CVE-2025-51497 is a privacy and information disclosure vulnerability identified in the AdGuard browser extension for Safari on macOS, specifically in versions prior to 1.11.22. The issue arises from the plugin's verbose logging behavior, where every URL accessed by Safari while the plugin is active is recorded in the macOS general system logs. These logs are accessible to any unsandboxed process on the system, meaning that any application or process without strict sandboxing restrictions can read these logs and potentially extract sensitive browsing history information. This behavior effectively leaks user browsing activity to other local processes, compromising user privacy and potentially exposing sensitive or confidential URLs. The vulnerability does not require user interaction beyond having the vulnerable plugin installed and active, and it does not require authentication to exploit since local processes can access the logs directly. The vendor addressed this issue by disabling or limiting this verbose logging behavior starting with AdGuard version 1.11.22. No known exploits are reported in the wild as of the publication date. The vulnerability primarily impacts confidentiality by exposing browsing data, but it does not directly affect system integrity or availability. Given the nature of the vulnerability, it is a local information disclosure flaw rather than a remote code execution or privilege escalation issue.

For European organizations, this vulnerability poses a significant privacy risk, especially for employees or users who browse sensitive corporate or personal websites using Safari with the vulnerable AdGuard plugin installed. The leakage of URLs to other local processes could lead to unauthorized disclosure of confidential business information, intellectual property, or personally identifiable information (PII). In regulated sectors such as finance, healthcare, and government, such data leakage could result in compliance violations with GDPR and other privacy regulations, potentially leading to fines and reputational damage. Additionally, adversaries with local access to affected machines could leverage this vulnerability to gather intelligence on user browsing habits or identify targets for further attacks. While the vulnerability requires local access, the widespread use of macOS devices in European enterprises and the popularity of Safari as a browser mean that the attack surface is non-trivial. The impact is heightened in environments where endpoint security controls are lax or where multiple users share the same machine. However, since the vulnerability does not allow remote exploitation or privilege escalation, its impact is limited to confidentiality breaches rather than system compromise or denial of service.

European organizations should take the following specific mitigation steps: 1) Immediately update the AdGuard Safari plugin to version 1.11.22 or later, where the verbose logging behavior is disabled. 2) Conduct an inventory of macOS devices to identify installations of the vulnerable AdGuard plugin and prioritize patching on devices used by high-risk users or in sensitive departments. 3) Implement strict endpoint security policies that restrict unsandboxed processes and limit access to system logs, thereby reducing the risk of local processes reading sensitive logs. 4) Educate users about the risks of installing browser plugins from unverified sources and encourage the use of privacy-respecting extensions. 5) Monitor macOS system logs for unusual access patterns or unauthorized processes attempting to read logs, using endpoint detection and response (EDR) tools. 6) Consider deploying application whitelisting or sandboxing solutions to limit the ability of unauthorized local processes to access system logs. 7) Review and update privacy and security policies to ensure compliance with GDPR and other relevant regulations concerning data leakage and endpoint security.