CVE-2021-38571 in Foxit
Summary
by MITRE • 08/12/2021
An issue was discovered in Foxit Reader and PhantomPDF before 10.1.4. It allows DLL hijacking, aka CNVD-C-2021-68000 and CNVD-C-2021-68502.
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Analysis
by VulDB Data Team • 08/16/2021
The vulnerability identified as CVE-2021-38571 represents a critical DLL hijacking flaw affecting Foxit Reader and PhantomPDF versions prior to 10.1.4. This security weakness stems from improper dynamic link library loading mechanisms within the affected software applications, creating opportunities for malicious actors to execute arbitrary code on targeted systems. The vulnerability has been independently identified and catalogued under multiple Chinese vulnerability databases including CNVD-C-2021-68000 and CNVD-C-2021-68502, highlighting its significance in the security landscape. The flaw specifically manifests when the applications attempt to load dynamic link libraries without properly validating or restricting the search paths, allowing attackers to place malicious DLL files in locations where the legitimate libraries would normally be loaded.
The technical implementation of this vulnerability involves the exploitation of insecure library loading practices that violate established security principles. When Foxit Reader or PhantomPDF launches, they traverse a predetermined search path to locate required DLL files. If an attacker can place a malicious DLL with the same name as a legitimate library in a directory that appears earlier in the search order, the system will load the malicious code instead of the intended library. This behavior directly aligns with CWE-426 Untrusted Search Path vulnerabilities, where applications fail to properly validate library locations. The attack vector typically involves placing the malicious DLL in the same directory as the vulnerable application or in a directory that appears before system directories in the search path, effectively bypassing normal security controls.
The operational impact of this vulnerability extends beyond simple privilege escalation or code execution, as it provides attackers with a persistent foothold within targeted environments. Successful exploitation allows adversaries to execute arbitrary commands with the privileges of the affected application, potentially leading to complete system compromise. In enterprise environments where these applications are commonly used for document processing, the implications are particularly severe as attackers could leverage this vulnerability to access sensitive corporate documents or establish backdoors for extended access. The vulnerability also aligns with ATT&CK technique T1574.001 Dynamic Linker Hijacking, which describes methods for gaining code execution through manipulation of dynamic link library loading processes. Organizations using these applications face heightened risk during routine document handling activities, as simply opening a maliciously crafted document could trigger the exploitation chain.
Mitigation strategies for CVE-2021-38571 should prioritize immediate application updates to version 10.1.4 or later, where Foxit has implemented proper DLL loading security measures. System administrators should also implement application whitelisting policies to restrict which DLLs can be loaded by the vulnerable applications. Additional protective measures include modifying the system PATH environment variable to ensure that system directories are prioritized over user directories in library search paths. Security monitoring should be enhanced to detect unusual DLL loading patterns or attempts to place files in application directories. Organizations should also consider implementing least privilege principles for user accounts that interact with these applications, limiting the potential damage from successful exploitation. The vulnerability demonstrates the critical importance of secure coding practices and proper library loading mechanisms, as highlighted in industry standards that emphasize the need for applications to validate and restrict dynamic library loading to prevent such attacks from succeeding.