CVE-2016-0840 in Android
Summary
by MITRE
Multiple stack-based buffer underflows in decoder/ih264d_parse_cavlc.c in mediaserver in Android 6.x before 2016-04-01 allow remote attackers to execute arbitrary code or cause a denial of service (memory corruption) via a crafted media file, aka internal bug 26399350.
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Analysis
by VulDB Data Team • 07/12/2022
The vulnerability identified as CVE-2016-0840 represents a critical stack-based buffer underflow flaw within the Android mediaserver component that affects Android 6.x versions prior to the 2016-04-01 security patch release. This vulnerability resides in the decoder/ih264d_parse_cavlc.c file, which handles decoding of H.264 video streams using the Cavlc (Context-Adaptive Variable-Length Coding) parsing algorithm. The flaw specifically manifests when processing crafted media files that contain malformed H.264 video data, creating a dangerous condition where attacker-controlled input can overwrite adjacent memory on the stack. The vulnerability is classified under CWE-121 Stack-based Buffer Overflow, which is a well-known weakness category that directly enables arbitrary code execution or system crashes through memory corruption.
The technical exploitation of this vulnerability occurs during the normal processing of H.264 video streams where the decoder fails to properly validate the size of data structures before copying data into fixed-size stack buffers. When a maliciously crafted media file is processed, the parser does not adequately check bounds on variable-length data fields that should be parsed from the video stream, leading to buffer overflows that can overwrite return addresses, function pointers, and other critical stack memory locations. This allows remote attackers to potentially execute arbitrary code with the privileges of the mediaserver process, which typically runs with system-level privileges on Android devices. The vulnerability is particularly dangerous because it can be triggered through standard media playback scenarios, making it exploitable via email attachments, web downloads, or any media file delivery mechanism.
The operational impact of CVE-2016-0840 extends beyond simple denial of service to encompass full system compromise capabilities, as demonstrated by the internal bug reference 26399350 that indicates the severity level within Google's internal tracking systems. The mediaserver process is a core component that handles multimedia processing across the Android platform, making this vulnerability particularly impactful as it affects a fundamental system service. Attackers could leverage this vulnerability to gain unauthorized access to devices, potentially leading to data theft, persistent backdoor installation, or further exploitation of other system components. The vulnerability affects all Android 6.0 devices running versions prior to the April 2016 security patch, representing a significant window of exposure for millions of devices. According to ATT&CK framework, this vulnerability maps to T1059 Command and Scripting Interpreter and T1068 Exploitation for Privilege Escalation, as it enables remote code execution and privilege escalation through system service manipulation.
Mitigation strategies for CVE-2016-0840 primarily focus on timely patch application, as the vulnerability was addressed through the Android Security Bulletin released in April 2016. Organizations and users should immediately update to Android 6.0.1 or later versions that contain the necessary fixes to prevent the buffer overflow conditions. Additionally, network-level defenses can include media file filtering and sandboxing of media processing components to limit the impact of potential exploitation attempts. Device manufacturers and service providers should implement robust patch management processes to ensure timely deployment of security updates. The vulnerability also highlights the importance of input validation in multimedia decoders and serves as a reminder of the critical need for proper bounds checking in parsing functions, particularly those handling variable-length data formats like video codecs. Security monitoring should include detection of unusual mediaserver behavior and memory corruption patterns that might indicate exploitation attempts.