CVE-2018-9537 in Android
Summary
by MITRE
In CAacDecoder_DecodeFrame of aacdecode.cpp, there is a possible out-of-bounds write due to a missing bounds check. This could lead to remote code execution in the media server with no additional execution privileges needed. User interaction is needed for exploitation. Product: Android. Versions: Android-9. Android ID: A-112891564
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Analysis
by VulDB Data Team • 04/13/2020
The vulnerability identified as CVE-2018-9537 represents a critical out-of-bounds write flaw in the Advanced Audio Coding (AAC) decoder component of Android's media framework. This issue resides within the CAacDecoder_DecodeFrame function located in the aacdecode.cpp source file, where a fundamental bounds checking mechanism has been omitted during the audio frame decoding process. The flaw specifically manifests when processing malformed AAC audio data, creating a scenario where the decoder attempts to write data beyond the allocated memory boundaries of its internal buffers. This memory corruption vulnerability directly violates the principles of secure coding practices and represents a classic example of a buffer overflow condition that can be exploited to gain unauthorized code execution privileges.
The operational impact of this vulnerability extends beyond simple media playback functionality and creates a significant security risk for Android devices running Android 9.0 and earlier versions. The vulnerability enables remote code execution without requiring any additional privileges or user interaction beyond the initial exploitation vector, making it particularly dangerous in scenarios where users might unknowingly encounter malicious audio content. The attack surface is broad as any application or service that processes AAC audio streams could potentially be leveraged for exploitation, including web browsers, media players, and even system-level services that handle audio processing. This vulnerability aligns with CWE-787, which specifically addresses out-of-bounds write conditions, and represents a direct violation of the principle of least privilege as it allows arbitrary code execution within the media server context.
The exploitation of this vulnerability follows a typical attack pattern that aligns with ATT&CK framework techniques for code injection and privilege escalation. An attacker would need to craft a malicious AAC audio file that triggers the specific code path containing the missing bounds check, then deliver this file to a target device through various means such as malicious websites, email attachments, or compromised applications. Once executed, the out-of-bounds write could overwrite critical memory structures, potentially allowing an attacker to inject and execute arbitrary code within the media server process. The lack of additional privilege requirements makes this vulnerability particularly dangerous as it can be exploited by attackers with minimal initial access, and the fact that user interaction is required for exploitation suggests that social engineering or drive-by download techniques could be employed to deliver the malicious payload.
Mitigation strategies for this vulnerability should encompass multiple layers of defense to protect against exploitation attempts. Device manufacturers and system administrators should prioritize immediate deployment of security patches that implement proper bounds checking mechanisms in the AAC decoder component, ensuring that all buffer operations include appropriate validation before memory writes occur. The Android security model should be enhanced to include additional sandboxing measures around media processing components, preventing potential privilege escalation even if exploitation occurs. Network-level protections such as content filtering and sandboxed web browsing environments can help reduce the likelihood of successful exploitation by blocking malicious audio content before it reaches the device. Additionally, implementing runtime monitoring and exploit detection mechanisms can provide early warning capabilities for potential exploitation attempts, while regular security audits of media processing libraries should be conducted to identify and remediate similar vulnerabilities across the entire codebase.