GHSA-cmwh-g2h8-c222

GHSA-cmwh-g2h8-c222 · Poweradmin: OIDC `sub` collation bypass in Poweradmin leading to account takeover

This page contains facts from public vulnerability sources. Check the original advisory before updating.

This page shows selected source facts. See the linked advisories for the complete description and affected versions.

## Preface Poweradmin maps OIDC identities into local users through `oidc_user_links.oidc_subject` plus `provider_id`. In the MySQL schema, the OIDC link table explicitly uses `utf8mb4_unicode_ci`, which is case-insensitive and accent-insensitive. OIDC `sub` is a stable external subject identifier and should be matched byte-for-byte within the issuer/provider scope. The confirmed local PoC used two different OIDC users: - Victim subject: `victim-login` - Attacker subject: `victím-login` (`í`, U+00ED) MySQL reported those two subjects as equal under `utf8mb4_unicode_ci`. After the victim linked their OIDC account, the attacker authenticated to the same provider with the attacker's own password and Poweradmin resolved the session to the victim's local account. ## Server Info - **Application:** Poweradmin - **Version:** `targets/poweradmin` git `e1f9c9a` - **Database:** MySQL `8.4.10`, `character_set_server=utf8mb4`, `collation_server=utf8mb4_unicode_ci` - **Access Permissions:** Any user who can create or control an account in the connected OIDC provider - **Auth Method:** OIDC generic provider - **Tools:** Docker Compose, local OIDC provider, Python PoC harness **Affected Entry Point:** ```text GET /oidc/login?provider=generic GET /oidc/callback?code=...&state=... ``` Relevant request properties: - Authentication: valid OIDC authorization code flow - Trigger: attacker OIDC account has a `sub` that collides with a victim's linked `sub` - Vulnerable field: OIDC `sub` stored and looked up as `oidc_user_links.oidc_subject` ## Root Cause Analysis ### part0 — `oidc_user_links.oidc_subject` uses an accent-insensitive collation The MySQL schema defines the OIDC link table with `utf8mb4_unicode_ci`: ```sql -- sql/poweradmin-mysql-db-structure.sql:341-356 CREATE TABLE `oidc_user_links` ( `user_id` INT(11) NOT NULL, `provider_id` VARCHAR(50) NOT NULL, `oidc_subject` VARCHAR(255) NOT NULL, ... UNIQUE KEY `unique_subject_provider` (`oidc_subject`, `provider_id`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci; ``` In the PoC database: ```text Field Type Collation provider_id varchar(50) utf8mb4_unicode_ci oidc_subject varchar(255) utf8mb4_unicode_ci SELECT 'victim-login' = 'victím-login' COLLATE utf8mb4_unicode_ci; -- accent_collision = 1 ``` ### part1 — OIDC `sub` flows into a normal SQL equality lookup Poweradmin reads the subject from OIDC userinfo data. If no custom `subject` mapping is configured, it uses the `sub` claim: ```php // lib/Application/Service/OidcService.php:424-459 $resourceOwner = $provider->getResourceOwner($token); $userData = $resourceOwner->toArray(); ... subject: $userData[$mapping['subject'] ?? 'sub'] ?? '', ``` The callback passes the resulting `OidcUserInfo` to provisioning: ```php // lib/Application/Service/OidcService.php:269-291 $userInfo = $this->getUserInfo($provider, $token, $providerId); $userId = $this->userProvisioningService->provisionUser($userInfo, $providerId); ``` Provisioning first tries to find an existing user by subject: ```php // lib/Application/Service/UserProvisioningService.php:86-90 $existingUserId = $authMethod === self::AUTH_METHOD_SAML ? $this->findUserBySamlSubject($userInfo->getSubject(), $providerId) : $this->findUserByOidcSubject($userInfo->getSubject(), $providerId); ``` The lookup is normal SQL equality evaluated under the column's weak collation: ```php // lib/Application/Service/UserProvisioningService.php:145-149 $stmt = $this->db->prepare(" SELECT user_id FROM oidc_user_links WHERE oidc_subject = ? AND provider_id = ? "); $stmt->execute([$subject, $providerId]); ``` When the attacker authenticates with `sub = victím-login`, MySQL matches the existing row for `oidc_subject = victim-login` and returns the victim's `user_id`. ### part2 — The returned user ID becomes the authenticated session After provisioning returns the matched `user_id`, Poweradmin fetches the database username for that user and stores the matched user ID in the session: ```php // lib/Application/Service/OidcService.php:307-317 $databaseUsername = $this->userProvisioningService->getDatabaseUsername($userId); $this->setSessionValue('userlogin', $databaseUsername); ``` ```php // lib/Application/Service/OidcService.php:360-371 $this->setSessionValue('userid', $userId); ... $this->setSessionValue('authenticated', true); ``` The attacker's OIDC password is validated by the IdP, but the local `user_id` selected by Poweradmin comes from the weak-collation SQL lookup. ## Security Impact An attacker who can register or control an OIDC principal with an accent/collation variant of a victim's OIDC subject can authenticate with the attacker's own IdP credentials and obtain a Poweradmin session for the victim's local account. The confirmed PoC used distinct OIDC usernames, subjects, emails, and passwords. The attacker did not know or modify the victim's password. ## Reproduction ### 1. Start the local Poweradmin OIDC lab ```bash sudo -n docker compose -p poweradminoidcpoc -f poc/work/poweradmin-oidc-collation/docker-compose.yml up -d ``` The lab uses MySQL `utf8mb4_unicode_ci` and a local OIDC provider with two real login accounts: ```text Victim: username/sub: victim-login email: [email protected] password: VictimPassword123! Attacker: username/sub: victím-login email: [email protected] password: AttackerPassword123! ``` ### 2. Log in once as the victim through OIDC Authenticate through `GET /oidc/login?provider=generic` using: ```text username: victim-login password: VictimPassword123! ``` Poweradmin creates the victim local user and OIDC link: ```text users: id username fullname email 2 victim-login Victim Poweradmin [email protected] oidc_user_links: id user_id provider_id oidc_subject 1 2 generic victim-login ``` ### 3. Log in as the attacker OIDC user Authenticate from a separate browser session with: ```text username: victím-login password: AttackerPassword123! ``` Observed result from `poc/work/poweradmin-oidc-collation/run_poc.py`: ```json { "attacker_login": { "selected_idp_user": "attacker", "selected_idp_username": "victím-login", "has_session_cookie": true, "home_contains_victim_username": true, "home_contains_attacker_username": false }, "attacker_resolved_to_victim": true } ``` Database evidence after both logins: ```text version charset_server collation_server 8.4.10 utf8mb4 utf8mb4_unicode_ci accent_collision 1 users: id username fullname email 2 victim-login Victim Poweradmin [email protected] oidc_user_links: id user_id provider_id oidc_subject oidc_subject_hex 1 2 generic victim-login 76696374696D2D6C6F67696E ``` The application audit log also records all OIDC login events as the victim user: ```text user:victim-login operation:login_success auth_method:oidc ``` No local user or OIDC link was created for `victím-login`. ## Recommended Fix Treat OIDC subject identifiers as byte-exact strings. For MySQL, migrate the OIDC mapping identifiers to a binary or byte-preserving collation: ```sql ALTER TABLE oidc_user_links MODIFY COLUMN provider_id varchar(50) CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NOT NULL, MODIFY COLUMN oidc_subject varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NOT NULL; ``` Also make lookup queries byte-preserving so patched application code protects existing deployments before schema migrations are complete: ```php $stmt = $this->db->prepare(" SELECT user_id FROM oidc_user_links WHERE BINARY oidc_subject = BINARY ? AND BINARY provider_id = BINARY ? "); ``` Review related identity and authorization lookups: - `findUserByEmail()` uses `users.email = ?` and can be impacted when `link_by_email` is enabled. - `findPermissionTemplateByName()` uses `perm_templ.name = ?`

CVSS 8.1 · High · Fix available

Published

2026-07-24T21:56:02Z

Updated

2026-07-24T22:00:26.986671227Z

Stack: php

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