CVE-2019-6956 in Freeware Advanced Audio Decoder
Summary
by MITRE
An issue was discovered in Freeware Advanced Audio Decoder 2 (FAAD2) 2.8.8. It is a buffer over-read in ps_mix_phase in libfaad/ps_dec.c.
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Analysis
by VulDB Data Team • 08/26/2025
The vulnerability identified as CVE-2019-6956 affects the Freeware Advanced Audio Decoder 2 version 2.8.8, a widely used open-source audio decoding library that implements the Advanced Audio Coding standard. This decoder is commonly integrated into various multimedia applications, streaming platforms, and embedded systems where audio processing is essential. The flaw manifests within the ps_mix_phase function located in the libfaad/ps_dec.c source file, representing a critical buffer over-read condition that could potentially compromise system stability and security.
The technical implementation of this vulnerability stems from inadequate input validation within the psychoacoustic processing stage of audio decoding. When the ps_mix_phase function processes specific malformed audio data streams, it fails to properly bounds-check array accesses, leading to memory access beyond allocated buffer boundaries. This over-read condition occurs during the phase synthesis operations that are fundamental to the perceptual coding algorithms used in advanced audio formats such as AAC. The flaw specifically impacts the handling of phase information in the stereo processing component, where insufficient validation allows attackers to craft malicious audio inputs that trigger the buffer over-read behavior.
The operational impact of this vulnerability extends beyond simple denial-of-service scenarios, as it represents a potential security risk that could be exploited in various attack vectors. An attacker could potentially leverage this vulnerability through crafted audio files delivered via web applications, media streaming services, or file transfer protocols that utilize FAAD2 for audio decoding. The buffer over-read could lead to arbitrary code execution, system crashes, or information disclosure depending on the execution environment and memory layout. This vulnerability affects the broader ecosystem of applications relying on FAAD2, including media players, streaming servers, and embedded devices with audio processing capabilities.
Mitigation strategies for CVE-2019-6956 should prioritize immediate software updates to FAAD2 versions that contain the patched ps_mix_phase implementation. Organizations should conduct comprehensive vulnerability assessments of their systems to identify all applications utilizing FAAD2, particularly those handling untrusted audio input streams. Security controls should include input validation mechanisms, sandboxing of audio processing components, and network segmentation to limit potential exploitation paths. The vulnerability aligns with CWE-129, which addresses insufficient validation of length of inputs, and may map to ATT&CK techniques involving code injection and privilege escalation through memory corruption vulnerabilities. System administrators should implement monitoring for unusual memory access patterns and ensure regular patch management protocols are in place to address similar buffer over-read vulnerabilities in multimedia libraries.