CVE-2016-1685 in Chrome
Summary
by MITRE
core/fxge/ge/fx_ge_text.cpp in PDFium, as used in Google Chrome before 51.0.2704.63, miscalculates certain index values, which allows remote attackers to cause a denial of service (out-of-bounds read) via a crafted PDF document.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 12/20/2018
The vulnerability identified as CVE-2016-1685 resides within the PDFium library's text rendering component, specifically in the core/fxge/ge/fx_ge_text.cpp file. This flaw manifests as an improper index calculation mechanism that fails to validate array boundaries during text processing operations. The vulnerability affects Google Chrome versions prior to 51.0.2704.63, making it a significant concern for users running outdated browser versions. PDFium serves as the core PDF rendering engine for Chrome and other applications, making this vulnerability particularly dangerous as it can be exploited through malicious PDF documents delivered via web pages or email attachments.
The technical nature of this vulnerability stems from a classic out-of-bounds read condition where the PDFium library does not properly validate index values when processing text elements within PDF documents. When a crafted PDF contains malformed text data, the library's text rendering code attempts to access memory locations beyond the allocated array boundaries, resulting in an out-of-bounds read operation. This miscalculation occurs during the processing of font metrics and text positioning calculations, where the system fails to properly validate the range of indices used to access text-related data structures. The flaw represents a direct violation of proper input validation principles and can be classified under CWE-129 as an insufficient input validation leading to out-of-bounds access.
From an operational perspective, this vulnerability enables remote attackers to execute a denial of service attack by crafting specially designed PDF documents that trigger the out-of-bounds read condition. When a victim's browser loads such a malicious PDF, the PDFium library crashes or becomes unstable, leading to complete browser termination or rendering failure. The attack vector is particularly concerning because it requires no user interaction beyond visiting a web page containing the malicious PDF or opening an email attachment with a crafted PDF file. This vulnerability falls under the ATT&CK technique T1203 - Exploitation for Client Execution, as it leverages a client-side application vulnerability to execute arbitrary code or cause service disruption. The impact extends beyond simple browser crashes, as the instability can potentially be exploited to execute arbitrary code or escalate privileges depending on the system configuration and browser sandboxing mechanisms.
The mitigation strategy for CVE-2016-1685 primarily involves updating to Google Chrome version 51.0.2704.63 or later, which contains the patched PDFium library implementation. Organizations should prioritize patching this vulnerability across all affected systems, particularly those running older Chrome versions or applications that rely on the vulnerable PDFium library. Additional protective measures include implementing web application firewalls to filter suspicious PDF content, deploying sandboxing mechanisms to limit the impact of potential exploitation, and educating users about the risks of opening untrusted PDF documents. The vulnerability demonstrates the critical importance of proper input validation and boundary checking in security-critical components, as highlighted by CWE-707 and the broader category of memory safety issues that affect modern software systems. Regular security audits and automated vulnerability scanning should be implemented to identify similar issues in other components of the PDF rendering pipeline and prevent similar vulnerabilities from being introduced in future code releases.