What’s Vulnerable › Vulnerabilities

CVE-2020-27632

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 2.1% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-03-10 · updated 2026-06-17

Description

In SIMATIC MV400 family versions prior to v7.0.6, the ISN generator is initialized with a constant value and has constant increments. An attacker could predict and hijack TCP sessions.

Affected products

• Siemens Simatic Mv420 Firmware: before 7.0.6 — fixed in 7.0.6
• Siemens Simatic Mv440 Firmware: before 7.0.6 — fixed in 7.0.6

How to fix

Upgrade to a fixed version: Siemens Simatic Mv420 Firmware 7.0.6; Siemens Simatic Mv440 Firmware 7.0.6. Check the vendor advisory for mitigations.

References

• https://cert-portal.siemens.com/productcert/pdf/ssa-599268.pdf
• https://www.cisa.gov/news-events/ics-advisories/icsa-21-042-01
• https://www.forescout.com/resources/numberjack-weak-isn-generation-in-embedded-tcpip-stacks/
• https://cert-portal.siemens.com/productcert/pdf/ssa-599268.pdf
• https://www.cisa.gov/news-events/ics-advisories/icsa-21-042-01
• https://www.forescout.com/resources/numberjack-weak-isn-generation-in-embedded-tcpip-stacks/

Get alerted when CVE-2020-27632 or the next vulnerability affects your stack