CVE-2020-27632Network attack vector

TCP session hijacking via predictable sequence numbers

Published Mar 10, 2021 · Updated Aug 4, 2024

Insufficiently random TCP ISNs in Siemens SIMATIC MV400 before 7.0.6 allow remote attackers to predict and hijack TCP sessions. The TCP stack seeds its initial sequence number generator with a constant and advances it by constant increments, making future sequence numbers predictable. Network access without authentication or user interaction is sufficient, and successful exploitation permits manipulation of existing TCP connections without directly disclosing data or interrupting the device.

CVSS severity7.5
High
EPSS probability1.21%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Insufficiently random TCP ISNs in Siemens SIMATIC MV400 before 7.0.6 allow remote attackers to predict and hijack TCP sessions. The TCP stack seeds its initial sequence number generator with a constant and advances it by constant increments, making future sequence numbers predictable. Network access without authentication or user interaction is sufficient, and successful exploitation permits manipulation of existing TCP connections without directly disclosing data or interrupting the device.

The record

CVE
CVE-2020-27632
Published
Mar 10, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-330, T1565.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 10, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.5Siemens ProductCERTCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-330Use of Insufficiently Random Values
T1565.002Data Manipulation: Transmitted Data Manipulation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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