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CVE-2020-27633

26
FAUCET Score

CVE-2020-27633 describes an improper randomization of TCP Initial Sequence Numbers (ISNs) in FNET 4.6.3, affecting butok fnet products. This critical vulnerability, with a CVSS score of 9.1, allows unauthenticated attackers to remotely hijack TCP connections and spoof communications with low attack complexity, leading to high confidentiality and integrity impacts. Despite its severity, there is no evidence of active exploitation, public exploit code (Metasploit, Nuclei, ExploitDB), or significant community discussion, though it has received limited media coverage.

Impacted Technologies

VendorProductVersion(s)CPE
4.6.3CPE matchmatch criteria
cpe:2.3:a:butok:fnet:4.6.3:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

9.1CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
NONE
Exploitability Score
3.9
Impact Score
5.2
CvssVersion
3.1

Exploit Intelligence

EPSS Score
0.87%
Probability of exploitation in next 30 days
EPSS Percentile
55.1%
Percentile rank of EPSS score among Peer Group
As of 2026-07-26
Model: v2026.06.15
This CVE's current EPSS score of 0.0087 is in the 39th percentile among its peer group of 36,835 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.3 Bluesky, 0.3 Mastodon, and 2.4 GitHub mentions.

Media Mentions

The average CVE in this peer group has 0.3 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Remediation records are not available for this CVE.

References

cisa.gov / news-events/ics-advisories/icsa-21-042-01
Third Party AdvisoryUS Government Resource
forescout.com
Third Party Advisory
forescout.com / resources/numberjack-weak-isn-generation-in-embedded-tcpip-stacks
Third Party Advisory