CVE-2016-3861 in Android
Summary
by MITRE
LibUtils in Android 4.x before 4.4.4, 5.0.x before 5.0.2, 5.1.x before 5.1.1, 6.x before 2016-09-01, and 7.0 before 2016-09-01 mishandles conversions between Unicode character encodings with different encoding widths, which allows remote attackers to execute arbitrary code or cause a denial of service (heap-based buffer overflow) via a crafted file, aka internal bug 29250543.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 08/25/2025
The vulnerability identified as CVE-2016-3861 resides within the LibUtils component of Android operating systems, affecting versions spanning from Android 4.x through 7.0 before specific security patches were released. This flaw represents a critical heap-based buffer overflow condition that manifests during Unicode character encoding conversions, specifically when handling different encoding widths between various character encodings. The vulnerability stems from improper memory management during the conversion process, where the system fails to adequately validate or bound-check the output buffer when translating between Unicode encodings with varying bit widths. This issue creates a scenario where maliciously crafted input files can trigger memory corruption that adversaries can exploit for arbitrary code execution or system denial of service.
The technical root cause of this vulnerability aligns with CWE-121, heap-based buffer overflow, and demonstrates characteristics consistent with CWE-704, improper encoding handling, where the system's Unicode processing logic does not properly account for the differences in encoding widths between source and target character sets. The flaw operates by processing input files that contain specially crafted Unicode sequences, where the conversion logic assumes fixed buffer sizes or fails to account for the potential expansion of character data during encoding transitions. When the system encounters these malformed sequences, it allocates insufficient memory for the converted output, leading to buffer overflows that can be leveraged to overwrite adjacent memory regions. This memory corruption typically occurs in heap memory structures managed by the LibUtils library, making it particularly dangerous as it can be triggered during routine file processing operations.
The operational impact of CVE-2016-3861 extends beyond simple denial of service to encompass full arbitrary code execution capabilities, representing a severe security risk for affected Android devices. Attackers can exploit this vulnerability remotely through malicious files delivered via email attachments, web downloads, or file sharing platforms, making it particularly dangerous in mobile environments where users frequently interact with untrusted content. The vulnerability affects the core system libraries that handle file processing, making it difficult to contain and potentially allowing attackers to gain elevated privileges or access sensitive system resources. The attack surface includes any application or system function that relies on LibUtils for file processing, particularly those handling text content, configuration files, or user-generated content that might contain Unicode characters. This vulnerability was particularly concerning given its potential to be exploited in the context of mobile malware campaigns, where attackers could leverage the arbitrary code execution capability to install persistent backdoors or exfiltrate device data.
Mitigation strategies for CVE-2016-3861 require immediate deployment of security patches provided by Google and device manufacturers, as the vulnerability represents an exploitable condition that can be leveraged by remote attackers without user interaction. Organizations should prioritize updating all affected Android devices to versions containing the patched LibUtils implementation, specifically targeting Android 4.4.4, 5.0.2, 5.1.1, and 2016-09-01 release versions for Android 6.x and 7.0. System administrators should implement network-based filtering to prevent the delivery of potentially malicious files containing the vulnerable Unicode sequences, while also monitoring for suspicious file processing activities that might indicate exploitation attempts. The vulnerability demonstrates the importance of proper input validation and memory management in system libraries, particularly those handling character encoding conversions. Security professionals should also consider implementing application whitelisting policies and sandboxing mechanisms to limit the potential impact of exploitation attempts, as the vulnerability affects core system functionality that is difficult to isolate completely. The ATT&CK framework categorizes this vulnerability under T1059, Command and Scripting Interpreter, as exploitation typically involves executing malicious code through the compromised system processes, and T1203, Exploitation for Client Execution, which describes how attackers can leverage system vulnerabilities to execute code on target devices.