EUVD-2026-84011Severity by source
AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
Authenticated low-privilege user (PR:L) can trivially (AC:L, no UI) bypass per-app authorization over the network; impact scales to full read/write of the protected app (C:H/I:H), no availability effect.
Primary rating from Vendor (GitHub_M).
CVSS VectorVendor: GitHub_M
Lifecycle Timeline
4DescriptionCVE.org
Tinyauth is an authentication and authorization server. Prior to 5.1.2, Tinyauth compares forwarded hostnames case-sensitively while reverse proxies route equivalent hostnames case-insensitively, allowing an authenticated low-privilege user to bypass per-app access controls with a differently cased hostname. The lookup in internal/service/access_controls_service.go through lookupStaticACLs and GetAccessControls, and the Docker-label fallback in internal/service/docker_service.go through GetLabels, can miss the configured app and return an empty access-control object. internal/controller/proxy_controller.go proxyHandler then treats the empty user, group, OAuth, LDAP, and IP restrictions as permissive and returns an authenticated result for an app that should exclude the user. Unauthenticated users remain subject to login, and global login-time allowlists are not bypassed. This issue is fixed in version 5.1.2.
AnalysisAI
Authorization bypass in Tinyauth releases prior to 5.1.2 allows an authenticated, low-privilege user to reach applications whose per-app access controls are configured to exclude them. Tinyauth matches forwarded hostnames case-sensitively in lookupStaticACLs/GetAccessControls and in the Docker-label fallback (GetLabels), while nginx, Traefik, and Caddy route hostnames case-insensitively; requesting the target app with a differently-cased hostname therefore misses the configured policy, returns an empty access-control object, and proxyHandler treats the empty user/group/OAuth/LDAP/IP restrictions as permissive. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Requires ALL of the following: (1) Tinyauth prior to 5.1.2 deployed as a forward-auth/authorization server behind a reverse proxy that routes hostnames case-insensitively (typical of nginx/Traefik/Caddy); (2) per-app access controls configured either via static domain ACLs (lookupStaticACLs/GetAccessControls) or the Docker-label fallback (GetLabels); (3) an access-control policy that is meant to EXCLUDE the attacker from at least one app; and (4) the attacker holds valid low-privilege authenticated credentials (PR:L). … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The vendor CVSS 3.1 vector (AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N, base 8.1) describes a network-reachable, low-complexity flaw requiring only low-privilege authentication and no user interaction - a plausible score for an authorization bypass that grants access to protected applications. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | Full exploit scenario with step-by-step reproduction available after sign-in. |
| Remediation | Vendor-released patch: upgrade to Tinyauth 5.1.2 (https://github.com/tinyauthapp/tinyauth/releases/tag/v5.1.2), which is the only version that carries the new pkg/validators/domain_validator.go normalization logic; the underlying fixes are visible in pull requests https://github.com/tinyauthapp/tinyauth/pull/1000 and https://github.com/tinyauthapp/tinyauth/pull/1028 and commits 80bc87188ec3aabc5104c249eaa7b997973b9275 and e75605b2c534ec83525a33603e16d76baca13399. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours, identify every Tinyauth deployment that enforces per-application ACLs behind nginx, Traefik, or Caddy, and treat those instances as unenforced until remediated; upgrade to Tinyauth 5.1.2 as the vendor-released fix, and where an immediate upgrade is not possible, normalize or lowercase the forwarded hostname at the proxy layer (rewrite/reject mixed-case Host headers) so lookups match configured policy, and briefly review access logs for mixed-case Host headers against protected applications. …
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Same weakness CWE-178 – Improper Handling of Case Sensitivity
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