CVE-2026-100783 in Firefox
Summary
by MITRE • 09/29/2026
Uninitialized memory in the Audio/Video component. This vulnerability was fixed in Firefox ESR 153.4, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17.
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Analysis
by VulDB Data Team • 09/29/2026
The identified security issue represents an uninitialized memory access within the Audio/Video subsystem of Mozilla Firefox browsers. This type of vulnerability typically arises when a variable or data structure is allocated in memory but not properly initialized with default values before being read or used by subsequent operations. In the context of multimedia processing, such as audio and video decoding or rendering, this flaw can lead to unpredictable behavior because the software may interpret random garbage data from adjacent memory locations as valid instructions or configuration parameters. The presence of uninitialized memory is a critical concern in web browser engines due to their complex interaction with external media files and plugins, which are often supplied by untrusted third parties on the internet.
From a technical perspective, this vulnerability aligns closely with Common Weakness Enumeration (CWE) identifiers such as CWE-457, which describes the use of an uninitialized variable, or potentially CWE-908 if it involves the use of uninitialized pointer values that could lead to arbitrary code execution. The root cause likely lies in a logic error within the media pipeline where memory buffers are reused without being cleared, or where conditional branches fail to initialize specific fields under certain edge cases. When an attacker crafts a malicious audio or video file with specific structural anomalies, they may trigger this uninitialized read path. Depending on how the browser handles the resulting garbage data, this could lead to information disclosure if sensitive memory contents are leaked back to the webpage via side channels, or more severely, it could facilitate heap corruption and arbitrary code execution if the uninitialized values influence control flow decisions or pointer arithmetic within the media decoder components.
The operational impact of such a vulnerability is significant because browsers process multimedia content frequently during normal user activity. An attacker hosting a malicious website containing specially crafted audio or video assets could potentially exploit this flaw to achieve remote code execution on the victim's machine without any further interaction, assuming other browser security mitigations like sandboxing are bypassed or fail. This places users at risk of full system compromise, including data theft, installation of malware, and use of the compromised device for botnet activities. The vulnerability affects multiple versions of Firefox, indicating a systemic issue in the underlying media handling libraries that persisted across several release cycles until addressed.
To mitigate this risk, it is imperative to update all instances of Mozilla Firefox to the patched versions listed: Firefox ESR 153.4, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17. These updates contain code changes that ensure proper initialization of memory buffers within the Audio/Video components before they are accessed or processed. Organizations should enforce automated patch management policies to ensure timely deployment of these security fixes across all endpoints running affected browser versions. Additionally, users can reduce their exposure by disabling unnecessary media plugins and keeping operating system-level sandboxing features enabled, which provide an additional layer of defense against exploitation attempts even if the application-layer vulnerability were present in unpatched software.