CVE-2026-55982: Gitea OIDC Userinfo Endpoint Returns Identity Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-mg4f-x9v4-6h2p",
  "modified" : "2026-07-21T20:42:05Z",
  "published" : "2026-07-21T20:42:05Z",
  "aliases" : [ "CVE-2026-55982" ],
  "summary" : "Gitea: OIDC userinfo Endpoint Returns Identity Claims Without Enforcing API Token Scopes",
  "details" : "### Summary\n\nThe OIDC userinfo endpoint (`GET /login/oauth/userinfo`) accepts Gitea API tokens as bearer credentials but does not enforce API token scopes before returning identity claims.\n\nA personal access token scoped only to `read:misc` can successfully retrieve user information from the OIDC userinfo endpoint, even though the same token is denied access to user-related REST API endpoints that enforce scope checks.\n\nAs a result, identity information remains accessible through the OIDC endpoint regardless of the scopes assigned to the API token.\n\n### Details\n\nGitea supports scoped personal access tokens and enforces scope checks on user-related REST API endpoints.\n\nFor example, a token scoped only to `read:misc` is denied access to endpoints such as:\n\n| Endpoint | Required Scope |\n|----------|----------------|\n| `GET /api/v1/user` | `read:user` |\n| `GET /api/v1/user/emails` | `read:user` |\n| `GET /api/v1/user/orgs` | `read:organization` |\n\nRequests to these endpoints return:\n\n```http\n403 Forbidden\n```\n\nwith a scope-related error.\n\nHowever, the same `read:misc` token can be supplied as a bearer credential to:\n\n```http\nGET /login/oauth/userinfo\nAuthorization: Bearer <token>\n```\n\nand receives a successful response containing identity claims.\n\nObserved claims include:\n\n- `email`\n- `groups`\n\nThe `groups` claim contains organization and team membership information associated with the authenticated user.\n\nThis behavior indicates that the OIDC userinfo endpoint accepts API tokens but does not apply scope restrictions before returning identity claims.\n\n### PoC\n\n#### PoC Details\n\nProof-of-concept code: \nhttps://anonymous.4open.science/r/Gitea_PoC-EC93/3_poc_oidc_userinfo_scope_bypass\n\n#### Reproduction Steps\n\n1. Create a personal access token with only the following scope:\n\n```text\nread:misc\n```\n\n2. Verify that the token cannot access user-related REST API endpoints:\n\n```http\nGET /api/v1/user\nGET /api/v1/user/emails\nGET /api/v1/user/orgs\n```\n\nEach request returns:\n\n```http\n403 Forbidden\n```\n\n3. Send the same token to the OIDC userinfo endpoint:\n\n```http\nGET /login/oauth/userinfo\nAuthorization: Bearer <read-misc-token>\n```\n\n4. Observe that the request succeeds and returns identity claims, for example:\n\n```json\n{\n  \"email\": \"user@example.com\",\n  \"groups\": [\n    ...\n  ]\n}\n```\n\n### Impact\n\nHolders of narrowly scoped API tokens can obtain identity information through the OIDC userinfo endpoint regardless of the scopes assigned to the token.\n\nThe issue does not provide access to repositories, issues, pull requests, administrative functionality, or data belonging to other users.\n\nImpact is limited to disclosure of identity information associated with the authenticated user. However, it weakens the authorization boundary established by API token scopes because identity claims remain accessible even when the token lacks user- or organization-related scopes.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "code.gitea.io/gitea"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.27.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/go-gitea/gitea/security/advisories/GHSA-mg4f-x9v4-6h2p"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/go-gitea/gitea"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/go-gitea/gitea/releases/tag/v1.27.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-200" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-21T20:42:05Z",
    "nvd_published_at" : null
  }
}