CVE-2021-21219 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-2021-21219 represents a critical information disclosure flaw within PDFium, the PDF rendering library employed by Google Chrome and numerous other applications. This issue stems from the improper initialization of memory structures during PDF processing operations, creating a pathway for remote attackers to extract sensitive data from application memory. The vulnerability affects Chrome versions prior to 90.0.4430.72, making it particularly concerning given the widespread use of Chrome as a primary web browser across enterprise and consumer environments. The flaw demonstrates how seemingly minor memory management issues can have significant security implications when exploited in the context of web-based attacks.
The technical root cause of this vulnerability lies in the handling of uninitialized data within PDFium's memory allocation and processing routines. When Chrome processes maliciously crafted PDF files, the library fails to properly initialize certain memory regions before using them, potentially exposing previously allocated memory contents that may contain sensitive information such as cryptographic keys, user credentials, session tokens, or other confidential data. This type of vulnerability falls under the CWE-457 category of "Use of Uninitialized Variable" and represents a classic example of how improper memory management can create information leakage channels. The flaw operates at the application layer, specifically targeting the PDF rendering engine's memory handling mechanisms rather than lower-level system vulnerabilities.
From an operational perspective, this vulnerability enables remote attackers to conduct information disclosure attacks without requiring user interaction beyond visiting a malicious website hosting the crafted PDF file. The attack vector is particularly dangerous because it can be delivered through standard web browsing activities, making it difficult to detect and prevent through traditional network monitoring approaches. Attackers can potentially extract sensitive information from the victim's browser process memory, including but not limited to authentication tokens, personal data, or other confidential information that may have been present in memory at the time of processing. The impact extends beyond individual users to potentially compromise enterprise security if attackers can leverage this information to gain further access to protected systems or data repositories.
The mitigation strategy for CVE-2021-21219 primarily involves updating to Google Chrome version 90.0.4430.72 or later, which includes patches that properly initialize memory structures within PDFium. Organizations should prioritize this update across all affected systems, particularly those running older Chrome versions or using Chrome-based applications that may be vulnerable. Security teams should also implement network monitoring to detect potential exploitation attempts through malicious PDF content and consider deploying web application firewalls or content filtering solutions that can block suspicious PDF files. Additionally, users should be educated about the risks of visiting untrusted websites and opening unexpected PDF attachments. This vulnerability aligns with ATT&CK technique T1566.001 for "Phishing: Spearphishing Attachment" and demonstrates the importance of maintaining up-to-date software to prevent exploitation of known vulnerabilities. The remediation process should include thorough testing of updated versions to ensure compatibility with existing workflows while addressing the memory initialization issues that enabled this information disclosure attack.