CVE-2018-6088 in Chrome
Summary
by MITRE
An iterator-invalidation bug in PDFium in Google Chrome prior to 66.0.3359.106 allowed a remote attacker to execute arbitrary code inside a sandbox via a crafted PDF file.
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Analysis
by VulDB Data Team • 06/12/2023
The vulnerability identified as CVE-2018-6088 represents a critical iterator-invalidation flaw within PDFium, the PDF rendering engine used by Google Chrome and other applications. This defect exists in the way PDFium handles memory management during PDF document processing, specifically when iterating through data structures that contain embedded objects within PDF files. The vulnerability manifests when a malicious PDF file contains carefully crafted objects that trigger improper iterator invalidation during document parsing, creating a condition where memory access occurs after an iterator has been invalidated. This type of bug falls under the category of memory safety issues and is particularly dangerous because it can be exploited remotely without user interaction, making it a prime target for zero-day attacks.
The technical exploitation of this vulnerability occurs when a remote attacker crafts a PDF file that triggers a specific sequence of operations within PDFium's object processing pipeline. During normal PDF parsing, the engine maintains iterators to traverse through various object types and their associated data structures. When a malicious PDF contains objects that cause these iterators to become invalid while still being referenced, the system attempts to access memory locations that may have been freed or reallocated. This iterator-invalidation condition leads to memory corruption that can be leveraged to execute arbitrary code within the sandboxed environment of Chrome's renderer process. The flaw is particularly insidious because it operates within the confines of the browser's security model, allowing attackers to bypass traditional sandbox boundaries and escalate privileges. According to CWE-122, this vulnerability maps to memory corruption issues that arise from improper handling of iterator invalidation, while the ATT&CK framework categorizes this as a code injection technique under T1059.007, specifically targeting browser-based applications through memory corruption exploits.
The operational impact of CVE-2018-6088 extends far beyond simple code execution, as it represents a complete bypass of Chrome's security architecture. When successfully exploited, the vulnerability allows attackers to execute arbitrary code with the privileges of the Chrome sandbox, which typically operates with restricted permissions but still provides access to system resources. This enables threat actors to perform actions such as reading sensitive files, modifying system settings, or installing malware without user consent. The vulnerability affects all versions of Google Chrome prior to 66.0.3359.106, making it particularly dangerous as it impacts a significant portion of users who may not have updated their browsers. Organizations relying on Chrome for web browsing face severe risks, as the exploit can be delivered through standard web traffic without requiring any special user interaction, making it ideal for mass deployment attacks. The sandbox escape capability means that even if the initial attack vector is blocked, the vulnerability can still provide a persistent foothold for attackers to escalate their access and maintain long-term presence within target networks.
Mitigation strategies for CVE-2018-6088 center exclusively on immediate browser updates to version 66.0.3359.106 or later, which contains the necessary patches to address the iterator-invalidation issue in PDFium. Organizations should implement comprehensive patch management procedures to ensure all Chrome installations are updated promptly, as the vulnerability affects both desktop and mobile versions of the browser. Security teams should also consider implementing additional network-level protections such as web application firewalls that can detect and block suspicious PDF content, though these measures are not foolproof given the remote nature of the attack. Browser hardening techniques including disabling PDF rendering in Chrome, using alternative PDF viewers, or implementing strict content security policies can provide additional layers of defense. The vulnerability highlights the importance of maintaining up-to-date software, as the patch for this issue was released as part of Chrome's regular security updates. Organizations should also consider implementing monitoring for unusual browser behavior or memory access patterns that might indicate exploitation attempts, though such detection is challenging given the sophisticated nature of the attack. According to industry best practices, regular security assessments and penetration testing of browser-based applications should include evaluation of PDF rendering engines for similar memory safety issues that could lead to similar exploitation vectors.