Plex-configured Seerr instances vulnerable to unauthenticated account registration via Jellyfin authentication endpoint

{
  "id": "f9ea3a81b81801c10c0dce57797efc4ba919a8df448ec7ead5c7fc0a959e39b4",
  "url": "https://osv.dev/vulnerability/CVE-2026-27707",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Plex-configured Seerr instances vulnerable to unauthenticated account registration via Jellyfin authentication endpoint",
    "summary": "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.",
    "evidence": "osv:CVE-2026-27707",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-27707",
      "aliases": [
        "CVE-2026-27707",
        "GHSA-rc4w-7m3r-c2f7"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/seerr-team/seerr",
              "type": "GIT",
              "events": [
                {
                  "introduced": "63dfe003b0852d6307772abd331ffde8686e8c17"
                },
                {
                  "fixed": "94a70bb5fc9a4486857071a6fc048c8081fa7ca9"
                },
                {
                  "fixed": "4ae20684092b5b28527b23dfbc1a3417858fee8e"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:seerr:seerr:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "2.0.0"
                      },
                      {
                        "fixed": "3.1.0"
                      }
                    ],
                    "source": "CPE_RANGE"
                  },
                  {
                    "range": [
                      {
                        "fixed": "4ae20684092b5b28527b23dfbc1a3417858fee8e"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  },
                  {
                    "range": [
                      {
                        "fixed": "94a70bb5fc9a4486857071a6fc048c8081fa7ca9"
                      }
                    ],
                    "source": "REFERENCES_TAG",
                    "original_tag": "v3.1.0"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v3.0.1",
            "v3.0.0",
            "v2.7.3",
            "v2.7.2",
            "v2.7.1",
            "v2.7.0",
            "v2.6.0",
            "v2.5.2",
            "v2.5.1",
            "v2.5.0",
            "v2.4.0",
            "v2.3.0",
            "v2.2.3",
            "v2.2.2",
            "v2.2.1",
            "v2.2.0",
            "v2.1.0",
            "v2.0.1",
            "v2.0.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-27707.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:46.290795861Z",
      "provider": "osv",
      "references": [
        "https://github.com/seerr-team/seerr/releases/tag/v3.1.0",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/27xxx/CVE-2026-27707.json",
        "https://github.com/seerr-team/seerr/security/advisories/GHSA-rc4w-7m3r-c2f7",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-27707",
        "https://github.com/seerr-team/seerr/commit/4ae20684092b5b28527b23dfbc1a3417858fee8e"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-288",
          "CWE-807"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/27xxx/CVE-2026-27707.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-27707",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 514114,
  "published_at": "2026-02-27T19:29:18.768+00:00"
}