further attacks. The vulnerability aligns with CWE-22 (Improper Limitation of a Pathname to a Restricted Directory) and CWE-94 (Improper Control of Generation of Code) categories, demonstrating how improper input handling can lead to code execution and file access.
Mitigation strategies for CVE-2021-41569 must address both the immediate vulnerability and the underlying architectural issues that enable it. Organizations should immediately update to SAS/Intrnet 9.4 build 1521 or later, which contains the necessary patches to prevent macro variable injection. System administrators should also implement strict input validation and sanitization for all macro variables within the application environment. The configuration of the appstart.sas file should be reviewed to ensure that default sample libraries are not automatically loaded in production environments. Additionally, implementing principle of least privilege for application users and monitoring for unusual file access patterns can help detect potential exploitation attempts. From an ATT&CK framework perspective, this vulnerability maps to T1059.001 (Command and Scripting Interpreter: PowerShell) and T1566 (Phishing) as attackers may use this vulnerability to escalate privileges and establish persistence. Regular security assessments should include verification that the patched versions are properly implemented and that no legacy sample libraries remain active in the application configuration.