CVE-2021-21218 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-2021-21218 represents a critical information disclosure flaw within PDFium, the embedded PDF rendering library used by Google Chrome and other applications. This vulnerability stems from the improper handling of uninitialized data during PDF processing operations, creating a potential pathway for remote attackers to extract sensitive information from process memory. The issue affects Chrome versions prior to 90.0.4430.72, making it a significant concern for users running outdated browser versions. The flaw specifically manifests when the PDFium library processes crafted PDF files that contain uninitialized memory regions, allowing attackers to potentially access data that should remain confidential.
The technical implementation of this vulnerability involves PDFium's memory management during the parsing and rendering of PDF documents. When processing certain malformed PDF structures, the library fails to properly initialize memory segments before using them, resulting in the exposure of previously allocated memory contents. This includes potentially sensitive data such as cryptographic keys, user credentials, session tokens, or other confidential information that may have resided in the memory space at the time of the uninitialized access. The vulnerability operates at the intersection of memory safety and information disclosure, where improper initialization creates a window for data leakage that can be exploited remotely without user interaction. This type of vulnerability is classified under CWE-457 as "Use of Uninitialized Variable" and falls within the broader category of information disclosure vulnerabilities that can lead to privilege escalation or data breaches.
The operational impact of CVE-2021-21218 extends beyond simple information disclosure, as the potential for sensitive data extraction creates multiple attack vectors for threat actors. Remote attackers can craft malicious PDF files that, when opened by an affected browser, trigger the uninitialized memory access pattern and subsequently extract process memory contents. This vulnerability is particularly concerning in environments where users frequently encounter PDF documents from untrusted sources, including email attachments, web downloads, or document sharing platforms. The attack requires no user interaction beyond opening the malicious document, making it a significant threat vector in phishing campaigns or targeted attacks. Security researchers have categorized this vulnerability under the ATT&CK framework as part of the "T1059 - Command and Scripting Interpreter" and "T1566 - Phishing" techniques, where attackers leverage PDF-based delivery mechanisms to establish initial access and subsequently extract sensitive information from compromised systems.
Mitigation strategies for CVE-2021-21218 primarily focus on immediate browser updates to versions 90.0.4430.72 or later, which contain the necessary patches to address the uninitialized memory handling issue. Organizations should implement comprehensive patch management procedures to ensure all Chrome installations are updated promptly, particularly in enterprise environments where multiple users may be exposed to untrusted PDF content. Network security controls such as PDF content filtering and sandboxing mechanisms can provide additional defense layers, though these should not be considered substitutes for proper patching. Security monitoring should include detection of suspicious PDF file handling activities and memory access patterns that could indicate exploitation attempts. The vulnerability highlights the importance of memory safety practices in widely-used software libraries and underscores the need for regular security audits of core components like PDF rendering engines. System administrators should also consider implementing user education programs to raise awareness about the risks of opening PDF files from untrusted sources, as social engineering remains a critical component in successful exploitation of such vulnerabilities.