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Fencer Intel
high 7.5

CVE-2020-27632 json

In SIMATIC MV400 family versions prior to v7.0.6, the ISN generator is initialized with a constant value and has constant increments.

published 5y ago modified 4mo ago also EUVD-2020-20139

cvss
7.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
2.1%
EPSS 2.1% chance of exploitation in 30 days, percentile 82%
public exploits
0
none known

Summary

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.

Patch / fix

  • siemens simatic_mv420_firmware 7.0.6
  • siemens simatic_mv440_firmware 7.0.6

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

cisa ICSA-21-042-01 updated cvss 7.5

Multiple Embedded TCP/IP Stacks (Update B)

  • multiple Capital VSTAR multiple CycloneTCP <= 1.9.6 multiple FNET 4.6.3 multiple MPLAB Net <= 3.6.1 multiple NDKTCPIP <= 2.25 multiple Nucleus NET All < 5.2
    +9 more products
    multiple Nucleus ReadyStart for ARM MIPS and PPC < 2012.12 multiple Nucleus Source Code multiple Nut/Net <= 5.1 multiple picoTCP (EOL) <= 1.7.0 multiple picoTCP-NG <= 1.7.0 multiple uC/TCP-IP (EOL) <= 3.6.0 multiple uIP (EOL) <= 1.0 multiple uIP-Contiki-NG <= 4.5 multiple uIP-Contiki-OS (end-of-life [EOL]) <= 3.0
    affected: vendor fix, mitigation “uIP-Contiki-OS (end-of-life [EOL]). See general recommendations below.” github.com

From CISA ICS and IT advisories (CSAF, https://github.com/cisagov/CSAF), a U.S. Government work; changed: reduced to products, statuses and remediations. CISA notification · csaf

cisa ICSA-21-068-07 updated cvss 7.5

Siemens TCP Stack of SIMATIC MV400

  • Siemens SIMATIC MV400 family <V7.0.6
    affected: fixed in V7.0.6

Facts from CISA's republication of the vendor's own advisory (CSAF); the linked advisory is the authoritative source. CISA notification · csaf

Exploit prediction

2.14% chance of exploitation in the next 30 days, higher than 82% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
NVD 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
NVD 2.0 5.0 AV:N/AC:L/Au:N/C:N/I:P/A:N

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.