Siemens Mendix SAML Authentication Bypass: What DoD STIG Teams Must Do Now
CISA Advisory ICSA-26-302-01 flags a replay-attack vulnerability in Mendix SAML modules — here's the 30-day action plan for STIG-aligned environments.
Published 2026-10-29
# Siemens Mendix SAML Authentication Bypass: What DoD STIG Teams Must Do Now
CISA advisory ICSA-26-302-01 discloses an authentication bypass vulnerability in the Siemens Mendix SAML module that could allow an unauthenticated remote attacker to hijack sessions by replaying a previously captured SAML assertion — no credentials required.
What the Advisory Actually Says
The vulnerability affects the Mendix SAML module across three compatibility tracks: Mendix 9 (versions below 3.6.29), Mendix 10 (versions below 4.2.4), and Mendix 11 (versions below 4.2.4). The root cause is inadequate protection against assertion replay in IdP-initiated authentication flows. In plain terms: if an attacker can intercept or obtain a valid SAML token — even a recently expired one — they may be able to reuse it to authenticate as a legitimate user without ever touching a password. Siemens has released patched versions and recommends immediate upgrade. CISA rates the vulnerability at CVSS v3 6.8 and flags deployment sectors as Critical Manufacturing and Information Technology worldwide.
Why This Is a High-Priority STIG Concern
For teams operating under DoD STIG controls, SAML-based single sign-on is a common identity federation path for enterprise low-side and some enclave applications built on Mendix. A replay-capable authentication bypass maps directly to STIG control families around identification and authentication (IA) and session management, and it will surface as a finding in any honest ACAS (Assured Compliance Assessment Solution) scan or SCAP benchmark evaluation.
The CVSS score of 6.8 places this in the medium-high band, but context elevates the real risk considerably. In DoD environments, unauthorized access through a federated identity path can propagate laterally across enclaves, defeat audit-trail integrity, and trigger mandatory reporting under the DoD Cyber Incident Reporting requirements. Leaving this unpatched beyond the next ACAS scan cycle is not a defensible position for an authorizing official or ISSO.
Beyond DoD, organizations in EU critical infrastructure or those aligning to NIS2 should note that CISA explicitly flags worldwide deployment — meaning this vulnerability is active across multiple regulatory jurisdictions simultaneously.
Your 7–30 Day Response Checklist
Within 7 days:
- Audit every Mendix deployment in your environment and confirm the exact module version in use for each compatibility track (Mendix 9, 10, 11).
- Prioritize any instance that uses IdP-initiated SAML flows — these are the directly exploitable configurations described in the advisory.
- Open change-management tickets to schedule patching to Mendix SAML 3.6.29 (Mendix 9) or 4.2.4 (Mendix 10/11).
Within 14 days:
- Apply vendor-released patches and validate in a staging environment before production push.
- Update your ACAS/SCAP plugin inventory to ensure the patched versions are recognized as compliant in your next scheduled scan.
- Review STIG IA control findings in your existing POA&M and link this advisory as supporting evidence for any open authentication-related items.
Within 30 days:
- Conduct a post-patch ACAS scan and document closure of related findings.
- Brief your AO or ISSO with evidence of remediation for RMF continuous monitoring records.
- If your environment includes NIS2-regulated entities, document the advisory response in your incident and vulnerability management log as required under Article 21 technical measures.
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