CVE-2021-21402 in Jellyfin
Summary
by MITRE • 03/24/2021
Jellyfin is a Free Software Media System. In Jellyfin before version 10.7.1, with certain endpoints, well crafted requests will allow arbitrary file read from a Jellyfin server's file system. This issue is more prevalent when Windows is used as the host OS. Servers that are exposed to the public Internet are potentially at risk. This is fixed in version 10.7.1. As a workaround, users may be able to restrict some access by enforcing strict security permissions on their filesystem, however, it is recommended to update as soon as possible.
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Analysis
by VulDB Data Team • 04/04/2021
The vulnerability identified as CVE-2021-21402 affects Jellyfin, a free software media system designed to provide digital media streaming capabilities. This security flaw represents a critical arbitrary file read vulnerability that allows attackers to access files stored on the server's file system through carefully crafted requests to specific endpoints. The vulnerability's severity is amplified when Jellyfin operates on Windows operating systems, making Windows-hosted installations particularly susceptible to exploitation. The issue creates a significant risk for publicly accessible servers since it enables unauthorized access to sensitive data that may be stored within the server's file system. Attackers could potentially retrieve configuration files, user credentials, media content, or other system files that should remain protected. This vulnerability directly impacts the confidentiality and integrity of the media system, as it allows for unauthorized data extraction without proper authentication or authorization mechanisms.
The technical implementation of this vulnerability stems from inadequate input validation and path traversal handling within Jellyfin's API endpoints. When users send crafted requests to specific endpoints, the application fails to properly sanitize or validate the input parameters that specify file paths or locations. This insufficient validation creates a path traversal condition where attackers can manipulate request parameters to navigate beyond the intended directory structure and access files that should be restricted. The vulnerability's prevalence on Windows systems suggests that the underlying file system handling mechanisms differ between operating systems, potentially due to how Windows manages file paths or how the application's file access routines process user-supplied input. The attack vector typically involves sending HTTP requests with specially constructed parameters that exploit the lack of proper path validation, allowing attackers to read files from arbitrary locations on the server's file system.
The operational impact of this vulnerability extends beyond simple data theft, as it can compromise the entire security posture of a Jellyfin deployment. Publicly exposed servers become potential entry points for attackers who can use this vulnerability to gather intelligence about the system, access sensitive configuration information, or extract user data. The vulnerability affects not just media files but potentially system configuration files, log files, and other sensitive data that may contain authentication credentials, system settings, or other confidential information. Organizations using Jellyfin for media streaming services face significant risks, particularly those handling user data or proprietary content. The vulnerability's exploitation can lead to complete system compromise, as attackers may discover additional vulnerabilities or use the stolen information to conduct further attacks. This type of vulnerability also impacts the trust relationship between service providers and users, as unauthorized access to user data can result in privacy violations and regulatory compliance issues.
The fix for CVE-2021-21402 was implemented in Jellyfin version 10.7.1, which introduced proper input validation and path sanitization mechanisms to prevent unauthorized file access. The recommended mitigation strategy involves immediate updating of all Jellyfin installations to version 10.7.1 or later, as this represents the most effective and reliable solution to address the vulnerability. While temporary workarounds such as implementing strict filesystem permissions can provide some protection, these measures are insufficient as primary defenses and should only be considered as interim solutions. Organizations should also implement network segmentation, firewall rules, and access controls to limit exposure of Jellyfin servers to untrusted networks. The vulnerability aligns with CWE-22, which describes path traversal or directory traversal flaws in software systems, and represents a specific instance of how improper input validation can lead to unauthorized data access. From an ATT&CK framework perspective, this vulnerability maps to techniques involving credential access and reconnaissance, as attackers can use it to gather system information and potentially escalate privileges through the access to sensitive files. Organizations should also conduct security audits to ensure no other similar vulnerabilities exist within their Jellyfin deployments and implement monitoring to detect suspicious file access patterns.