CVE-2026-119549 in Jellyfin
Summary
by MITRE • 10/30/2026
Jellyfin through 12.4 contains a server-side request forgery vulnerability that lets authenticated users bypass SvgSecurityValidator by embedding gzip-compressed SVG in non-SVG image data URIs. Attackers can upload such profile images via POST /UserImage, then trigger unauthenticated rendering via GET /UserImage to fetch internal URLs, read local image files, or exhaust memory.
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Analysis
by VulDB Data Team • 10/30/2026
The vulnerability identified in Jellyfin versions through 12.4 represents a critical server-side request forgery flaw rooted in the improper validation of input data within the user profile image handling mechanism. This specific weakness allows authenticated users to bypass security controls designed to restrict access to internal resources or prevent malicious file processing. The core technical issue lies in how the application processes SVG images embedded within non-SVG image data URIs, specifically when these payloads are gzip-compressed. By exploiting this logic error, an attacker can circumvent the SvgSecurityValidator, which is intended to sanitize and validate SVG content to prevent XSS attacks or other injection-based exploits. The vulnerability stems from a failure in the input validation pipeline where the application does not adequately inspect the underlying structure of compressed archives before rendering them as images, allowing maliciously crafted payloads to slip through initial security checks.
From an operational perspective, this flaw enables authenticated attackers to perform server-side request forgery attacks against internal services that are otherwise inaccessible from the public internet. By uploading a specially constructed profile image via the POST /UserImage endpoint and subsequently triggering its rendering through GET /UserImage, an attacker can force the Jellyfin server to make HTTP requests to arbitrary URLs specified within the SVG payload. This capability allows for several detrimental outcomes including reading local files on the server if they are accessible via file:// protocols or internal network paths, probing internal services such as databases or administrative interfaces running on localhost, and potentially causing denial of service conditions by exhausting server memory through resource-intensive rendering operations. The ability to read local image files further exacerbates the risk by enabling information disclosure beyond just network reconnaissance.
This vulnerability aligns with CWE-918 Server-Side Request Forgery (SSRF) as it involves manipulating a web application into making requests on behalf of an attacker to unintended destinations. Additionally, the exploitation technique relates to CWE-20 Improper Input Validation because the system fails to correctly validate and sanitize user-supplied input before processing it for rendering. In terms of offensive security frameworks, this attack vector corresponds to ATT&CK T1598 Phishing via Server-Side Request Forgery or more broadly to reconnaissance activities under T1496 Resource Hijacking if used for denial of service purposes. The exploitation requires authentication initially but leverages that access to perform actions typically reserved for unauthenticated users, thereby escalating the impact from a simple account compromise to potential internal network penetration and data exfiltration.
Mitigation strategies should focus on immediate patching to version 12.5 or later where this validation logic has been corrected. Administrators must ensure that all Jellyfin instances are updated promptly as no reliable workaround exists other than restricting access to the application itself. For environments where updates cannot be applied immediately, network-level controls such as firewall rules blocking outbound connections from the Jellyfin server IP address to internal subnets can provide a partial mitigation by preventing successful SSRF requests even if they are triggered. Furthermore, implementing strict Content Security Policies and ensuring that image processing libraries used internally do not support dangerous SVG features like external entity resolution or script execution will help reduce the attack surface for similar vulnerabilities in other components of the media server infrastructure.