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Vulnerabilities

Vulnerability · CVE-2025-40820

Affected products do not properly enforce TCP sequence number validation in specific scenarios but accept values within a broad range.

Published Dec 9, 2025 · catalog updated Dec 9, 2025 · Siemens SIMATIC S7-200 SMART CPU SR20

Last checked Nov 2, 2026. A connected source was read within the last 7 days.

Check if you run it

No confirmed exploitation is on record for CVE-2025-40820. EPSS is 0.49%. Act only if a listed version of Siemens SIMATIC S7-200 SMART CPU SR20 is installed.

Gaps on this record

  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
High8.7
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.49%
Remediation
Version ranges on file
Affected products
vendor Siemens SIMATIC S7-200 SMART CPU SR20 0 <*

Affected products do not properly enforce TCP sequence number validation in specific scenarios but accept values within a broad range. This could allow an unauthenticated remote attacker e.g. to interfere with connection setup, potentially leading to a denial of service. The attack succeeds only if an attacker can inject IP packets with spoofed addresses at precisely timed moments, and it affects only TCP-based services.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • vendor Siemens SIMATIC S7-200 SMART CPU SR20 0 <*0 <*

How to fix CVE-2025-40820

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2025-40820. EPSS is 0.49%. Act only if a listed version of Siemens SIMATIC S7-200 SMART CPU SR20 is installed.

Which versions are affected?

Compare what you have installed with Siemens SIMATIC S7-200 SMART CPU SR20 0 <* 0 <*. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

No weakness class is stored. EPSS 0.49%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

  1. Dec 9, 2025 · EUVD

    Detected

    Affected products do not properly enforce TCP sequence number validation in specific scenarios but accept values within a broad range. This could allow an unauthenticated remote attacker e.g. to interfere with connection setup, potentially leading to a denial of service. The attack succeeds only if an attacker can inject IP packets with spoofed addresses at precisely timed moments, and it affects

  2. Dec 9, 2025 · EUVD

    Updated

    Affected products do not properly enforce TCP sequence number validation in specific scenarios but accept values within a broad range. This could allow an unauthenticated remote attacker e.g. to interfere with connection setup, potentially leading to a denial of service. The attack succeeds only if an attacker can inject IP packets with spoofed addresses at precisely timed moments, and it affects

Sources

  • CVE.orgVulnerability recordCVE-2025-40820

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2025-40820

    30-day exploitation probability 0.49%

    first.org
  • EUVDVulnerability recordEUVD-2025-201923

    Affected products do not properly enforce TCP sequence number validation in specific scenarios but accept values within a broad range. This could allow an unauthenticated remote attacker e.g. to interfere with connection setup, potentially leading to a denial of service. The atta

    euvd.enisa.europa.eu

References

Freshness

Last verified in this catalog Nov 2, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.

  • FIRST EPSSNov 2, 2026
  • CVE.orgOct 27, 2026
  • EUVDOct 27, 2026