CVE-2018-20194 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 CVE-2018-20194 represents a critical stack-based buffer underflow within the Freeware Advanced Audio Decoder 2 version 2.8.8, specifically within the libfaad/sbr_hfadj.c component. This issue manifests in the third instance of the calculate_gain function where improper handling of noise energy level limiting creates a dangerous condition that can be exploited by malicious actors. The flaw occurs when the maximum gain level G_max is less than or equal to the current gain G, causing the system to mishandle additional noise energy levels in a manner that violates memory boundaries.
The technical implementation of this vulnerability stems from inadequate input validation and memory management within the audio decoding process. When processing crafted audio input data, the calculate_gain function fails to properly constrain buffer operations during noise energy level calculations, leading to memory corruption that can result in program termination or unpredictable behavior. This type of buffer underflow falls under the CWE-121 category of stack-based buffer overflow conditions, where the attacker can manipulate the program's execution flow by overwriting adjacent stack memory locations. The vulnerability specifically impacts the high frequency adjustment processing within the FAAD2 decoder, which is responsible for handling advanced audio coding formats including aac and aacplus.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as the buffer underflow can potentially enable more sophisticated attacks depending on the execution environment. When exploited successfully, the vulnerability may allow attackers to cause application crashes, leading to service disruption for legitimate users, or in more severe cases, could potentially be leveraged to execute arbitrary code if the affected system lacks proper memory protection mechanisms. The nature of audio decoding applications makes them particularly susceptible to such vulnerabilities since they often process untrusted input from various sources without adequate sanitization. This vulnerability affects systems that utilize FAAD2 as their audio decoding library, including media players, streaming applications, and embedded systems that handle audio content processing.
Mitigation strategies for CVE-2018-20194 should prioritize immediate patching of the FAAD2 library to version 2.8.9 or later, which includes fixes for the buffer underflow condition. System administrators should implement input validation measures to prevent malformed audio data from reaching the decoder, particularly in environments where user-supplied content is processed. Network-based defenses can include content filtering mechanisms that scan audio streams for suspicious patterns that may indicate crafted malicious inputs. The vulnerability demonstrates the importance of proper boundary checking and input validation in audio processing libraries, aligning with ATT&CK technique T1203 which covers legitimate program execution through process injection. Organizations should also consider implementing runtime protections such as stack canaries and address space layout randomization to reduce the exploitability of similar buffer overflow conditions in their audio processing pipelines. Regular security assessments of multimedia libraries and components should be conducted to identify and remediate similar vulnerabilities before they can be exploited in real-world scenarios.