Description

Privilege escalation due to incorrect boundary conditions in the Audio/Video component. This vulnerability was fixed in Firefox 156 and Firefox ESR 153.3.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "8.8",
  "pubDate": "2026-09-15T13:16:55.750Z",
  "pubdate": "2026-09-15T13:16:55.750Z",
  "executiveSummary": "A critical security vulnerability has been identified within the Audio/Video processing component of the Firefox browser. The vulnerability stems from incorrect boundary conditions during the handling of media data, which could be leveraged by an attacker to achieve unauthorized privilege escalation.\nThe flaw affects Firefox versions prior to 156 and Firefox ESR versions prior to 153.3. By exploiting this boundary condition error, a malicious actor could potentially manipulate memory operations to elevate privileges beyond the sandbox constraints typically imposed on the web content process.\nThe risk implication is severe, as successful exploitation may allow for arbitrary code execution or unauthorized system access within the context of the browser environment. This vulnerability does not explicitly require user interaction beyond navigating to a malicious resource, though it necessitates that the attacker can provide crafted media input that triggers the out-of-bounds state.\nOrganizations and individual users are urged to update to the latest versions, as this vulnerability represents a significant breach of the browser's security model, specifically compromising the isolation guarantees between the web content and the host operating system.",
  "technicalDetails": "The vulnerability is rooted in an improper boundary condition check within the Audio/Video media parsing engine of Firefox. In complex media processing pipelines, the browser must validate the lengths, sizes, and offsets of data structures provided in media files (such as those containing specific container formats or codec streams) before copying them into allocated memory buffers.\nIn this specific instance, the Audio/Video component fails to correctly validate the boundaries of incoming media data, leading to a condition where an out-of-bounds (OOB) memory access can occur. This typically manifests as a heap-based buffer overflow or an OOB read/write, depending on the specific codec path and the metadata structure involved.\nThe exploitation flow begins when a user loads a webpage containing a maliciously crafted media resource. The browser's media engine initializes the parsing of this content, and the flawed boundary check is triggered during the processing of malformed data fields. Because the validation logic is insufficient, the engine attempts to perform operations—such as copying media buffers—outside the intended memory boundaries.\nAn attacker can weaponize this by crafting specific media payloads that overwrite adjacent memory structures in the browser's heap. By carefully controlling the heap layout, an attacker might overwrite object pointers, virtual function tables (vtable), or other control-flow-sensitive structures. This allows the attacker to redirect the browser's execution flow toward an attacker-controlled payload, often bypassing Address Space Layout Randomization (ASLR) and Data Execution Prevention (DEP) through techniques such as Return-Oriented Programming (ROP).\nOnce the execution flow is successfully hijacked, the attacker can execute arbitrary code with the privileges of the Firefox content process. To escalate privileges further, the attacker may attempt to exploit secondary vulnerabilities or leverage the initial code execution to interact with IPC (Inter-Process Communication) mechanisms, potentially breaking out of the sandbox to execute code with the user's full privileges on the underlying host operating system.\nThis vulnerability specifically targets the internal media handling functions, which are often written in C++ and require rigorous bounds checking. The absence of adequate sanitization for untrusted input provided via standard HTML5 media tags makes this a potent vector for remote attackers who can serve content via standard HTTP/HTTPS protocols."
}