CVE-2018-9521 in Android
Summary
by MITRE
In parseMPEGCCData of NuPlayer2CCDecoder.cpp, there is a possible out of bounds write due to an incorrect bounds check. This could lead to remote code execution in an unprivileged process with no additional execution privileges needed. User interaction is needed for exploitation. Product: Android. Versions: Android-9. Android ID: A-111874331
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Analysis
by VulDB Data Team • 04/13/2020
The vulnerability identified as CVE-2018-9521 represents a critical out-of-bounds write flaw within the Android multimedia processing subsystem. This issue exists in the NuPlayer2CCDecoder.cpp file where the parseMPEGCCData function performs an incorrect bounds check during the parsing of closed caption data. The flaw manifests when the system processes MPEG-2 closed caption data, which is commonly used in broadcast television content and streaming media applications. The vulnerability falls under the Common Weakness Enumeration category of CWE-129, specifically addressing improper validation of array index values that leads to out-of-bounds memory access.
The technical implementation of this vulnerability allows for remote code execution through a carefully crafted media file or stream that triggers the malformed closed caption data parsing. When an Android device processes such content, the incorrect bounds check permits writing data beyond the allocated memory buffer, potentially overwriting adjacent memory locations including function pointers, return addresses, or other critical program state information. This memory corruption can be exploited to redirect execution flow and ultimately achieve code execution within the context of the unprivileged media processing service. The attack vector requires user interaction to trigger the malicious media content, typically through downloading or streaming media files that contain the crafted closed caption data.
The operational impact of CVE-2018-9521 is significant as it affects Android 9.0 and potentially earlier versions, representing a substantial attack surface across numerous mobile devices. The vulnerability's exploitation does not require elevated privileges, making it particularly dangerous as it can be leveraged by malicious actors to compromise devices through seemingly benign media consumption activities. The attack chain typically involves delivering malicious media content through various channels such as email attachments, web downloads, or streaming services, where users inadvertently trigger the vulnerable parsing code. This vulnerability directly maps to ATT&CK technique T1059.007 for command and scripting interpreter, specifically through the use of media processing as a vector for code execution, and T1203 for exploitation for privilege escalation.
Mitigation strategies for this vulnerability include applying the latest security patches from Google, which address the bounds checking implementation in the NuPlayer2 component. System administrators should prioritize updating affected Android devices to versions that contain the fixed implementation of the parseMPEGCCData function with proper bounds validation. Additionally, network-level filtering can be implemented to restrict access to potentially malicious media content, though this approach is less effective as the vulnerability can be triggered through various legitimate media sources. Device manufacturers should also consider implementing additional sandboxing measures around media processing components and enabling automatic security updates to minimize exposure windows. The vulnerability highlights the importance of robust input validation in multimedia processing libraries and serves as a reminder of the security implications inherent in complex media parsing systems that handle untrusted data from external sources.