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PatchSiren cyber security CVE debrief

CVE-2025-40022 Siemens CVE debrief

CVE-2025-40022 is a Linux kernel af_alg logic issue in which fields changed from bool to 1-bit u32 bitfields can store the wrong value when assignments greater than 1 are used. In the supplied advisory corpus, CISA’s Siemens CSAF entry tracks the issue under the SIMATIC S7-1500 CPU family and states that no fix is available at the time of the advisory updates. The published CVSS v3.1 score is 5.3 (Medium), with local access, high attack complexity, and integrity/availability impact.

Vendor
Siemens
Product
SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0)
CVSS
MEDIUM 5.3
CISA KEV
Not listed in stored evidence
Original CVE published
2025-06-10
Original CVE updated
2026-05-14
Advisory published
2025-06-10
Advisory updated
2026-05-14

Who should care

Operators and maintainers of the listed Siemens SIMATIC S7-1500 CPU family devices, especially teams responsible for the additional GNU/Linux subsystem and local administration access. OT asset owners should also care if they rely on CISA/Siemens advisories for lifecycle and hardening guidance.

Technical summary

Commit 1b34cbbf4f01 changed certain af_alg_ctx fields from bool to 1-bit u32 bitfields. The affected assignments to more and merge can carry values greater than 1, so the type change caused modulo-2 behavior instead of C-style boolean conversion, which could leave the field as 0 when 1 was intended. The fix restores bool.

Defensive priority

Medium priority: the issue is local and high-complexity, but it affects integrity and availability and the source advisory indicates no fix was available in the supplied timeline. Focus on access control and exposure reduction for affected deployments while monitoring Siemens/CISA updates.

Recommended defensive actions

  • Restrict interactive shell access to the additional GNU/Linux subsystem to trusted personnel only.
  • Only build and run applications from trusted sources.
  • Inventory the listed SIMATIC S7-1500 CPU family products and confirm whether they are deployed in your environment.
  • Apply least privilege and defense-in-depth controls around local administration and subsystem access.
  • Monitor the Siemens ProductCERT advisory SSA-082556 and CISA advisory ICSA-25-162-05 for updates or a vendor fix.

Evidence notes

The source corpus identifies CVE-2025-40022 as published on 2025-06-10 and last modified on 2026-05-14. The CISA CSAF advisory ICSA-25-162-05 references Siemens ProductCERT advisory SSA-082556, lists five affected SIMATIC/SIPLUS product names, assigns CVSS v3.1 5.3 (AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:H), and includes remediation text stating there is currently no fix available. The CVE description in the supplied source states the kernel bug, the bitfield conversion issue, and the bool-restoration fix.

Official resources

Publicly disclosed in the supplied CISA CSAF advisory on 2025-06-10 and updated through 2026-05-14. The provided enrichment marks it as not in CISA KEV.