CVE-2024-30931 is a stored Cross Site Scripting (XSS) vulnerability identified in Emby Media Server version 4.8.3.0, specifically within the notifications.html component. Stored XSS occurs when malicious input is saved by the application and later rendered in users' browsers without proper sanitization or encoding. In this case, an unauthenticated remote attacker can inject malicious JavaScript code into the notifications interface, which is then executed in the context of other users viewing the notifications page. This can lead to privilege escalation by hijacking user sessions, stealing sensitive information, or performing unauthorized actions within the Emby Media Server environment. The vulnerability is rated with a CVSS v3.1 score of 6.1, indicating a medium severity level. The attack vector is network-based (remote), requires no privileges, but does require user interaction (the victim must load the malicious notification). The scope is changed (S:C), meaning the vulnerability can affect resources beyond the initially vulnerable component. The impact affects confidentiality and integrity but not availability. No patches or known exploits are currently available, but the vulnerability is publicly disclosed, which could lead to future exploitation attempts. The root cause is improper input validation and output encoding in the notifications.html component, a common issue classified under CWE-79 (Improper Neutralization of Input During Web Page Generation).

The primary impact of CVE-2024-30931 is the potential compromise of user confidentiality and integrity within Emby Media Server environments. Attackers exploiting this stored XSS vulnerability can execute arbitrary scripts in the context of other users, potentially stealing authentication tokens, session cookies, or other sensitive data. This can lead to unauthorized access or privilege escalation within the media server, allowing attackers to manipulate user settings, access restricted content, or disrupt normal operations. Although availability is not directly impacted, the breach of confidentiality and integrity can undermine trust and lead to further attacks. Organizations relying on Emby Media Server for media streaming or content management could face data leakage, unauthorized control, or reputational damage. Since the vulnerability requires user interaction but no authentication, it poses a significant risk especially in environments where multiple users access the server interface. The lack of a patch increases the window of exposure until a fix is released.

To mitigate CVE-2024-30931, organizations should implement the following specific measures: 1) Restrict access to the Emby Media Server interface to trusted users and networks, using network segmentation and firewall rules to limit exposure. 2) Disable or restrict the notifications feature if it is not essential, reducing the attack surface. 3) Monitor and audit notifications content for suspicious or unexpected entries that could indicate attempted exploitation. 4) Employ Content Security Policy (CSP) headers to limit the execution of unauthorized scripts in the browser context. 5) Educate users to avoid interacting with suspicious notifications or links within the Emby interface. 6) Regularly check for official patches or updates from Emby and apply them promptly once available. 7) Consider deploying Web Application Firewalls (WAFs) with rules to detect and block XSS payloads targeting the notifications component. 8) Conduct internal code reviews and penetration testing focused on input validation and output encoding in the notifications.html component to identify and remediate similar issues proactively.