Admidio — CraftedSignal Threat Feed

Admidio SAML Signature Validation Bypass Allows Forged AuthnRequests and LogoutRequests

hello@craftedsignal.io — Wed, 29 Apr 2026 21:56:13 +0000

Admidio, a free web-based content management system for organizations and groups, contains a critical vulnerability in its SAML Single Sign-On (SSO) implementation. The validateSignature() method within the SAMLService class returns error strings upon signature validation failure, rather than throwing exceptions. The calling functions, handleSSORequest() and handleSLORequest(), incorrectly assume that the method throws an exception, and therefore, do not check the return value. This oversight renders the smc_require_auth_signed configuration option ineffective, allowing attackers to forge SAML AuthnRequests and LogoutRequests. An attacker can exploit this vulnerability to obtain sensitive user information or cause denial of service by terminating user sessions. This affects Admidio versions 5.0.8 and earlier and requires SAML SSO to be enabled.

Attack Chain

An attacker crafts a malicious SAML AuthnRequest or LogoutRequest without a valid signature, impersonating a legitimate Service Provider (SP).
The attacker sends the forged SAML request to the Admidio instance via HTTP GET or POST to modules/sso/index.php.
The receiveMessage() function parses the SAML binding directly from the HTTP request, requiring no prior authentication.
The Entity ID is extracted from the forged request’s Issuer element, and the corresponding client configuration is loaded.
The validateSignature() function is called, but its return value (indicating signature validity) is discarded.
For AuthnRequests, if the targeted user has an active session ($gValidLogin is true), the login form is skipped.
Admidio builds a SAML Response containing the user’s attributes (login, name, email, roles) and sends it to the attacker-controlled AssertionConsumerServiceURL.
For LogoutRequests, the user’s session is immediately terminated in the database, triggering a cascading single logout across all registered SPs.

Impact

Successful exploitation of this vulnerability can lead to several critical impacts. The primary impact is the complete bypass of signature enforcement, negating the security benefits of the smc_require_auth_signed setting. This can lead to the disclosure of sensitive user attributes, including login name, email, and role memberships, to unauthorized parties by forging SSO requests and redirecting them to attacker-controlled endpoints. Furthermore, attackers can terminate any user’s Admidio session by forging SLO requests, potentially causing a denial-of-service condition. This vulnerability affects all Admidio instances with SAML SSO enabled and can potentially impact all users of the system.

Recommendation

Apply the recommended fix in the Admidio codebase to check the return value of validateSignature() and throw an exception on failure, as outlined in the advisory (https://github.com/advisories/GHSA-25cw-98hg-g3cg).
Deploy the Sigma rule “Admidio Forged SAML AuthnRequest Detection” to detect potentially malicious SAML AuthnRequests lacking a valid signature via webserver logs.
Deploy the Sigma rule “Admidio Forged SAML LogoutRequest Detection” to detect potentially malicious SAML LogoutRequests lacking a valid signature via webserver logs.
Monitor webserver logs for requests to /adm_program/modules/sso/index.php/saml/sso and /adm_program/modules/sso/index.php/saml/slo without proper signature validation to detect potential exploitation attempts.
Upgrade to a patched version of Admidio to address CVE-2026-41669.

Admidio SAML Assertion Consumer Service (ACS) URL Validation Bypass

hello@craftedsignal.io — Mon, 29 Jan 2024 12:00:00 +0000

A vulnerability exists in Admidio’s SAML IdP implementation within the SSO module (versions 5.0.8 and earlier) that allows for bypassing Assertion Consumer Service (ACS) URL validation. The IdP uses the AssertionConsumerServiceURL value directly from incoming SAML AuthnRequest messages as the destination for the SAML response without verifying it against the registered smc_acs_url for the corresponding service provider client. An attacker can exploit this by crafting a SAML AuthnRequest with the Entity ID of a registered SP client and an attacker-controlled AssertionConsumerServiceURL. This causes the IdP to send the signed SAML response, containing sensitive user identity attributes (login name, email, roles, profile fields), to a URL controlled by the attacker. The default configuration does not require signed AuthnRequests, simplifying exploitation to only needing the SP’s Entity ID.

Attack Chain

The attacker identifies the Entity ID of a registered SAML service provider (SP) client within the Admidio IdP. This is often publicly available from the SP’s metadata endpoint.
The attacker crafts a malicious SAML AuthnRequest. The AuthnRequest includes the legitimate SP Entity ID as the Issuer, but sets the AssertionConsumerServiceURL to a URL controlled by the attacker (e.g., https://attacker.test/steal-saml).
The attacker sends the crafted SAML AuthnRequest to Admidio’s SSO endpoint (/modules/sso/index.php/saml/sso) using the HTTP-POST binding, typically by tricking a logged-in user into accessing a webpage containing an auto-submitting form.
Admidio’s SSO module receives the AuthnRequest. If signature validation is not enforced for the SP, the request proceeds without signature verification.
If the user is already authenticated with the Admidio IdP, the IdP generates a signed SAML response containing the user’s identity and attributes. The destination of the SAML response is set to the attacker-controlled AssertionConsumerServiceURL taken directly from the AuthnRequest.
Admidio renders an auto-submitting HTML form in the victim’s browser, which POSTs the signed SAML response to the attacker’s URL (https://attacker.test/steal-saml).
The attacker’s server receives the SAML response, extracting the user’s login name, email, full name, roles, and any other profile fields included in the assertion.
The attacker replays the stolen SAML assertion to the legitimate SP to authenticate as the victim, gaining unauthorized access to the SP application and its resources.

Impact

Successful exploitation of this vulnerability allows an attacker to steal user identities and impersonate victims on legitimate service provider applications. This leads to unauthorized access to user accounts and potential access to sensitive data and resources within those applications. The scope change enables impersonation across separate service provider applications. The vulnerability is exploitable without requiring knowledge of cryptographic keys if smc_require_auth_signed is not enabled, making it easier to exploit. All versions of Admidio up to and including 5.0.8 are affected.

Recommendation

Apply the vendor-supplied patch described in GHSA-p9w9-87c8-m235 by upgrading to a version of Admidio greater than 5.0.8.
As a temporary mitigation, enable smc_require_auth_signed and smc_validate_signatures for all SAML clients to enforce signature validation, mitigating attacks from unauthenticated sources.
Monitor web server logs for POST requests to the Admidio SSO endpoint (/modules/sso/index.php/saml/sso) with suspicious SAMLRequest parameters containing attacker-controlled AssertionConsumerServiceURL values, which can be detected using the “Admidio SAML AuthnRequest ACS URL Override” Sigma rule.
Monitor network traffic for connections to attacker-controlled URLs, such as https://attacker.test/steal-saml, which may indicate successful exploitation and the exfiltration of SAML responses as listed in the IOC table.

Admidio Inverted 2FA Reset Allows Privilege Escalation

hello@craftedsignal.io — Mon, 22 Jan 2024 12:00:00 +0000

Admidio, a web-based content management system for organizations, contains a critical vulnerability in its two-factor authentication (2FA) reset mechanism. The vulnerability, present in versions 5.0.8 and earlier, stems from an inverted authorization check within the modules/profile/two_factor_authentication.php script. This flaw enables non-administrative users, specifically group leaders with profile edit rights, to disable 2FA for other users, including administrator accounts. The vulnerability was reported on April 29, 2026. By exploiting this flaw, attackers can bypass 2FA, gaining unauthorized access to privileged accounts and potentially compromising the entire Admidio installation. This highlights the importance of rigorous security audits and proper authorization checks in web applications.

Attack Chain

An attacker compromises or gains access to a non-admin user account within Admidio that possesses hasRightEditProfile() permission over an administrator account.
The attacker crafts a POST request to /adm_program/modules/profile/two_factor_authentication.php with the mode parameter set to reset and the user_uuid parameter set to the UUID of the target administrator account.
The server-side script modules/profile/two_factor_authentication.php executes the flawed authorization check at line 84. Due to the inverted logic (!== instead of ===), the check incorrectly grants permission to the non-admin user to reset the administrator’s 2FA.
The server removes the TOTP configuration associated with the administrator’s account from the database or configuration files.
The attacker can now attempt to log in to the administrator account using only the password, bypassing the 2FA requirement.
If the attacker knows or can guess the administrator’s password (via credential stuffing, brute force, or other means), they successfully gain access to the account.
With administrator privileges, the attacker can perform a variety of malicious actions, such as creating new accounts, modifying website content, or accessing sensitive data.

Impact

The vulnerability allows attackers to bypass two-factor authentication on administrator accounts in Admidio installations. This can lead to unauthorized access to sensitive data, modification of website content, and potentially full control over the affected system. While the number of affected installations is unknown, organizations using vulnerable versions of Admidio are at risk. Success of the attack results in complete compromise of the Admidio instance and the data it manages.

Recommendation

Apply the recommended fix by changing !== to === on line 84 of modules/profile/two_factor_authentication.php to correct the authorization logic (see Overview).
Deploy the Sigma rule Detect Admidio 2FA Reset Request to detect attempts to exploit this vulnerability by monitoring HTTP POST requests to the vulnerable endpoint (see Rules).
Upgrade Admidio to a patched version that incorporates the fix for CVE-2026-41660.