CVE-2025-43526 in Safari
Summary
by MITRE • 12/17/2025
This issue was addressed with improved URL validation. This issue is fixed in macOS Tahoe 26.2, Safari 26.2. On a Mac with Lockdown Mode enabled, web content opened via a file URL may be able to use Web APIs that should be restricted.
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Analysis
by VulDB Data Team • 12/17/2025
This vulnerability represents a significant security regression in Apple's macOS Tahoe 26.2 and Safari 26.2 implementations where the enhanced URL validation measures failed to properly restrict Web API access for content opened through file URLs. The flaw specifically manifests when Lockdown Mode is enabled on Mac systems, creating an unexpected privilege escalation vector that undermines the security model designed to isolate potentially malicious web content. The vulnerability stems from inadequate validation of file URL schemes that should normally be restricted from accessing certain Web APIs, effectively allowing web content to bypass security boundaries that are typically enforced for local file access.
The technical implementation flaw resides in the URL parsing and security boundary enforcement mechanisms within Safari's WebKit rendering engine. When Lockdown Mode is active, the system should enforce strict isolation between local file content and Web APIs that could potentially be exploited for malicious purposes. However, the validation process fails to properly identify when file URLs are being used to load web content, allowing the loaded content to access APIs that should be restricted to prevent cross-origin attacks, local file system access, or other privilege escalation vectors. This represents a classic security boundary violation that can be categorized under CWE-284 Access Control Issues where improper access controls allow unauthorized access to restricted resources.
The operational impact of this vulnerability is particularly severe in environments where Lockdown Mode is enabled, which is designed to provide maximum security isolation for users who may be targeted by sophisticated attacks. Attackers could potentially exploit this flaw by crafting malicious web content that is opened through file URLs, thereby gaining access to restricted Web APIs that could be used to exfiltrate data, execute arbitrary code, or perform other malicious activities. The vulnerability affects the core security model of Lockdown Mode, which is specifically designed to prevent such scenarios by ensuring that local file content cannot access privileged Web APIs that could be used to compromise system security. This undermines the fundamental security assumptions that users rely on when enabling Lockdown Mode for protection against advanced persistent threats.
Mitigation strategies should focus on immediate deployment of the patched versions macOS Tahoe 26.2 and Safari 26.2 where the URL validation has been improved to properly enforce security boundaries for file URLs. System administrators should ensure that all affected systems are updated promptly, particularly in environments where Lockdown Mode is actively used. Additionally, monitoring should be implemented to detect any attempts to access restricted Web APIs from file URL content, as this could indicate exploitation attempts. The fix addresses the underlying validation logic to properly distinguish between different URL schemes and enforce appropriate access controls for each type of content, aligning with the ATT&CK technique T1059 Command and Scripting Interpreter where attackers might attempt to leverage Web APIs to execute malicious code or exfiltrate data through compromised browser security boundaries. Organizations should also consider implementing additional network-level monitoring to detect unusual patterns of Web API access that could indicate exploitation of this vulnerability.