TCP Sequence Number Validation Bypass in Siemens Interniche IP-Stack
CVE-2025-40820 is a high-severity flaw in the Siemens Interniche IP-Stack used by multiple Siemens industrial products. The issue stems from improper enforcement of TCP sequence number validation in specific scenarios, where the stack accepts sequence numbers within an overly broad range instead of strictly validating them. This weakness can allow an unauthenticated remote attacker to inject spoofed IP packets and interfere with TCP connection setup. The vulnerability affects TCP-based services and can be exploited without authentication, but successful exploitation requires the attacker to send spoofed packets at precisely timed moments during the TCP exchange. The primary consequence described in the available advisories is disruption of connection establishment leading to denial of service.
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Impact, mitigation & remediation
What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.
Impact
What an attacker gets, and what they’ve been doing with it.
Mitigation
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Remediation
Patch, then assume compromise.
Exploits
No public exploits tracked yet. Mallory keeps watching.
No public exploit code observed for this vulnerability.
Recent activity
9 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A TCP sequence number validation bypass in affected products that can enable an unauthenticated remote attacker (with the ability to inject precisely timed spoofed IP packets) to interfere with TCP connection setup, potentially causing denial of service for TCP-based services.
A vulnerability in multiple Siemens industrial products that will not be patched in many affected models. The flaw can lead to remote code execution, denial of service, or data confidentiality compromise.
The version that knows your environment.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.