CVE-2019-8772 in macOS
Summary
by MITRE
An issue existed in the handling of links in encrypted PDFs. This issue was addressed by adding a confirmation prompt. This issue is fixed in macOS Catalina 10.15. An attacker may be able to exfiltrate the contents of an encrypted PDF.
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Analysis
by VulDB Data Team • 03/15/2024
The vulnerability identified as CVE-2019-8772 represents a significant security flaw in macOS handling of encrypted PDF documents, specifically concerning hyperlink processing within these protected files. This issue manifests in the improper validation and execution of links embedded within encrypted PDFs, creating a potential vector for unauthorized data exfiltration. The flaw exists at the intersection of document security mechanisms and user interaction protocols, where the system fails to adequately verify the legitimacy of hyperlinks before executing them. The vulnerability is particularly concerning because it operates within the context of encrypted documents, which are typically designed to protect sensitive information from unauthorized access. When users open encrypted PDFs containing malicious links, the system's insufficient validation process allows these links to be processed without proper user confirmation, potentially enabling attackers to execute malicious payloads or establish connections to external servers.
The technical implementation of this vulnerability stems from the insufficient sanitization of hyperlink references within encrypted PDF documents. When a user interacts with a link in an encrypted PDF, the system should validate the link's destination and require explicit user confirmation before proceeding with any network activity or file operations. However, the flaw allows these validation steps to be bypassed, particularly in macOS versions prior to Catalina 10.15. This issue falls under CWE-20, which describes improper input validation, and specifically relates to CWE-79, which addresses cross-site scripting vulnerabilities that can occur through improper handling of user-controllable input. The vulnerability operates at the application level, affecting the PDF rendering engine's security controls and represents a breakdown in the security model that should protect users from potentially malicious content within encrypted documents.
The operational impact of CVE-2019-8772 extends beyond simple data exfiltration to encompass broader security implications for users of encrypted PDF documents. Attackers can exploit this vulnerability by crafting malicious encrypted PDFs containing links that, when opened, automatically initiate data transfer operations to attacker-controlled servers. This capability allows for unauthorized access to potentially sensitive information contained within the encrypted documents, undermining the fundamental security premise that encrypted files provide protection against unauthorized data access. The vulnerability is particularly dangerous in enterprise environments where sensitive documents are frequently shared and stored in encrypted formats, as it provides an indirect method for attackers to bypass encryption protections. The security implications are further amplified by the fact that users may not be aware they are opening potentially malicious documents, as the encryption provides a false sense of security that can lead to complacency in security practices.
The remediation for CVE-2019-8772 involved implementing enhanced confirmation prompts for all hyperlink interactions within encrypted PDF documents, as detailed in the macOS Catalina 10.15 release notes. This fix addresses the core issue by ensuring that users are explicitly prompted before any link execution occurs, regardless of whether the document is encrypted or not. The solution aligns with the ATT&CK framework's mitigation strategies for malicious link execution, specifically targeting techniques that involve user interaction and privilege escalation through document-based attacks. Organizations should prioritize updating to macOS Catalina 10.15 or later versions to address this vulnerability, as the confirmation prompt mechanism provides a robust defense against the exploitation of this flaw. Additionally, security administrators should implement network monitoring to detect unusual outbound connections from systems that may have been compromised through this vulnerability, as the attack vector typically involves establishing network connections to external servers. The fix demonstrates the importance of proper input validation and user confirmation mechanisms in security-critical applications, particularly those handling sensitive encrypted data.