CVE-2018-20198 in Freeware Advanced Audio Decoder
Summary
by MITRE
A NULL pointer dereference was discovered in ifilter_bank of libfaad/filtbank.c in Freeware Advanced Audio Decoder 2 (FAAD2) 2.8.8. The vulnerability causes a segmentation fault and application crash, which leads to denial of service because adding to windowed output is mishandled in the LONG_START_SEQUENCE case.
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Analysis
by VulDB Data Team • 06/19/2023
The vulnerability identified as CVE-2018-20198 represents a critical NULL pointer dereference flaw within the Freeware Advanced Audio Decoder 2 version 2.8.8 implementation. This issue resides in the ifilter_bank function located within the libfaad/filtbank.c source file, which forms a core component of the FAAD2 audio decoding library. The flaw specifically manifests during the processing of audio data streams where the decoder fails to properly validate pointer references before dereferencing them, creating a scenario where a null pointer access can occur during normal operation.
The technical execution of this vulnerability occurs when the decoder encounters a LONG_START_SEQUENCE case within its windowed output processing logic. During this particular decoding path, the application attempts to manipulate audio filter bank data without first ensuring that the necessary memory references are properly initialized or validated. This improper handling results in a segmentation fault when the system tries to access memory through a NULL pointer reference, causing the application to terminate abruptly and leading to a complete denial of service condition for legitimate users attempting to process audio content.
The operational impact of this vulnerability extends beyond simple application crashes as it creates a reliable denial of service vector that can be exploited by malicious actors. When an attacker crafts specially formatted audio files or streams that trigger the specific LONG_START_SEQUENCE processing path, they can reliably crash any application utilizing the FAAD2 library. This vulnerability affects a wide range of software systems including media players, streaming applications, and any other software that incorporates the FAAD2 audio decoding library for processing aac audio files. The flaw's exploitation requires no special privileges and can be executed through normal audio file processing operations, making it particularly dangerous in environments where automated audio processing occurs.
From a cybersecurity perspective, this vulnerability maps directly to CWE-476 which defines NULL Pointer Dereference as a weakness where a null pointer is dereferenced, and it aligns with ATT&CK technique T1499.004 which covers Network Denial of Service. The flaw demonstrates poor input validation and memory management practices within the audio decoding pipeline, where proper error handling and pointer validation mechanisms are missing. Organizations using FAAD2 in their audio processing pipelines should immediately implement mitigations including updating to patched versions of the library, implementing input validation controls, and deploying intrusion detection systems to monitor for exploitation attempts. The vulnerability underscores the importance of proper memory management in multimedia libraries and highlights the need for comprehensive testing of edge cases in audio format processing to prevent similar issues in other audio decoding implementations.