CVE-2026-28390 Siemens CVE debrief

Who should care

Security teams and operators who run applications, gateways, or services that process untrusted CMS/S-MIME data; defenders responsible for Siemens advisory intake; and teams that embed CMS_decrypt()-style workflows in exposed services.

Technical summary

The issue is a NULL pointer dereference during CMS EnvelopedData processing when KeyTransportRecipientInfo is used with RSA-OAEP encryption and the optional parameters field of the RSA-OAEP algorithm identifier is not present. Because the faulty path is reachable through attacker-controlled CMS data, the result is a crash/DoS rather than a confidentiality or integrity break. The source corpus gives a CVSS 3.1 vector of AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H (7.5 HIGH).

Defensive priority

High. Prioritize if your environment accepts CMS or S/MIME content from untrusted sources or exposes CMS_decrypt() functionality over a network or through semi-trusted workflows. Availability impact can be immediate and requires only crafted input.

Recommended defensive actions

• Apply the vendor fix: update to V5.0 or later for the affected Siemens product listed in the advisory.
• Inventory any services or applications that process CMS EnvelopedData, S/MIME, or other CMS-based protocols from untrusted sources.
• Treat malformed or attacker-controlled CMS inputs as untrusted and place parsing paths behind strict input validation and layered isolation where possible.
• Verify whether your deployment uses only the unaffected OpenSSL FIPS module boundary components; the advisory states the FIPS modules listed are not affected.
• Monitor for crashes or abnormal terminations in CMS-processing components and add alerting around repeated parse failures.

Evidence notes

All claims above are drawn from the provided CISA CSAF source item and its referenced Siemens/CISA advisory material. The source item identifies CVE-2026-28390, describes the NULL pointer dereference condition, states the DoS impact, notes that the affected code is outside the OpenSSL FIPS module boundary, and lists the remediation to update to V5.0 or later. Published and modified timing used here comes from the supplied CVE and source timeline fields (published 2026-05-12; modified 2026-05-14).

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.