CVE-2025-54143 in Firefox
Summary
by MITRE • 08/20/2025
Sandboxed iframes on webpages could potentially allow downloads to the device, bypassing the expected sandbox restrictions declared on the parent page. This vulnerability was fixed in Firefox for iOS 141.
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Analysis
by VulDB Data Team • 10/06/2026
This vulnerability represents a critical sandbox escape mechanism that undermines the fundamental security model of web content isolation. The issue manifests specifically within Firefox for iOS versions prior to 141 where sandboxed iframes can potentially bypass the intended restrictions that should prevent them from initiating downloads to the underlying device. The sandboxing mechanism is designed to isolate potentially malicious content from the host system and other web pages, but this flaw allows for unauthorized file operations that should remain restricted. The vulnerability exploits the trust model between the browser and its sandboxed content, creating a pathway for arbitrary file system access that could lead to data exfiltration or system compromise.
The technical flaw stems from improper enforcement of sandbox security boundaries when processing iframe content within the iOS browser environment. When a webpage contains a sandboxed iframe, the browser should maintain strict isolation between the iframe content and the host device, preventing the iframe from performing operations such as file downloads, system calls, or access to local resources. However, this vulnerability demonstrates that under specific conditions, the sandbox restrictions can be circumvented, allowing the iframe to execute download operations directly to the device storage. The flaw likely resides in how Firefox for iOS handles permission checks and security boundary enforcement when processing download requests originating from sandboxed contexts, potentially failing to validate that the requesting context has appropriate authorization levels.
The operational impact of this vulnerability extends beyond simple unauthorized downloads, presenting significant risks to user privacy and system integrity. Attackers could craft malicious web pages that embed specially constructed iframes designed to download sensitive files from the device or install malicious software without user consent. This capability could enable targeted attacks against iOS users, particularly in scenarios where users might visit compromised websites or be tricked into clicking on malicious links. The vulnerability is particularly concerning in mobile environments where device security is paramount, as iOS users expect robust isolation between web content and their device's file system. The impact is amplified by the fact that this affects the iOS version of Firefox, which may be used by users who rely on the browser for sensitive activities such as banking, email, or accessing confidential corporate data.
Mitigation strategies should prioritize immediate patching of affected Firefox for iOS versions to ensure users are protected against this sandbox escape vulnerability. Organizations should implement browser security policies that restrict the use of sandboxed iframes on sensitive applications and consider deploying additional network-level controls to monitor for suspicious download activities. Users should be educated about the risks of visiting untrusted websites and the importance of keeping their browser software updated. Security professionals should monitor for exploitation attempts targeting this vulnerability and consider implementing sandbox monitoring tools that can detect unauthorized file operations from sandboxed contexts. The vulnerability aligns with CWE-276, which addresses improper privileges, and may map to ATT&CK techniques related to privilege escalation and persistence through browser-based attacks. Regular security audits should verify that sandboxing mechanisms are properly enforced and that no unauthorized access paths exist between web content and system resources.