Siemens Mendix SAML prior 4.2.4/3.6.29 authentication replay

Summaryinfo

A vulnerability classified as critical has been found in Siemens Mendix SAML. Affected by this issue is some unknown functionality. The manipulation leads to authentication replay. This vulnerability is listed as CVE-2026-89209. The attack may be initiated remotely. There is no available exploit. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability was found in Siemens Mendix SAML. It has been rated as critical. This issue affects some unknown processing. The manipulation with an unknown input leads to a authentication replay vulnerability. Using CWE to declare the problem leads to CWE-294. A capture-replay flaw exists when the design of the product makes it possible for a malicious user to sniff network traffic and bypass authentication by replaying it to the server in question to the same effect as the original message (or with minor changes). Impacted is confidentiality, integrity, and availability. The summary by CVE is:

A vulnerability has been identified in Mendix SAML (Mendix 10 compatible) (All versions < V4.2.4), Mendix SAML (Mendix 11 compatible) (All versions < V4.2.4), Mendix SAML (Mendix 9 compatible) (All versions < V3.6.29). Affected versions of the module do not properly protect against SAML assertion replay in IdP-initiated authentication flows. This could allow unauthenticated remote attackers to gain unauthorized access to the application by replaying a valid SAML response.

It is possible to read the advisory at cert-portal.siemens.com. The identification of this vulnerability is CVE-2026-89209 since 09/11/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. The technical details are unknown and an exploit is not publicly available. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 10/26/2026). The attack technique deployed by this issue is T1040 according to MITRE ATT&CK.

Upgrading to version 4.2.4 or 3.6.29 eliminates this vulnerability.

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Productinfo

Vendor

• Siemens

Name

• Mendix SAML

License

• commercial

Website

• Vendor: https://www.siemens.com/

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