CVE-2016-0935 in Acrobat Reader
Summary
by MITRE
Double free vulnerability in Adobe Reader and Acrobat before 11.0.14, Acrobat and Acrobat Reader DC Classic before 15.006.30119, and Acrobat and Acrobat Reader DC Continuous before 15.010.20056 on Windows and OS X allows attackers to execute arbitrary code via a crafted ExtGState dictionary.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 07/03/2022
The vulnerability identified as CVE-2016-0935 represents a critical double free flaw in Adobe Reader and Acrobat products across multiple versions, specifically affecting Windows and macOS operating systems. This vulnerability resides within the handling of ExtGState dictionaries in PDF processing, which are used to define graphical state parameters for rendering PDF content. The double free condition occurs when the application attempts to free the same memory block twice during the processing of maliciously crafted PDF files, creating a scenario where attackers can manipulate memory corruption to achieve arbitrary code execution.
The technical implementation of this vulnerability stems from improper memory management within Adobe's PDF parsing engine, where the ExtGState dictionary processing routine fails to properly track memory allocations and deallocations. When a crafted PDF file contains maliciously constructed ExtGState entries, the application's memory management subsystem executes a free operation on the same memory address twice, leading to heap corruption that can be exploited by adversaries. This flaw operates at the intersection of memory safety issues and code execution vulnerabilities, with the double free condition creating a predictable memory layout that attackers can manipulate through carefully crafted input data structures.
From an operational perspective, this vulnerability presents a significant risk to organizations relying on Adobe Reader and Acrobat for document processing, as it allows remote code execution without user interaction. The attack vector requires only that a user opens a malicious PDF file, making it particularly dangerous for email-based attacks and web-based exploitation. The vulnerability's impact extends beyond individual user systems to enterprise environments where PDF documents are frequently exchanged, potentially enabling attackers to establish persistent access, escalate privileges, or deploy additional malicious payloads. This aligns with ATT&CK technique T1059.007 for command and script interpreter and T1203 for Exploitation for Client Execution, both of which describe methods for executing malicious code through document-based attacks.
The exploitation of this vulnerability requires attackers to construct a PDF file containing specially crafted ExtGState dictionaries that trigger the double free condition during memory deallocation. The flaw's classification as a heap-based memory corruption vulnerability places it within CWE-415, which describes improper double free conditions in memory management. Security researchers have noted that the vulnerability's exploitability is enhanced by the predictable nature of memory corruption patterns that result from double free operations, making it more accessible to attackers with intermediate skill levels. Organizations should consider implementing network-based protections such as PDF sandboxing and content filtering, while also ensuring that all systems are updated to patched versions of Adobe Reader and Acrobat to prevent exploitation of this vulnerability. The remediation process requires immediate patch deployment across all affected systems, as the vulnerability does not require user interaction to be exploited, making it particularly dangerous for unpatched environments.