CVE-2015-6756 in Chrome
Summary
by MITRE
Use-after-free vulnerability in the CPDFSDK_PageView implementation in fpdfsdk/src/fsdk_mgr.cpp in PDFium, as used in Google Chrome before 46.0.2490.71, allows remote attackers to cause a denial of service (heap memory corruption) or possibly have unspecified other impact by leveraging mishandling of a focused annotation in a PDF document.
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Analysis
by VulDB Data Team • 06/21/2022
The CVE-2015-6756 vulnerability represents a critical use-after-free flaw within the PDFium library's CPDFSDK_PageView implementation, specifically in the fpdfsdk/src/fsdk_mgr.cpp file. This vulnerability affects Google Chrome versions prior to 46.0.2490.71 and demonstrates how improper memory management in PDF rendering components can lead to severe security implications. The flaw occurs when the PDFium library handles focused annotations within PDF documents, creating a scenario where memory previously allocated to an object is accessed after it has been freed, potentially leading to unpredictable behavior and system instability. This type of vulnerability falls under the CWE-416 category, which specifically addresses the use of freed memory, making it a prime example of improper memory management that can be exploited by malicious actors.
The technical exploitation of this vulnerability involves crafting a malicious PDF document that contains specially formatted annotations which trigger the flawed memory handling logic within the CPDFSDK_PageView component. When a user opens such a document in an affected version of Chrome, the PDFium library processes the focused annotation and subsequently attempts to access memory that has already been deallocated during the normal object lifecycle. This memory corruption can manifest as heap corruption, causing the browser to crash or potentially allowing more sophisticated attacks to exploit the unstable memory state. The vulnerability's impact extends beyond simple denial of service as the use-after-free condition could potentially be leveraged for remote code execution depending on the specific memory layout and exploitation conditions present during the heap corruption event.
From an operational perspective, this vulnerability creates significant risk for organizations relying on older Chrome versions, as it represents a remote attack vector that requires no user interaction beyond opening a malicious PDF document. The exploitation scenario typically involves social engineering tactics where attackers distribute PDF files containing the malicious annotation structures through phishing campaigns, malicious websites, or compromised documents. Security analysts should note that this vulnerability aligns with ATT&CK technique T1203, which involves gaining access to systems through the exploitation of vulnerabilities in software applications, and T1059 which covers the use of command and control channels through compromised applications. The vulnerability's presence in the core PDF rendering engine makes it particularly dangerous as it affects all PDF documents processed by the affected browser version, regardless of their source or content legitimacy.
Mitigation strategies for CVE-2015-6756 primarily focus on immediate patching of affected Chrome versions to ensure users are running at least version 46.0.2490.71 or later, which contains the necessary fixes for the memory management issues in the CPDFSDK_PageView implementation. Organizations should also implement additional security measures such as PDF content filtering, sandboxing mechanisms, and network-based intrusion detection systems that can identify and block suspicious PDF file patterns. Security teams should consider deploying browser hardening measures including disabling unnecessary PDF features, implementing strict content security policies, and monitoring for abnormal memory access patterns. The vulnerability highlights the importance of keeping PDF rendering libraries up to date and demonstrates how even seemingly benign document processing features can become attack vectors when memory safety issues are present in the underlying implementation. Additionally, organizations should conduct regular vulnerability assessments focusing on third-party library components and ensure comprehensive testing of document processing capabilities to identify similar memory safety issues before they can be exploited in the wild.