CVE-2021-21217 in Chrome
Summary
by MITRE • 04/26/2021
Uninitialized data in PDFium in Google Chrome prior to 90.0.4430.72 allowed a remote attacker to obtain potentially sensitive information from process memory via a crafted PDF file.
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Analysis
by VulDB Data Team • 04/30/2021
The vulnerability identified as CVE-2021-21217 represents a critical security flaw within PDFium, the PDF rendering library that powers Google Chrome's document handling capabilities. This issue stems from improper initialization of memory structures during PDF processing operations, creating a pathway for remote attackers to extract sensitive data from the application's memory space. The vulnerability affects Chrome versions prior to 90.0.4430.72, making it a significant concern for users who have not yet updated their browsers. The flaw manifests when the PDFium component processes maliciously crafted PDF files that contain uninitialized data structures, which can subsequently be read by an attacker through memory inspection techniques.
The technical root cause of this vulnerability lies in the improper handling of uninitialized memory within PDFium's parsing and rendering functions. When Chrome encounters a PDF file containing specific malformed data structures, the PDFium library fails to properly initialize certain memory regions before utilizing them. This creates a scenario where residual data from previous operations or memory allocation patterns may remain in these uninitialized areas, effectively leaking information that could include sensitive context such as cryptographic keys, user credentials, session tokens, or other confidential data. The vulnerability falls under CWE-457, which specifically addresses the use of uninitialized variables, making it a classic example of memory safety issues in software development. The flaw operates at the intersection of memory management and input validation, where insufficient sanitization of parsed PDF elements leads to information disclosure.
The operational impact of CVE-2021-21217 extends beyond simple information leakage, as it creates potential vectors for more sophisticated attacks within the broader threat landscape. Remote attackers can leverage this vulnerability to conduct reconnaissance activities, gathering intelligence about running processes and system configurations that could inform subsequent attacks. The vulnerability aligns with ATT&CK technique T1005, which focuses on data from local systems, and T1059, which involves command and script interpreters, as the leaked information could be used to craft more targeted attacks. The threat model suggests that attackers could use this information to perform privilege escalation attempts, identify system vulnerabilities, or develop more advanced exploit chains that build upon the initial information disclosure. Organizations running outdated Chrome versions face increased risk of targeted attacks, particularly in environments where sensitive data is frequently processed through web browsers.
Mitigation strategies for CVE-2021-21217 primarily center on immediate browser updates to versions 90.0.4430.72 or later, where Google has implemented proper memory initialization routines within PDFium. System administrators should prioritize patch management protocols to ensure all user endpoints are updated promptly, as this vulnerability can be exploited through standard web browsing activities without user interaction. Additional protective measures include implementing web application firewalls that can detect and block suspicious PDF file patterns, deploying sandboxing mechanisms that limit the potential impact of exploitation, and establishing monitoring systems to detect anomalous memory access patterns. The vulnerability also underscores the importance of comprehensive input validation and memory safety practices in software development, particularly for components that handle untrusted data such as PDF files. Organizations should consider implementing automated scanning tools that can identify and remediate similar issues in their own software applications, following the principle of least privilege and defense in depth to minimize the attack surface.