CVE-2025-64113: 
C# vulnerability analysis and mitigation

CVE-2025-64113 is a critical authentication bypass vulnerability in Emby Server caused by a weak password recovery mechanism (CWE-640) that allows unauthenticated attackers to gain full administrative access to the Emby Server application. It affects all stable Emby Server versions up to and including 4.9.1.80, and all beta versions up to and including 4.9.2.6. The vulnerability was published on December 6, 2025 by researcher 'tembybot' via the Emby Security advisory repository, and assigned CVE-2025-64113 on December 9, 2025. It carries a CVSS v3.1 base score of 9.8 (Critical) and a CVSS v4.0 base score of 9.3 (Critical) (Emby Advisory, Github Advisory).

The root cause is classified as CWE-640 (Weak Password Recovery Mechanism for Forgotten Password): Emby Server's ForgotPassword API endpoint improperly handles the password reset flow, relying on a file (passwordreset.txt) in the server's configuration directory in a way that can be abused by an unauthenticated remote attacker. By interacting with this API, an attacker can bypass authentication entirely and obtain full administrative privileges over the Emby Server management interface — without requiring any prior credentials, user interaction, or special network position. The attack is network-accessible, low-complexity, and requires no privileges, making it trivially exploitable against any internet-exposed Emby Server instance (Emby Advisory, Github Advisory).

Successful exploitation grants an attacker complete administrative control over the Emby Server application, including the ability to modify or delete media libraries, manage user accounts, alter server configurations, and access all administrative functions. While the compromise is scoped to the Emby Server administration layer (not OS-level access), the high confidentiality, integrity, and availability impact means an attacker could expose user data, disrupt media services, and potentially pivot to other systems if Emby is integrated with broader infrastructure. All users of vulnerable Emby Server instances — including their personal media and account credentials stored within Emby — are at risk (Emby Advisory).

As of the time of disclosure, no public proof-of-concept exploit code has been confirmed, though a GitHub repository (Ashwesker/Blackash-CVE-2025-64113) appeared shortly after disclosure, suggesting community interest in weaponization. There is no confirmed evidence of in-the-wild exploitation, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. The EPSS score is approximately 0.024% (7th percentile), indicating a currently low but non-negligible probability of exploitation in the near term. The zero-precondition nature of the attack (network access only) significantly lowers the barrier for exploitation (Github Advisory, Feedly).

1. Reconnaissance: Identify internet-facing Emby Server instances using tools like Shodan or Censys, searching for Emby Server web interfaces (typically on port 8096 or 8920). Target instances running versions 4.9.1.80 or earlier (stable) or 4.9.2.6-beta or earlier.
2. Trigger the ForgotPassword API: Send an unauthenticated HTTP request to the Emby Server's ForgotPassword API endpoint. This creates or interacts with the passwordreset.txt file in the server's configuration directory.
3. Abuse the weak recovery mechanism: Exploit the weak password recovery logic to obtain or set administrative credentials without knowing the original password, leveraging the flawed handling of the passwordreset.txt file.
4. Authenticate as administrator: Use the recovered or reset credentials to log into the Emby Server administration interface with full administrative privileges.
5. Post-exploitation: With admin access, enumerate user accounts and credentials, modify server settings, access media libraries, or use the administrative interface to further pivot within the environment (Emby Advisory).

• Network: Unexpected or repeated unauthenticated HTTP requests to the Emby Server ForgotPassword API endpoint from external or unknown IP addresses; unusual administrative API calls following a password reset request.
• Logs: Emby Server access logs showing ForgotPassword API calls from IPs not associated with legitimate administrators; subsequent admin-level actions (user creation, config changes) immediately following a password reset event.
• File System: Presence or unexpected modification of passwordreset.txt in the Emby Server configuration directory; new or modified admin user accounts in Emby's user database.
• Application: Unexpected changes to Emby Server configuration, media library settings, or user account roster; new administrator accounts created without corresponding legitimate activity (Emby Advisory).

Emby has released patched versions: 4.9.1.90 for stable releases and 4.9.2.7 for beta releases — all Emby Server owners should update immediately. As an emergency interim measure (now marked obsolete by the vendor), administrators could restrict file system permissions on passwordreset.txt in the Emby configuration folder: on Windows, set DENY permissions for "Authenticated users"; on Linux, run sudo chmod 444 passwordreset.txt. Additionally, a quick fix was distributed via an automatic plugin update to reach servers that are not manually updated. Network-level controls — such as firewall rules restricting access to the Emby administration interface to trusted IPs — are recommended as a defense-in-depth measure (Emby Advisory, Github Advisory).

The vulnerability received coverage from multiple security news outlets including SecurityOnline, CyberSecurityNews, and The Hacker News (in a weekly recap), reflecting broad community awareness. Social media activity was noted on Bluesky, with infosec accounts flagging the critical severity and zero-precondition nature of the flaw. The Emby team responded promptly with both a plugin-based quick fix and full server patches, and the advisory was published transparently via a dedicated GitHub security repository. The GitHub advisory was later partially withdrawn (December 29, 2025) to correct an erroneous listing of the MediaBrowser.Server.Core NuGet package as vulnerable, clarifying that only the Emby Server application itself is affected (Github Advisory, SecurityOnline, CyberSecurityNews).