CVE-2025-40820 — Affected products do not properly enforce TCP sequence number validation in specific…

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

1. Identify exposed assets running the affected vendor/product/version combinations (Siemens SIDOOR ATD430W, Siemens SIDOOR ATE530G COATED, Siemens SIDOOR ATE530S COATED…).
2. The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
3. No fix documented in the sources: reduce exposure and monitor the vendor advisory.
4. Search available logs for exploit probes, errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-940

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 15, 2026 · 3 reading(s) · max 0.49%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

• Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).

Timeline

What happened to this CVE, newest first.

• 2026
• Affected products added · siemens/sidoor atd430w, siemens/sidoor ate530g coated, siemens/sidoor ate530s coated, siemens/simatic cfu diq, siemens/s
  Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
• SSVC assessment updated
  Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
• Record published
  Oct 13, 2026
• CVSS changed · 7.5
  Oct 13, 2026 · NIST National Vulnerability Database
• Source status changed · → Deferred
  Oct 13, 2026 · NIST National Vulnerability Database
• Record created in this database
  Oct 13, 2026 · NIST National Vulnerability Database
• 2025
• CVE published
  Dec 9, 2025 · siemens

Source activity

Repeated readings are counted rather than listed.

• 1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

1 on the record

• cert-portal.siemens.com/productcert/html/ssa-915282.html
  NIST National Vulnerability Database

Elsewhere on this site

Related CVEs (same products)

• Medium CVE-2026-63356 Affected devices do not properly sanitize calculated signal names contained in imported CSV trace... 2d
• Medium CVE-2026-63357 Affected devices do not properly sanitize calculated signal data contained in imported calculated... 2d
• Critical CVE-2026-63353 Affected devices do not properly sanitize comment fields contained in imported trace files before... 2d
• Critical CVE-2026-63354 Affected devices do not properly validate and sanitize visual marker data contained in imported... 2d
• Medium CVE-2026-63355 Affected devices do not properly sanitize signal names contained in imported CSV trace files... 2d
• Medium CVE-2026-63351 Affected devices do not properly validate and sanitize visual properties of calculated signals... 2d

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

• No fixed version, patch or mitigation documented.
• No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
• No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
• No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2025-40820 is "Affected products do not properly enforce TCP sequence number validation in specific…", rated High. It affects SIDOOR ATD430W (Siemens); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 7.5 describes technical severity. EPSS 0.49% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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