CVE-2026-35031

CriticalUpdated

Published: 14 April 2026

Published

14 April 2026

Modified

23 April 2026

KEV Added

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Patch

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CVSS Score 9.9 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

EPSS Score 0.0049 65.5th percentile

Risk Priority 20 60% EPSS · 20% KEV · 20% CVSS

Summary

CVE-2026-35031 is a critical-severity Improper Input Validation (CWE-20) vulnerability in Jellyfin Jellyfin. Its CVSS base score is 9.9 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked in the top 34.5% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified are NIST 800-53 SI-10 (Information Input Validation) and SI-2 (Flaw Remediation).

Threat & Defense at a Glance

What attackers do: exploitation maps to Exploit Public-Facing Application (T1190) and 2 other techniques. What defenders deploy: see the NIST 800-53 controls recommended below.

Threat & Defense Details

Mitigating Controls (NIST 800-53 r5)AI

SI-10 Information Input Validation good match

prevent

Directly addresses the improper input validation of the Format field that enables path traversal and arbitrary file writes in the subtitle upload endpoint.

SI-2 Flaw Remediation good match

prevent

Requires timely remediation of the known flaw fixed in Jellyfin 10.11.7, preventing exploitation of the vulnerability chain leading to RCE.

AC-6 Least Privilege partial match

prevent

Enforces least privilege to restrict subtitle upload permissions to only necessary users, reducing the attack surface as recommended in the advisory.

MITRE ATT&CK Enterprise TechniquesAI

T1190 Exploit Public-Facing Application Initial Access

Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.

attack.mitre.org →

T1068 Exploitation for Privilege Escalation Privilege Escalation

Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.

attack.mitre.org →

T1574.006 Dynamic Linker Hijacking Stealth

Adversaries may execute their own malicious payloads by hijacking environment variables the dynamic linker uses to load shared libraries.

attack.mitre.org →

Why these techniques?

CVE enables exploitation of public-facing web application (T1190) via path traversal for arbitrary file writes, chaining to privilege escalation (T1068) and RCE through ld.so.preload dynamic linker hijacking (T1574.006).

Confidence: HIGH · MITRE ATT&CK Enterprise v19.0

NVD Description

Jellyfin is an open source self hosted media server. Versions prior to 10.11.7 contain a vulnerability chain in the subtitle upload endpoint (POST /Videos/{itemId}/Subtitles), where the Format field is not validated, allowing path traversal via the file extension and enabling…

arbitrary file write. This arbitrary file write can be chained into arbitrary file read via .strm files, database extraction, admin privilege escalation, and ultimately remote code execution as root via ld.so.preload. Exploitation requires an administrator account or a user that has been explicitly granted the "Upload Subtitles" permission. This issue has been fixed in version 10.11.7. If users are unable to upgrade immediately, they can grant non-administrator users Subtitle upload permissions to reduce attack surface.

Deeper analysisAI

CVE-2026-35031 affects Jellyfin, an open-source self-hosted media server, in versions prior to 10.11.7. The vulnerability is a chain rooted in the subtitle upload endpoint (POST /Videos/{itemId}/Subtitles), where the Format field lacks validation. This enables path traversal through the file extension, resulting in arbitrary file writes. Associated CWEs include CWE-20 (Improper Input Validation), CWE-22 (Path Traversal), and CWE-187 (Incomplete Blacklist). The issue carries a CVSS v3.1 score of 9.9 (AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H).

Exploitation requires an administrator account or a user explicitly granted the "Upload Subtitles" permission. Attackers can leverage the initial arbitrary file write to chain into arbitrary file reads using .strm files, extract the database, escalate to admin privileges, and achieve remote code execution as root via ld.so.preload.

The vulnerability has been addressed in Jellyfin version 10.11.7. For those unable to upgrade immediately, the advisory recommends granting non-administrator users the Subtitle upload permission to minimize the attack surface. Additional details are available in the release notes at https://github.com/jellyfin/jellyfin/releases/tag/v10.11.7 and the security advisory at https://github.com/jellyfin/jellyfin/security/advisories/GHSA-j2hf-x4q5-47j3.