CVE-2021-29490 in Jellyfin
Summary
by MITRE • 05/06/2021
Jellyfin is a free software media system that provides media from a dedicated server to end-user devices via multiple apps. Verions prior to 10.7.3 vulnerable to unauthenticated Server-Side Request Forgery (SSRF) attacks via the imageUrl parameter. This issue potentially exposes both internal and external HTTP servers or other resources available via HTTP `GET` that are visible from the Jellyfin server. The vulnerability is patched in version 10.7.3. As a workaround, disable external access to the API endpoints `/Items/*/RemoteImages/Download`, `/Items/RemoteSearch/Image` and `/Images/Remote` via reverse proxy, or limit to known-friendly IPs.
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Analysis
by VulDB Data Team • 05/09/2021
The CVE-2021-29490 vulnerability affects Jellyfin, a free software media system designed to deliver media content from centralized servers to end-user devices through various applications. This particular flaw represents a critical security weakness that allows unauthenticated attackers to exploit server-side request forgery mechanisms within the platform. The vulnerability specifically manifests through the imageUrl parameter, which creates a pathway for malicious actors to manipulate the system's behavior and potentially access resources otherwise restricted from external viewing.
The technical implementation of this vulnerability stems from insufficient input validation and sanitization within the Jellyfin server's image handling functionality. When processing image requests through the affected parameters, the system fails to properly validate or restrict the URLs being processed, allowing attackers to craft malicious requests that can traverse the network and access internal resources. This flaw operates at the server level where the application makes HTTP GET requests to external resources, but due to inadequate security controls, these requests can be manipulated to target internal systems or services that are accessible from the Jellyfin server's network context.
The operational impact of this vulnerability extends beyond simple data exposure, as it potentially allows attackers to enumerate internal network services, access sensitive information, and possibly escalate their privileges within the network environment. The vulnerability can expose both internal and external HTTP servers that are visible from the Jellyfin server's perspective, creating a significant attack surface that could lead to further compromise of the infrastructure. This issue is particularly concerning because it enables attackers to leverage the Jellyfin server as a pivot point for reconnaissance and exploitation of other systems within the same network segment.
Security professionals should note that this vulnerability aligns with CWE-918, which specifically addresses server-side request forgery flaws, and can be mapped to ATT&CK technique T1071.004 for application layer protocol usage. The patched version 10.7.3 implements proper input validation and URL restriction mechanisms that prevent unauthorized access to internal resources. Organizations can implement several mitigation strategies including disabling external access to the vulnerable API endpoints through reverse proxy configuration, restricting access to known trusted IP addresses, and implementing network segmentation controls. Additionally, regular security updates and monitoring of system logs for suspicious activity related to image processing requests should be implemented as part of the overall security posture.
The remediation approach requires immediate deployment of Jellyfin version 10.7.3 or later, which contains the necessary patches to address the SSRF vulnerability. Organizations should also conduct thorough network assessments to identify any potential exploitation attempts and implement proper access controls for the affected API endpoints. The workaround measures suggested by the vendor provide temporary relief but do not address the root cause, making the official patch the preferred long-term solution. Security teams should monitor their environments for any signs of exploitation attempts and ensure that all Jellyfin installations are kept up to date with the latest security releases to prevent similar vulnerabilities from being exploited in the future.