CVE-2026-111728 in Seanime
Summary
by MITRE • 10/16/2026
Seanime v3.7.0 to v3.10.3 contains an argument injection vulnerability reachable through improper authorization, allowing unauthenticated LAN or Tailnet clients to bypass the privileged mediastream settings guard by setting transcodeHwAccel to custom and supplying attacker-controlled decodeFlags and encodeFlags via the transcodeHwAccelCustomSettings field, which are appended verbatim to the ffmpeg argument vector. Attackers can trigger execution via the mediastream request and HLS playlist endpoints to achieve arbitrary file write and file truncation on the host as the user running seanime, with the injected input options also enabling potential arbitrary local file read and outbound data exfiltration through ffmpeg's protocol handlers.
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Analysis
by VulDB Data Team • 10/16/2026
Seanime versions 3.7.0 through 3.10.3 are susceptible to a critical argument injection vulnerability stemming from improper authorization controls within its media streaming subsystem. This flaw allows unauthenticated clients, whether operating on the local area network or connected via Tailnet, to bypass privileged mediastream settings guards that are intended to restrict access to administrative configurations. The core technical failure lies in how the application handles user-supplied input for hardware acceleration settings. Specifically, when a client sets the transcodeHwAccel parameter to custom and provides values for decodeFlags and encodeFlags through the transcodeHwAccelCustomSettings field, these inputs are not subjected to adequate sanitization or validation before being processed by the underlying media transcoding engine.
The vulnerability manifests as an argument injection flaw where attacker-controlled strings are appended verbatim to the ffmpeg command line argument vector. Because ffmpeg is a powerful multimedia framework that supports a wide array of input and output protocols, this direct insertion enables attackers to inject arbitrary commands into the execution context. The attack surface includes both the mediastream request endpoint and the HLS playlist generation endpoint, providing multiple vectors for exploitation without requiring prior authentication or elevated privileges on the target system. This lack of authorization enforcement means that any network-accessible client can trigger the vulnerable code path.
The operational impact of this vulnerability is severe, primarily due to the context in which ffmpeg executes. The media processing tasks typically run with the permissions of the user account under which the Seanime service operates. Consequently, successful exploitation allows an attacker to achieve arbitrary file write and file truncation on the host system at the discretion of that user. This capability can lead to complete compromise of the server's integrity if the service runs with elevated privileges or targets critical configuration files. Furthermore, the injected input options leverage ffmpeg’s extensive protocol handler support, enabling potential arbitrary local file read operations by specifying sensitive local paths as inputs for transcoding tasks.
Beyond direct file manipulation and reading, this vulnerability facilitates outbound data exfiltration. By manipulating the output parameters within the injected arguments, an attacker can redirect media streams or extracted files to remote servers controlled by the adversary using ffmpeg’s supported network protocols such as HTTP, RTMP, or SFTP. This transforms a local configuration flaw into a significant data loss risk, allowing sensitive content from the host system to be transmitted externally without detection through standard application logging mechanisms that may not inspect low-level command line arguments.
From a classification perspective, this vulnerability aligns with CWE-78 Improper Neutralization of Special Elements used in an OS Command and CWE-269 Improvement of Privileges due to improper authorization checks. The exploitation technique maps directly to MITRE ATT&CK techniques including T1059 Command and Scripting Interpreter for the execution aspect, T1048 Encryption Exfiltration if encrypted channels are utilized during exfiltration, and potentially T1003 OS Credential Dumping or T1005 Data from Local System depending on which files are targeted. The combination of argument injection with weak access control creates a high-severity risk profile that demands immediate remediation.
Mitigation strategies should prioritize updating Seanime to version 3.10.4 or later, where these input validation and authorization checks have been addressed. In the interim, organizations must implement strict network segmentation to restrict access to media streaming endpoints from untrusted networks. Additionally, deploying web application firewalls with rules capable of detecting ffmpeg argument injection patterns can provide a layer of defense against exploitation attempts. Running the Seanime service under a restricted user account with minimal file system permissions and disabling unnecessary protocol handlers in ffmpeg configurations further reduces the blast radius should an exploit be attempted.