Review reviewHigh

CVE-2026-49247

jellyfin

Jellyfin is an open source self hosted media server. From 10.9.0 until 10.11.10, the POST /ClientLog/Document endpoint accepts the Authorization header's Client and Version fields and uses them unsanitized as components of the on-disk filename when persisting client-uploaded log documents. As a result, any authenticated non-admin user can include ../ sequences in the Client field to cause Jellyfin to write attacker-controlled content to arbitrary paths reachable by the Jellyfin service user, with a forced .log suffix. This vulnerability is fixed in 10.11.10.

CVSS: 8.8
EPSS: 0.34%
CISA KEV: Not listed
Published: 2026.06.25

PRIORITY ASSESSMENT

Review review

The CVSS severity warrants an early asset and exposure review.

Known exploitationNot established by KEV

Exploit probability0.34%

Technical severityCVSS 8.8

Vulnerability overview

Affected product and versions

Product: jellyfin
Affected versions: >= 10.9.0, < 10.11.10
Fixed versions: No verified fixed-version field is available yet

Recommended response sequence

Confirm exposure before applying a vendor-supported change.

Full remediation guide

1
Identify
Confirm that jellyfin and an affected version are present.
2
Prioritize
Combine exploitation signals with asset exposure and business criticality.
3
Remediate
Follow the vendor advisory or supported update path and preserve rollback options.
4
Verify
Recheck the version, service health, access paths, and relevant logs.

Technical data

CVSS vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
CWE: CWE-22