High severity · published Dec 9, 2025
CVE-2025-40820
Affected products do not properly enforce TCP sequence number validation in specific scenarios but accept values within a broad range
7.5
CVSS
0.5%
EPSS
No
On KEV
Description
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.5% · higher than 42% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
SA
SIDOOR ATD430W · Siemens
0 · source: vendor
SC
SIMATIC CFU DIQ · Siemens
before V2.0.0 · source: vendor
SC
SIMATIC CFU PA · Siemens
before V2.0.0; before V2.0.0 · source: vendor