Description

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.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "4.3",
  "pubDate": "2026-09-29T13:17:43.247Z",
  "pubdate": "2026-09-29T13:17:43.247Z",
  "executiveSummary": "A critical security vulnerability involving uninitialized memory has been identified within the Audio/Video component of Firefox. This flaw stems from improper memory management, where the application fails to initialize memory buffers before reading data during media processing operations.\nThe vulnerability affects multiple versions of Firefox, including Firefox ESR 153.4, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17. If exploited, this defect allows an attacker to potentially access sensitive information residing in memory, leading to an information disclosure risk.\nAttackers can leverage this vulnerability by tricking a user into interacting with maliciously crafted media content. Successful exploitation relies on the browser's ability to trigger the path where uninitialized memory is accessed. Given the nature of media processing, the risk to confidentiality is significant, as attackers may be able to exfiltrate snippets of heap or stack data, which could contain security tokens, credentials, or other private user information.\nNo authentication or specific privileges are required by the attacker, as the attack is typically delivered through standard web-based interactions. Users are encouraged to update their browsers immediately to versions containing the security patches.",
  "technicalDetails": "The vulnerability resides within the Audio/Video parsing or playback pipeline of the Firefox browser engine. Specifically, it involves a state where memory is allocated for a media buffer but is not explicitly cleared or zero-initialized before the rendering component attempts to perform read operations on that memory space. This is a classic case of uninitialized memory access, which frequently occurs when complex media formats—such as those processed by hardware acceleration layers or platform-specific codecs—fail to adhere to secure memory initialization practices.\nThe root cause is likely an incorrect assumption within the memory allocation logic where the developer assumes the operating system or the underlying allocator provides zeroed memory, or where a code path skips initialization during error-handling sequences. During the lifecycle of a media object, a parser may allocate a structure meant to hold metadata, frame data, or audio samples. If the parser encounters a malformed or intentionally crafted bitstream that triggers an early exit or an incomplete parsing cycle, the subsequent consumer of this structure may read memory contents from previous operations.\nThe attack flow typically begins with the delivery of a malicious media file (e.g., an MP4 or WebM container) via a web page or an iframe. When the browser's Audio/Video component attempts to process this file, the crafted structure forces the parser to allocate a memory buffer that is subsequently left partially or fully uninitialized. When the browser proceeds to display the video or play the audio, it reads the stale data from the heap. An attacker who can influence the state of the heap—perhaps by 'spraying' the heap with controlled data before the trigger occurs—may be able to guide the content read from the uninitialized buffer.\nThis vulnerability is particularly concerning because it crosses the boundary between controlled media processing and raw memory inspection. By carefully manipulating the media metadata, an attacker can coerce the browser into performing an 'out-of-bounds read' or 'uninitialized read' to expose sensitive pointers or data structures previously stored in that memory segment. Post-exploitation impact ranges from sensitive information disclosure to the potential bypassing of security mitigations like ASLR (Address Space Layout Randomization) by leaking memory addresses, which could facilitate a more complex RCE (Remote Code Execution) chain."
}