CVE-2026-49220
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedJellyfin is an open source self hosted media server. Prior to 10.11.9, a potential XSS attack exists in Jellyfin which can allow a non-privileged user to execute arbitrary Javascript in the context of a logged-in Administrative user, resulting in numerous potential issues. The Client header during an AuthenticateByName can contain arbitrary HTML and Javascript, which will then be executed by the Administrative user when visiting the Access tab of the user in question from within the dashboard. This vulnerability is fixed in 10.11.9.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceA stored XSS vulnerability exists in Jellyfin where a non-privileged user can inject arbitrary HTML and JavaScript via the Client header during the AuthenticateByName process. This malicious payload executes when an Administrative user views the Access tab of the compromised user from the Jellyfin dashboard, allowing the attacker to run code in the admin's session context.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- Low
- User interaction
- Required
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- None
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:N/A:N
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify your Jellyfin server versionLog into the Jellyfin dashboard as an administrator, then navigate to Dashboard > General. The server version is displayed at the top of the page. Alternatively, query the /System/Info API endpoint.Affected if The installed version is earlier than 10.11.9 (the fixed release).
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Verify the Authentication endpoint is accessibleConfirm the Jellyfin web interface or API is reachable at your server URL. The vulnerable endpoint is /Users/AuthenticateByName which accepts custom Client header values.Affected if Jellyfin is exposed and allows authentication requests with custom HTTP headers.
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Review user account Client valuesAs an administrator, navigate to Dashboard > Users. For each user, click the user name to open their profile, then access the Access tab. Inspect the Client field to see if any unexpected or suspicious values are present that were not intentionally set.Affected if Any non-administrative user account displays an unexpected or encoded value in the Client field on their Access tab, indicating potential injection.
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Check server logs for suspicious authentication attemptsExamine Jellyfin logs (Dashboard > Logging) for entries containing the /Users/AuthenticateByName endpoint with unusual Client header patterns, such as HTML tags, script elements, or encoded characters.Affected if Logs show authentication attempts with Client headers containing <script>, javascript:, or similar XSS payloads.
You are affected if your Jellyfin version is earlier than 10.11.9 AND any user account displays an unexpected value in their Client Access field, indicating the XSS payload was stored and could execute in an administrator's session.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scopedUpgrade Jellyfin to version 10.11.9 or later. As a temporary measure, administrative users should avoid accessing user Access tabs from untrusted sources until the patch is applied.
10.11.9
- Upgrade Jellyfin to version 10.11.9 or later to remediate this XSS vulnerability
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation2.0 h
- Implementation3.0 h
- Testing3.0 h
- Review / QA2.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2026-49220 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-49220 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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