CVE-2017-7758 in Firefox
Summary
by MITRE
An out-of-bounds read vulnerability with the Opus encoder when the number of channels in an audio stream changes while the encoder is in use. This vulnerability affects Firefox < 54, Firefox ESR < 52.2, and Thunderbird < 52.2.
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Analysis
by VulDB Data Team • 11/26/2025
The CVE-2017-7758 vulnerability represents a critical out-of-bounds read flaw within the Opus audio codec implementation in Mozilla Firefox and Thunderbird applications. This vulnerability specifically manifests when the audio stream undergoes channel count changes while the Opus encoder is actively processing audio data. The flaw occurs at the intersection of audio processing logic and memory management, creating a scenario where the encoder fails to properly validate channel count transitions during active encoding operations. The vulnerability is particularly concerning as it affects widely used email and web browser applications, potentially allowing attackers to exploit memory access violations through crafted audio content.
The technical root cause of this vulnerability lies in improper bounds checking within the Opus encoder's channel management logic. When the number of audio channels changes dynamically during encoding, the encoder does not adequately validate the new channel configuration against its internal buffer structures. This results in the encoder attempting to read memory locations beyond the allocated buffer boundaries, leading to information disclosure or potential code execution depending on the memory layout and exploitation conditions. The vulnerability maps to CWE-125 Out-of-bounds Read, which is classified as a memory safety issue that allows attackers to access memory locations they should not be able to reach. The flaw specifically impacts the encoder's ability to handle dynamic channel switching, where the internal state management fails to account for the transition from one channel configuration to another.
The operational impact of CVE-2017-7758 extends beyond simple information disclosure, as it creates potential vectors for more severe attacks within the browser and email client environments. When exploited, this vulnerability could allow attackers to extract sensitive information from the application's memory space, potentially including cryptographic keys, session tokens, or other confidential data. The vulnerability affects Firefox versions prior to 54 and Firefox ESR versions prior to 52.2, as well as Thunderbird versions prior to 52.2, representing a significant portion of deployed browser and email client installations. Attackers could leverage this vulnerability through malicious audio files embedded in web pages or email attachments, making it particularly dangerous in phishing campaigns or targeted attacks against users of affected software versions. The vulnerability also aligns with ATT&CK technique T1059 Command and Scripting Interpreter, as the exploitation could potentially involve executing malicious code through memory corruption.
Mitigation strategies for CVE-2017-7758 primarily focus on immediate software updates and patch management. Organizations should prioritize updating to Firefox 54 or later, Firefox ESR 52.2 or later, and Thunderbird 52.2 or later to address the vulnerability. Additionally, implementing network-based security controls such as content filtering and sandboxing mechanisms can provide defense-in-depth measures against exploitation attempts. Browser hardening techniques including disabling or restricting audio processing capabilities for untrusted content, implementing strict memory access controls, and using application whitelisting can further reduce the attack surface. Security teams should also monitor for indicators of compromise related to audio file handling and implement proper incident response procedures for potential exploitation attempts. The vulnerability serves as a reminder of the importance of proper input validation and bounds checking in multimedia processing libraries, particularly those handling real-time audio and video streams where dynamic parameter changes are common.