Refresh Token Leaked via URL Query Parameter in OAuth Provider Callback

{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/nhost/nhost"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.0.0-20260330133707-294954e0fc3a"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-34969"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-200",
      "CWE-598"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-04-01T23:36:10Z",
    "nvd_published_at": "2026-04-06T16:16:38Z",
    "severity": "LOW"
  },
  "details": "# Refresh Token Leaked via URL Query Parameter in OAuth Provider Callback\n\n## Summary\n\nThe auth service\u0027s OAuth provider callback flow places the refresh token directly into the redirect URL as a query parameter. Refresh tokens in URLs are logged in browser history, server access logs, HTTP Referer headers, and proxy/CDN logs.\n\nNote that the refresh token is one-time use and all of these leak vectors are on owned infrastructure or services integrated by the application developer.\n\n## Affected Component\n\n- **Repository**: `github.com/nhost/nhost`\n- **Service**: `services/auth`\n- **File**: `services/auth/go/controller/sign_in_provider_callback_get.go`\n- **Function**: `signinProviderProviderCallback` (lines 257-261)\n\n## Root Cause\n\nIn `sign_in_provider_callback_get.go:257-261`, after successful OAuth sign-in, the refresh token is appended as a URL query parameter:\n\n```go\nif session != nil {\n    values := redirectTo.Query()\n    values.Add(\"refreshToken\", session.RefreshToken)\n    redirectTo.RawQuery = values.Encode()\n}\n```\n\nThis results in a redirect like:\n```\nHTTP/1.1 302 Found\nLocation: https://myapp.com/callback?refreshToken=a1b2c3d4-e5f6-7890-abcd-ef1234567890\n```\n\n## Proof of Concept\n\n### Step 1: Initiate OAuth login\n```\nGET /signin/provider/github?redirectTo=https://myapp.com/callback\n```\n\n### Step 2: Complete OAuth flow with provider\n\n### Step 3: Auth service redirects with token in URL\n```\nHTTP/1.1 302 Found\nLocation: https://myapp.com/callback?refreshToken=a1b2c3d4-e5f6-7890-abcd-ef1234567890\n```\n\n### Step 4: Token is now visible in owned infrastructure and services:\n\n**Browser History:**\n```\n# User\u0027s browser history now contains the refresh token\n```\n\n**HTTP Referer Header:**\n```\n# If the callback page loads ANY external resource (image, script, etc.):\nGET /resource.js HTTP/1.1\nHost: cdn.example.com\nReferer: https://myapp.com/callback?refreshToken=a1b2c3d4-e5f6-...\n# Note: modern browsers default to strict-origin-when-cross-origin policy,\n# which strips query parameters from cross-origin Referer headers.\n# Additionally, the Referer is only sent to services integrated by the\n# application developer (analytics, CDNs, etc.), not arbitrary third parties.\n```\n\n**Server Access Logs:**\n```\n# Reverse proxy, CDN, or load balancer logs on owned infrastructure:\n2026-03-08 12:00:00 GET /callback?refreshToken=a1b2c3d4-e5f6-... 200\n```\n\n### Step 5: Attacker uses stolen refresh token\n```bash\n# Exchange stolen refresh token for new access token\ncurl -X POST https://auth.nhost.run/v1/token \\\n  -H \u0027Content-Type: application/json\u0027 \\\n  -d \u0027{\"refreshToken\": \"a1b2c3d4-e5f6-7890-abcd-ef1234567890\"}\u0027\n\n# Note: refresh tokens are one-time use, so this only works if the\n# legitimate client has not already consumed the token and if the attacker has\n# compromised your infrastructure to get access to this information\n```\n\n## Impact\n\n1. **Session Hijacking**: Anyone who obtains the token before it is consumed by the legitimate client can generate new access tokens, though the refresh token is one-time use and cannot be reused after consumption.\n\n2. **Leak Vectors**: URL query parameters are visible in owned infrastructure and integrated services:\n   - Browser history (local access)\n   - HTTP Referer headers (mitigated by modern browser default referrer policies; only sent to developer-integrated services)\n   - Server access logs (owned infrastructure)\n   - Proxy/CDN/WAF logs (owned infrastructure)\n\n3. **Affects All OAuth Providers**: Every OAuth provider flow (GitHub, Google, Apple, etc.) goes through the same callback handler.\n\n## Fix\n\nImplemented PKCE (Proof Key for Code Exchange) for the OAuth flow. With PKCE, the authorization code cannot be exchanged without the `code_verifier` that only the original client possesses, preventing token misuse even if the URL is logged.\n\nSee: https://docs.nhost.io/products/auth/pkce/\n\n## Resources\n\n- OWASP: Session Management - Token Transport: \"Session tokens should not be transported in the URL\"\n- RFC 6749 Section 10.3: \"Access tokens and refresh tokens MUST NOT be included in the redirect URI\"\n- CWE-598: Use of GET Request Method With Sensitive Query Strings\n- CWE-200: Exposure of Sensitive Information to an Unauthorized Actor",
  "id": "GHSA-g2qj-prgh-4g9r",
  "modified": "2026-04-06T23:25:15Z",
  "published": "2026-04-01T23:36:10Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/nhost/nhost/security/advisories/GHSA-g2qj-prgh-4g9r"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-34969"
    },
    {
      "type": "WEB",
      "url": "https://docs.nhost.io/products/auth/pkce"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/nhost/nhost"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Nhost Leaks Refresh Tokens via URL Query Parameter in OAuth Provider Callback"
}