CVE-2026-27840: Github.com/zitadel/zitadel ZITADEL's Truncated Opaque Tokens Are Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-6mq3-xmgp-pjm5",
  "modified" : "2026-02-27T21:22:00Z",
  "published" : "2026-02-27T21:22:00Z",
  "aliases" : [ "CVE-2026-27840" ],
  "summary" : "ZITADEL's truncated opaque tokens are still valid",
  "details" : "### Summary\n\nOpaque OIDC access tokens in v2 format, truncated to 80 characters are still considered valid. \n\nZITADEL uses a symmetric AES encryption for opaque tokens. The cleartext payload is a concatenation of a couple of identifiers, such as a token ID and user ID. Internally Zitadel has 2 different versions of token payloads. v1 tokens are no longer created, but are still verified as to not invalidate existing session after upgrade.\n\nThe cleartext payload has a format of `<token_id>:<user_id>`. v2 tokens distinguished further where the `token_id` is of the format `v2_<oidc_session_id>-at_<access_token_id>`. This is an example of such a cleartext: `V2_354201447279099906-at_354201447279165442:354201364702363650`\n\n### Impact\n\nV1 token authZ/N session data is retrieved from the database using the (simple) `token_id` value and `user_id` value. The `user_id` (called `subject` in some parts of our code) was used as being the trusted user ID.\n\nV2 token authZ/N session data is retrieved from the database using the `oidc_session_id` and `access_token_id` and in this case the `user_id` from the token is ignored and taken from the session data in the database.\n\nBy truncating the token to 80 chars, the user_id is now missing from the cleartext of the v2 token: `V2_354201447279099906-at_354201447279165442:`  The back-end still accepts this for above reasons.\n\nThis issue is not considered exploitable, but may look awkward when reproduced.\n\n### Affected Versions\n\nAll versions within the following ranges, including release candidates (RCs), are affected:\n- **v4.x**: `4.0.0` through `4.10.1`\n- **3.x**: `3.0.0` through `3.4.6`\n- **2.x**: `2.31.0` through `2.71.19`\n\n### Patches\n\nThe vulnerability has been addressed in the latest releases. The patch resolves the issue by verifying the `user_id` from the token against the session data from the database\n\n4.x: Upgrade to >=[4.11.0](https://github.com/zitadel/zitadel/releases/tag/v4.11.0)\n3.x: Update to >=[3.4.7](https://github.com/zitadel/zitadel/releases/tag/v3.4.7)\n2.x: Update to >=[3.4.7](https://github.com/zitadel/zitadel/releases/tag/v3.4.7)\n\n### Workarounds\n\nThe recommended solution is to update ZITADEL to a patched version.\n\n### Questions\n\nIf there any questions or comments about this advisory, please send an email to [security@zitadel.com](mailto:security@zitadel.com)\n\n### Credits\n\nZITADEL thanks Olivier Becker and Lucas Dodgson for reporting this vulnerability.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/zitadel/zitadel"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.0.0"
      }, {
        "fixed" : "4.11.0"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/zitadel/zitadel"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "3.0.0"
      }, {
        "fixed" : "3.4.7"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/zitadel/zitadel"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.31.0"
      }, {
        "last_affected" : "2.71.19"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/zitadel/zitadel"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.80.0-v2.20.0.20260216092519-feab8e1fa371"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/zitadel/zitadel/security/advisories/GHSA-6mq3-xmgp-pjm5"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-27840"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/zitadel/zitadel/commit/feab8e1fa371f3ad654640fc869b2c14f2fdb602"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/zitadel/zitadel"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/zitadel/zitadel/releases/tag/v2.71.19"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/zitadel/zitadel/releases/tag/v3.4.7"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/zitadel/zitadel/releases/tag/v4.11.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-302" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-02-27T21:22:00Z",
    "nvd_published_at" : "2026-02-26T01:16:25Z"
  }
}