CVE-2024-40857 is a vulnerability classified under CWE-79 (Improper Neutralization of Input During Web Page Generation, commonly known as Cross-Site Scripting) that affects multiple Apple operating systems including macOS Sequoia 15, Safari 18, and other Apple platforms such as iOS 18 and visionOS 2. The root cause is improper state management within the browser engine that processes web content, allowing an attacker to craft malicious web pages that can execute arbitrary scripts in the context of trusted web origins. This universal cross-site scripting (UXSS) flaw enables attackers to bypass same-origin policy restrictions, potentially stealing sensitive information, manipulating web page content, or performing actions on behalf of the user without their consent. The vulnerability requires user interaction (e.g., visiting a malicious website) but does not require any privileges or authentication. The CVSS v3.1 base score is 6.1 (medium severity), reflecting network attack vector, low attack complexity, no privileges required, but user interaction needed, with limited confidentiality and integrity impact and no availability impact. Apple has addressed this issue through improved state management in the affected products, and patches are available in the latest OS and browser versions. No known exploits have been reported in the wild as of the publication date, but the vulnerability poses a significant risk to users of affected Apple products if left unpatched.

For European organizations, the primary impact of CVE-2024-40857 lies in the potential compromise of confidentiality and integrity of web sessions on Apple devices. Attackers exploiting this vulnerability could execute malicious scripts in the context of trusted websites, leading to theft of session cookies, credentials, or sensitive data, as well as unauthorized actions performed on behalf of users. This can affect web-based applications used in corporate environments, including email clients, intranet portals, and cloud services accessed via Safari or other Apple browsers. The vulnerability does not directly affect system availability but could facilitate further attacks such as phishing, data exfiltration, or lateral movement within networks. Organizations with a significant number of Apple device users, especially in sectors like finance, government, healthcare, and critical infrastructure, face increased risk. The need for user interaction means social engineering or phishing campaigns could be leveraged to trigger exploitation. Failure to patch could expose organizations to targeted attacks exploiting this UXSS flaw.

European organizations should implement a targeted patch management strategy to ensure all Apple devices are updated to the fixed versions: Safari 18, macOS Sequoia 15, iOS 18, iPadOS 18, visionOS 2, watchOS 11, and tvOS 18. Beyond applying patches, organizations should enforce strict web browsing policies, including disabling or restricting the use of Safari for sensitive operations if feasible. Deploy endpoint protection solutions capable of detecting and blocking malicious web content or scripts. Educate users on the risks of interacting with unknown or suspicious websites to reduce the likelihood of user-driven exploitation. Implement Content Security Policy (CSP) headers on internal web applications to mitigate the impact of XSS attacks. Monitor network traffic and logs for unusual activity indicative of exploitation attempts. For high-risk environments, consider using browser isolation technologies or alternative browsers with different rendering engines until patches are fully deployed. Regularly review and update incident response plans to include scenarios involving browser-based script injection attacks.