{ "document": { "category": "csaf_base", "csaf_version": "2.0", "distribution": { "tlp": { "label": "WHITE" } }, "lang": "en", "notes": [ { "category": "legal_disclaimer", "text": "The Netherlands Cyber Security Center (henceforth: NCSC-NL) maintains this portal to enhance access to its information and vulnerabilities. The use of this information is subject to the following terms and conditions:\n\nThe vulnerabilities disclosed in this portal are gathered by NCSC-NL from a variety of open sources, which the user can retrieve from other platforms. NCSC-NL makes every reasonable effort to ensure that the content of this portal is kept up to date, and that it is accurate and complete. Nevertheless, NCSC-NL cannot entirely rule out the possibility of errors, and therefore cannot give any warranty in respect of its completeness, accuracy or real-time keeping up-to-date. NCSC-NL does not control nor guarantee the accuracy, relevance, timeliness or completeness of information obtained from these external sources. The vulnerabilities disclosed in this portal are intended solely for the convenience of professional parties to take appropriate measures to manage the risks posed to the cybersecurity. No rights can be derived from the information provided therein.\n\nNCSC-NL and the Kingdom of the Netherlands assume no legal liability or responsibility for any damage resulting from either the use or inability of use of the vulnerabilities disclosed in this portal. This includes damage resulting from the inaccuracy of incompleteness of the information contained in it.\nThe information on this page is subject to Dutch law. All disputes related to or arising from the use of this portal regarding the disclosure of vulnerabilities will be submitted to the competent court in The Hague. This choice of means also applies to the court in summary proceedings." } ], "publisher": { "category": "coordinator", "contact_details": "cert@ncsc.nl", "name": "National Cyber Security Centre", "namespace": "https://www.ncsc.nl/" }, "title": "CVE-2026-33544", "tracking": { "current_release_date": "2026-04-03T17:03:00.100849Z", "generator": { "date": "2026-02-17T15:00:00Z", "engine": { "name": "V.E.L.M.A", "version": "1.7" } }, "id": "CVE-2026-33544", "initial_release_date": "2026-04-01T21:24:50.968618Z", "revision_history": [ { "date": "2026-04-01T21:24:50.968618Z", "number": "1", "summary": "CVE created.| Source created.| CVE status created. (valid)| Description created for source.| CVSS created.| References created (2).| CWES updated (1)." }, { "date": "2026-04-01T21:24:54.352333Z", "number": "2", "summary": "NCSC Score created." }, { "date": "2026-04-02T15:28:37.775729Z", "number": "3", "summary": "Source created.| CVE status created. (valid)| Description created for source.| CVSS created.| References created (3).| CWES updated (1)." }, { "date": "2026-04-02T15:28:40.414485Z", "number": "4", "summary": "NCSC Score updated." }, { "date": "2026-04-02T15:35:20.842327Z", "number": "5", "summary": "NCSC Score updated." }, { "date": "2026-04-02T15:41:44.578485Z", "number": "6", "summary": "Source created.| CVE status created. (valid)| Description created for source.| CVSS created.| Products created (1).| References created (3).| CWES updated (1)." }, { "date": "2026-04-02T15:41:53.767389Z", "number": "7", "summary": "NCSC Score updated." }, { "date": "2026-04-03T15:32:58.895773Z", "number": "8", "summary": "Source connected.| CVE status created. (valid)| EPSS created." }, { "date": "2026-04-03T15:33:07.792582Z", "number": "9", "summary": "NCSC Score updated." }, { "date": "2026-04-03T16:41:51.328323Z", "number": "10", "summary": "NCSC Score updated." } ], "status": "interim", "version": "10" } }, "product_tree": { "branches": [ { "branches": [ { "branches": [ { "category": "product_version_range", "name": "vers:unknown/<5.0.5", "product": { "name": "vers:unknown/<5.0.5", "product_id": "CSAFPID-5985007" } } ], "category": "product_name", "name": "tinyauth" } ], "category": "vendor", "name": "steveiliop56" } ] }, "vulnerabilities": [ { "cve": "CVE-2026-33544", "cwe": { "id": "CWE-362", "name": "Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')" }, "notes": [ { "category": "description", "text": "### Summary\n\nAll three OAuth service implementations (`GenericOAuthService`, `GithubOAuthService`, `GoogleOAuthService`) store PKCE verifiers and access tokens as mutable struct fields on singleton instances shared across all concurrent requests. When two users initiate OAuth login for the same provider concurrently, a race condition between `VerifyCode()` and `Userinfo()` causes one user to receive a session with the other user's identity.\n\n### Details\n\nThe [`OAuthBrokerService.GetService()`](https://github.com/steveiliop56/tinyauth/blob/592b7ded24959013f8af63ab9930254c752c8c8e/internal/service/oauth_broker_service.go#L70-L72) returns a single shared instance per provider for every request. The OAuth flow stores intermediate state as struct fields on this singleton:\n\n**Token storage** — [`generic_oauth_service.go` line 96](https://github.com/steveiliop56/tinyauth/blob/592b7ded24959013f8af63ab9930254c752c8c8e/internal/service/generic_oauth_service.go#L96):\n```go\ngeneric.token = token // Shared mutable field on singleton\n```\n\n**Verifier storage** — [`generic_oauth_service.go` line 81](https://github.com/steveiliop56/tinyauth/blob/592b7ded24959013f8af63ab9930254c752c8c8e/internal/service/generic_oauth_service.go#L81):\n```go\ngeneric.verifier = verifier // Shared mutable field on singleton\n```\n\nIn the callback handler [`oauth_controller.go` lines 136–143](https://github.com/steveiliop56/tinyauth/blob/592b7ded24959013f8af63ab9930254c752c8c8e/internal/controller/oauth_controller.go#L136-L143), the code calls:\n```go\nerr = service.VerifyCode(code) // line 136 — stores token on singleton\n// ... race window ...\nuser, err := controller.broker.GetUser(req.Provider) // line 143 — reads token from singleton\n```\n\nBetween these two calls, a concurrent request's `VerifyCode()` can overwrite the `token` field, causing `GetUser()` → `Userinfo()` to fetch the **wrong user's** identity claims.\n\nThe same pattern exists in all three implementations:\n- [`github_oauth_service.go` lines 34–39, 77, 86–99](https://github.com/steveiliop56/tinyauth/blob/592b7ded24959013f8af63ab9930254c752c8c8e/internal/service/github_oauth_service.go#L34-L39)\n- [`google_oauth_service.go` lines 22–27, 65, 73–87](https://github.com/steveiliop56/tinyauth/blob/592b7ded24959013f8af63ab9930254c752c8c8e/internal/service/google_oauth_service.go#L22-L27)\n\n### PoC\n\n**Race scenario** (two concurrent OAuth callbacks):\n\n1. User A and User B both click \"Login with GitHub\" on the same tinyauth instance\n2. Both are redirected to GitHub, authorize, and GitHub redirects both back with authorization codes\n3. Both callbacks arrive at tinyauth nearly simultaneously:\n\n```\nTimeline:\n t0: Request A → service.VerifyCode(codeA) → singleton.token = tokenA\n t1: Request B → service.VerifyCode(codeB) → singleton.token = tokenB (overwrites tokenA)\n t2: Request A → broker.GetUser(\"github\") → Userinfo() reads singleton.token = tokenB\n t3: Request A receives User B's identity (email, name, groups)\n```\n\nUser A now has a tinyauth session with User B's email, gaining access to all resources User B is authorized for via tinyauth's ACL.\n\n**PKCE verifier DoS variant**: Even with PKCE, concurrent `oauthURLHandler` calls overwrite the `verifier` field, causing `VerifyCode()` to send the wrong verifier to the OAuth provider, which rejects the exchange.\n\n**Static verification**: Run Go's race detector on a test that calls `VerifyCode` and `Userinfo` concurrently on the same service instance — the `-race` flag will flag data races on the `token` and `verifier` fields.\n\n**Go race detector confirmation**: Running a concurrent test with `go test -race` on the singleton service detects **4 data races** on the `token` and `verifier` fields. Without the race detector, measured token overwrite rate is 99.9% (9,985/10,000 iterations).\n\n**Test environment**: tinyauth v5.0.4, commit `592b7ded`, Go race detector + source code analysis\n\n### Impact\n\nAn attacker who times their OAuth callback to race with a victim's callback can obtain a tinyauth session with the victim's identity. This grants unauthorized access to all resources the victim is permitted to access through tinyauth's ACL system. The probability of collision increases with concurrent OAuth traffic.\n\nThe PKCE verifier overwrite additionally causes a denial-of-service: concurrent OAuth logins for the same provider reliably fail.\n\n### Suggested Fix\n\nPass verifier and token through method parameters or return values instead of storing them on the singleton:\n\n```go\nfunc (generic *GenericOAuthService) VerifyCode(code string, verifier string) (*oauth2.Token, error) {\n return generic.config.Exchange(generic.context, code, oauth2.VerifierOption(verifier))\n}\n\nfunc (generic *GenericOAuthService) Userinfo(token *oauth2.Token) (config.Claims, error) {\n client := generic.config.Client(generic.context, token)\n // ...\n}\n```\n\nStore the PKCE verifier in the session/cookie associated with the OAuth `state` parameter, not on the service struct.", "title": "github - https://api.github.com/advisories/GHSA-9q5m-jfc4-wc92" }, { "category": "description", "text": "Tinyauth is an authentication and authorization server. Prior to version 5.0.5, all three OAuth service implementations (GenericOAuthService, GithubOAuthService, GoogleOAuthService) store PKCE verifiers and access tokens as mutable struct fields on singleton instances shared across all concurrent requests. When two users initiate OAuth login for the same provider concurrently, a race condition between VerifyCode() and Userinfo() causes one user to receive a session with the other user's identity. This issue has been patched in version 5.0.5.", "title": "nvd - https://services.nvd.nist.gov/rest/json/cves/2.0?cveId=CVE-2026-33544" }, { "category": "description", "text": "Tinyauth is an authentication and authorization server. Prior to version 5.0.5, all three OAuth service implementations (GenericOAuthService, GithubOAuthService, GoogleOAuthService) store PKCE verifiers and access tokens as mutable struct fields on singleton instances shared across all concurrent requests. When two users initiate OAuth login for the same provider concurrently, a race condition between VerifyCode() and Userinfo() causes one user to receive a session with the other user's identity. This issue has been patched in version 5.0.5.", "title": "cveprojectv5 - https://raw.githubusercontent.com/CVEProject/cvelistV5/main/cves/2026/33xxx/CVE-2026-33544.json" }, { "category": "other", "text": "0.0004", "title": "EPSS" }, { "category": "other", "text": "4.3", "title": "NCSC Score" }, { "category": "other", "text": "There is product data available from source Cveprojectv5", "title": "NCSC Score top increasing factors" }, { "category": "other", "text": "There is cwe data available from source Nvd", "title": "NCSC Score top decreasing factors" } ], "product_status": { "known_affected": [ "CSAFPID-5985007" ] }, "references": [ { "category": "external", "summary": "Source - github", "url": "https://api.github.com/advisories/GHSA-9q5m-jfc4-wc92" }, { "category": "external", "summary": "Source - nvd", "url": "https://services.nvd.nist.gov/rest/json/cves/2.0?cveId=CVE-2026-33544" }, { "category": "external", "summary": "Source - cveprojectv5", "url": "https://raw.githubusercontent.com/CVEProject/cvelistV5/main/cves/2026/33xxx/CVE-2026-33544.json" }, { "category": "external", "summary": "Source - first", "url": "https://api.first.org/data/v1/epss?limit=10000&offset=0" }, { "category": "external", "summary": "Reference - cveprojectv5; github; nvd", "url": "https://github.com/steveiliop56/tinyauth/security/advisories/GHSA-9q5m-jfc4-wc92" }, { "category": "external", "summary": "Reference - github", "url": "https://github.com/advisories/GHSA-9q5m-jfc4-wc92" }, { "category": "external", "summary": "Reference - cveprojectv5; nvd", "url": "https://github.com/steveiliop56/tinyauth/commit/f26c2171610d5c2dfbba2edb6ccd39490e349803" }, { "category": "external", "summary": "Reference - cveprojectv5; nvd", "url": "https://github.com/steveiliop56/tinyauth/releases/tag/v5.0.5" } ], "scores": [ { "cvss_v3": { "version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:H/A:N", "baseScore": 7.7, "baseSeverity": "HIGH" }, "products": [ "CSAFPID-5985007" ] } ], "title": "CVE-2026-33544" } ] }