EUVD-2026-15990
CVSS Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
Lifecycle Timeline
3Description
Sonarr is a PVR for Usenet and BitTorrent users. Versions prior to 4.0.16.2942 have an authentication bypass that affected users that had disabled authentication for local addresses (Authentication Required set to: `Disabled for Local Addresses`) without a reverse proxy running in front of Sonarr that didn't not pass through the invalid header. Patches are available in version 4.0.16.2942 in the nightly/develop branch and version 4.0.16.2944 for stable/main releases. Some workarounds are available. Make sure Sonarr's Authentication Required setting is set to `Enabled`, run Sonarr behind a reverse proxy, and/or do not expose Sonarr directly to the internet and instead rely on accessing it through a VPN, Tailscale or a similar solution.
Analysis
Sonarr, a PVR application for Usenet and BitTorrent users, contains an authentication bypass vulnerability affecting installations configured with authentication disabled for local addresses. Attackers can exploit this flaw to gain unauthorized access to Sonarr instances when deployed without a properly configured reverse proxy that filters malicious headers. …
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Remediation
Within 24 hours: Identify all Sonarr deployments and document which have authentication disabled for local addresses. Within 7 days: Implement network segmentation to restrict Sonarr access or deploy a reverse proxy with strict header validation. …
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External POC / Exploit Code
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