CVE-2018-20197 in Freeware Advanced Audio Decoder
Summary
by MITRE
There is a stack-based buffer underflow in the third instance of the calculate_gain function in libfaad/sbr_hfadj.c in Freeware Advanced Audio Decoder 2 (FAAD2) 2.8.8. A crafted input will lead to a denial of service or possibly unspecified other impact because limiting the additional noise energy level is mishandled for the G_max > G case.
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Analysis
by VulDB Data Team • 06/19/2023
The vulnerability identified as CVE-2018-20197 represents a critical stack-based buffer underflow within the Freeware Advanced Audio Decoder 2 version 2.8.8 library. This flaw exists specifically within the calculate_gain function located in the libfaad/sbr_hfadj.c source file, where improper handling of noise energy level limitations creates a condition that can be exploited through carefully crafted audio input data. The vulnerability manifests when the G_max parameter exceeds the G parameter during the audio processing calculations, leading to a mismanagement of memory boundaries that can result in unpredictable system behavior.
The technical nature of this vulnerability stems from improper bounds checking within the audio decoding algorithm that processes high frequency adjustment data in the spectral band replication component of FAAD2. When the audio decoder encounters malformed input where the maximum gain value surpasses the current gain value, the calculation routine fails to properly validate memory access patterns, resulting in underflow conditions that can overwrite adjacent stack memory locations. This type of flaw falls under the Common Weakness Enumeration category of CWE-121 Stack-based Buffer Overflow, which specifically addresses buffer overflows occurring in stack memory regions. The vulnerability demonstrates characteristics consistent with improper input validation and memory management practices that are commonly exploited in multimedia processing libraries.
The operational impact of this vulnerability extends beyond simple denial of service to potentially enable more sophisticated attack vectors. While the primary effect manifests as denial of service through application crashes or system instability, the underlying memory corruption could theoretically be leveraged for more advanced exploitation techniques. The vulnerability affects any system utilizing FAAD2 2.8.8 for audio decoding operations, including media players, streaming applications, and embedded systems that incorporate this library. The risk is particularly elevated in environments where users can provide arbitrary audio files, as the crafted input required to trigger this vulnerability can be embedded within legitimate audio content, making detection and prevention challenging.
Mitigation strategies for CVE-2018-20197 should prioritize immediate software updates to FAAD2 versions that have addressed this specific buffer underflow condition. System administrators and developers should implement strict input validation mechanisms that verify audio parameter ranges before processing, particularly focusing on gain value comparisons within the spectral band replication calculations. The implementation of defensive programming practices including bounds checking, memory sanitization, and input parameter validation can significantly reduce the risk of exploitation. Additionally, organizations should consider implementing network segmentation and access controls to limit exposure to potentially malicious audio content, while monitoring for unusual application behavior that might indicate exploitation attempts. This vulnerability aligns with ATT&CK technique T1203, which covers Obfuscated Files or Information, as attackers may embed malicious audio content to exploit such decoding vulnerabilities in multimedia applications.