The recent disclosure of a security vulnerability in Siemens’ Mendix OIDC SSO modules has sent ripples across industries that rely on low-code platforms for rapid digital transformation, especially where secure authentication is paramount. Siemens—a global leader in industrial automation, healthcare, and infrastructure—has traditionally enjoyed a reputation for robust, trustworthy products. Yet this latest advisory, identified as CVE-2025-40571, highlights an all-too-familiar challenge: even marquee software components can harbor subtle flaws with wide-reaching implications.
Mendix, acquired by Siemens in recent years, is a leading low-code platform designed to accelerate application development across sectors ranging from manufacturing to finance and healthcare. Integral to Mendix’s offering is the ability to authenticate users via modern, standards-based protocols—chief among them OpenID Connect (OIDC) Single Sign-On (SSO). The OIDC SSO module enables seamless integration with external identity providers, streamlining both user and administrator experiences while purportedly maintaining strict role-based access controls.
The incident at hand centers on how the OIDC SSO module implements and enforces these access controls. Specifically, the Mendix OIDC SSO modules compatible with Mendix 9 (all versions) and Mendix 10 (all versions before v4.0.0) have been found vulnerable due to incorrect privilege assignment within their token handling subsystems. In essence, a flaw in privilege configuration could allow users with the ability to modify the module—typically developers or administrators—to grant themselves or others unauthorized administrative read/write rights over OIDC tokens. While seemingly subtle, the consequences can be profound, especially in heavily regulated or mission-critical environments.
It’s essential to remember, however, that in industrial, healthcare, and critical infrastructure environments—where Mendix is widely deployed—privilege misassignments can have cascading, real-world impacts. Unauthorized access to authentication tokens can mean anything from sensitive data leakage to disruption of vital digital processes or even compromise of physical assets, depending on integration scope.
Of note, since January 2023, CISA has ceased ongoing updates to ICS advisories after their initial publication, instead directing users to vendor-maintained CERT portals for the latest details. For Siemens customers, this means regular consultation of Siemens’ ProductCERT security advisories is now a necessity for maintaining strong security hygiene.
Furthermore, the CVSS scores and vector data have been transparently shared, allowing technical teams to prioritize risk based on environment context. The relatively low base score is explained not as a sign of insignificance, but as a function of the exploit’s dependence on authorized access or insider threat—a subtle but important distinction, especially for decision-makers prioritizing vulnerability management and patch cycles.
The cloud-first transformation in all these sectors also means that vulnerabilities in identity modules—especially those enabling SSO—are high-value targets for attackers. As “zero trust” paradigms become the norm, confirmation of least privilege across the development and runtime environments gains urgency.
Modern SSO implementations (OIDC and SAML alike) are foundational to digital trust. When privilege assignment across these solutions is weak or ambiguous, the entire edifice of secure authentication is at risk. This incident joins a growing list of vulnerabilities where the “human factors” of configuration and access management are as vital as technical countermeasures. As enterprise development practices become more democratized—with business users, citizen developers, and IT professionals collaborating on virtual platforms—security teams must redouble efforts to bake security into every step of the application development life cycle.
As critical infrastructure, healthcare, and financial providers accelerate digital transformation, the guardrails around identity management modules must become more stringent, not less. Vulnerabilities stemming from incorrect privilege assignment will continue to surface, especially in platforms that straddle IT and OT domains.
The lesson for forward-looking organizations is clear: the path to secure digital transformation is paved not only with patches and configuration changes, but with a fundamental commitment to rigorous privilege management, continuous monitoring, and a culture of shared responsibility for digital trust—across every stage and every stakeholder in the software development life cycle.
For Siemens Mendix users and the global security community alike, the call is for vigilance, agility, and a relentless focus on “defending identity” as the core of modern enterprise resilience.
Source: CISA Siemens Mendix OIDC SSO | CISA
Mendix, acquired by Siemens in recent years, is a leading low-code platform designed to accelerate application development across sectors ranging from manufacturing to finance and healthcare. Integral to Mendix’s offering is the ability to authenticate users via modern, standards-based protocols—chief among them OpenID Connect (OIDC) Single Sign-On (SSO). The OIDC SSO module enables seamless integration with external identity providers, streamlining both user and administrator experiences while purportedly maintaining strict role-based access controls.The incident at hand centers on how the OIDC SSO module implements and enforces these access controls. Specifically, the Mendix OIDC SSO modules compatible with Mendix 9 (all versions) and Mendix 10 (all versions before v4.0.0) have been found vulnerable due to incorrect privilege assignment within their token handling subsystems. In essence, a flaw in privilege configuration could allow users with the ability to modify the module—typically developers or administrators—to grant themselves or others unauthorized administrative read/write rights over OIDC tokens. While seemingly subtle, the consequences can be profound, especially in heavily regulated or mission-critical environments.
Breaking Down CVE-2025-40571: Flaw Summary and Technical Context
What Went Wrong?
The vulnerability, tracked as CVE-2025-40571, arises due to incorrect privilege assignment (CWE-266). In the affected Mendix OIDC SSO modules, the OIDC.Token entity is configured such that read and write access is by default granted to the Administrator role. The key risk is that an adversary with development-level access—either through legitimate credentials that are later abused, or through a compromised developer account—can modify this module during the Mendix application development lifecycle. Once altered, the attacker may escalate their privileges or those of a collaborator, gaining access to sensitive authentication tokens and thus the potential to subvert the application’s entire identity system.Risk Assessment: Remote Exploitability, Attack Complexity, and Severity
The vulnerability is potentially exploitable remotely, though the overall CVSS score (2.1 under v4.0, 2.2 under v3.1) may appear low at first glance. This is principally due to its high attack complexity: a would-be attacker must already possess some privileged role or subvert the development workflow itself. The default configuration acts as a barrier, but not an insurmountable one—especially in collaborative or poorly audited Mendix environments. The root issue is not direct external exploitability, but the possibility of internal misuse, accidental exposure, or supply-chain style attacks where development processes serve as an attack vector.It’s essential to remember, however, that in industrial, healthcare, and critical infrastructure environments—where Mendix is widely deployed—privilege misassignments can have cascading, real-world impacts. Unauthorized access to authentication tokens can mean anything from sensitive data leakage to disruption of vital digital processes or even compromise of physical assets, depending on integration scope.
Affected Products and Software Scope
- Siemens Mendix OIDC SSO (Mendix 9 Compatible): All versions are affected; as of this writing, no fix is available.
- Siemens Mendix OIDC SSO (Mendix 10 Compatible): All versions prior to v4.0.0 are vulnerable. Users are urged to upgrade to v4.0.0 or newer via the Mendix Marketplace.
Vulnerability Disclosure and Response: Siemens and CISA
The vulnerability was self-reported by Siemens ProductCERT—reflecting the company’s proactive approach to product security—and registered with the Cybersecurity and Infrastructure Security Agency (CISA) in the United States. CISA’s advisory (ICSA-25-135-15) echoes Siemens’ recommendations and reinforces standard best practices for asset isolation and access control.Of note, since January 2023, CISA has ceased ongoing updates to ICS advisories after their initial publication, instead directing users to vendor-maintained CERT portals for the latest details. For Siemens customers, this means regular consultation of Siemens’ ProductCERT security advisories is now a necessity for maintaining strong security hygiene.
Mitigation Guidance: What Users Should Do Next
Official Recommendations from Siemens
Siemens offers a tiered mitigation strategy:- All Users: By default, OIDC.Token entity access is limited to the Administrator role. Organizations should immediately review whether this default is sufficiently restrictive, and if warranted, tighten access further by redefining access rules or creating differentiated user roles.
- Mendix 10 OIDC SSO Users: Upgrade affected module versions to 4.0.0 or higher via Mendix Marketplace.
- Mendix 9 OIDC SSO Users: No direct fix is available. Organizations must implement recommended access control changes and increase monitoring for possible privilege escalation within the module.
- All Environments: Secure network access to Mendix development workflows and OIDC SSO-integrated environments. This entails robust segmentation, firewalling, and, where appropriate, network isolation according to Siemens’ operational security guidelines.
Broader Defensive Controls by CISA
CISA reinforces several crucial operational recommendations:- Minimize exposure: Ensure control system nodes and authentication modules are never directly accessible from the Internet.
- Segmentation: Keep control system networks (including Mendix environments) behind dedicated firewalls, separate from business networks, reducing lateral movement possibilities in case of compromise.
- Secure remote access: If remote administration is necessary, restrict it to tightly controlled VPNs, ensure these VPNs are updated, and recognize that VPNs themselves are not a panacea—endpoint hygiene is critical.
- Incident readiness: Maintain up-to-date incident response plans, including processes for internal reporting and regular risk assessment to quantify potential business impact before deploying defensive measures.
Critical Analysis: Strengths, Weaknesses, and Industry Implications
Strengths and Remediations
Siemens’ coordination with CISA and public disclosure of the issue demonstrate a mature approach to security, especially in the context of industrial control systems, where “security through obscurity” has too often reigned. The company’s clear mitigation advice—including explicit patching for Mendix 10 users and compensating controls for Mendix 9—reflects an understanding of the real-world complexities customers face. The recognition that no “one size fits all” solution exists, and the encouragement for granular access rule tailoring, also exemplifies best practice.Furthermore, the CVSS scores and vector data have been transparently shared, allowing technical teams to prioritize risk based on environment context. The relatively low base score is explained not as a sign of insignificance, but as a function of the exploit’s dependence on authorized access or insider threat—a subtle but important distinction, especially for decision-makers prioritizing vulnerability management and patch cycles.
Weaknesses and Ongoing Risks
However, significant limitations and residual risks remain:- No Patch for Mendix 9: The lack of a direct fix for Mendix 9 compatible modules is troubling. Despite guidance on configuration hardening, organizations running Mendix 9 are in the difficult position of relying solely on compensating controls and process discipline. Resource-stretched teams or those with legacy applications may struggle to implement and maintain these controls consistently.
- Potential for Insider Abuse: The exploit pathway is not trivial, but neither is it prohibitively complicated for a determined adversary already inside the organization’s developer or administrator ranks. Incorrect trust boundaries in the software development process remain a perennial Achilles' heel for enterprise security.
- Complexity of Mendix Deployments: Many Mendix user organizations deliver rapid-fire applications often managed by cross-functional teams. The interplay between “low-code” promises and secure SDLC practices is not always seamless—providing more ways for misconfiguration or unintentional privilege creep.
- Supply Chain Considerations: In environments where application modules or solution accelerators are shared between organizations, the privilege assignment issue could propagate, amplifying risk well beyond one enterprise.
Real-World Implications Across Sectors
In critical manufacturing, healthcare, and energy—verticals explicitly called out in the Siemens/CISA alert—the stakes for privilege mismanagement are unusually high. A compromised authentication authority can disrupt operational technology, block access to vital information, or serve as a hop-point in broader campaigns against industrial or healthcare targets. In regulated finance environments, the privacy, auditability, and immutability of authentication operations are tightly scrutinized, making timely patching and proactive defense a board-level concern.The cloud-first transformation in all these sectors also means that vulnerabilities in identity modules—especially those enabling SSO—are high-value targets for attackers. As “zero trust” paradigms become the norm, confirmation of least privilege across the development and runtime environments gains urgency.
Lessons Learned: The Broader Context of Identity and Privilege Security
CVE-2025-40571 is not a remote code execution bug or an “Internet worm” vulnerability. Yet it deserves attention precisely because of what it reveals about the evolving security threats facing cloud-enabled, low-code development environments in critical infrastructure. The bug’s existence points to the enduring challenge of enforcing the principle of least privilege—not just in application runtime roles, but across the development workflow itself.Modern SSO implementations (OIDC and SAML alike) are foundational to digital trust. When privilege assignment across these solutions is weak or ambiguous, the entire edifice of secure authentication is at risk. This incident joins a growing list of vulnerabilities where the “human factors” of configuration and access management are as vital as technical countermeasures. As enterprise development practices become more democratized—with business users, citizen developers, and IT professionals collaborating on virtual platforms—security teams must redouble efforts to bake security into every step of the application development life cycle.
Recommendations for Siemens Mendix Customers
From a pragmatic perspective, Mendix users and security administrators should move quickly and decisively:- Inventory and Assess: Immediately identify Mendix deployments using the affected versions of OIDC SSO modules. Catalog any environments running Mendix 9, as these will require the most urgent compensating controls.
- Implement Stronger Access Rule Hardening: Revisit the OIDC.Token entity configuration. Restrict read/write access to the smallest possible set of roles. If custom roles are necessary, ensure their permissions are comprehensively understood and documented.
- Patch and Upgrade: For Mendix 10 environments, upgrade the OIDC SSO module to version 4.0.0 or newer. Monitor the Mendix Marketplace and Siemens ProductCERT advisory pages for additional updates or security patches as they are released.
- Harden Development Workflows: Audit who can modify OIDC SSO modules, both in production and in development. Treat “development environment” access with the same trust boundaries as production, especially for modules that control authentication or authorization.
- Review Segmentation and Incident Response: Confirm network segmentation and incident detection controls cover Mendix-related assets and administrative workflows. Ensure security monitoring includes events related to privilege changes in these modules.
- Foster a Security-First Culture: Train business and IT staff on the importance of least privilege across both application roles and software development processes. Encourage the reporting of suspicious privilege escalations or unusual module modifications.
The Road Ahead: Embracing Zero Trust and Secure Low-Code Practices
The Siemens Mendix OIDC SSO vulnerability may ultimately be remembered as a relatively low-severity flaw with limited exploitability “in the wild.” However, it underscores a pattern of escalating sophistication in threats targeting authentication infrastructure—particularly where legacy development models intersect with cloud and low-code technologies.As critical infrastructure, healthcare, and financial providers accelerate digital transformation, the guardrails around identity management modules must become more stringent, not less. Vulnerabilities stemming from incorrect privilege assignment will continue to surface, especially in platforms that straddle IT and OT domains.
The lesson for forward-looking organizations is clear: the path to secure digital transformation is paved not only with patches and configuration changes, but with a fundamental commitment to rigorous privilege management, continuous monitoring, and a culture of shared responsibility for digital trust—across every stage and every stakeholder in the software development life cycle.
For Siemens Mendix users and the global security community alike, the call is for vigilance, agility, and a relentless focus on “defending identity” as the core of modern enterprise resilience.
Source: CISA Siemens Mendix OIDC SSO | CISA