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Fencer Intel
critical 9.1

CVE-2020-27635 json

In PicoTCP 1.7.0, TCP ISNs are improperly random.

published 3y ago modified 4mo ago also EUVD-2020-20142

cvss
9.1
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.9%
EPSS 0.9% chance of exploitation in 30 days, percentile 59%
public exploits
0
none known

Summary

In PicoTCP 1.7.0, TCP ISNs are improperly random.

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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 SSVC

Exploitation
none
Automatable
yes
Technical impact
total
Assessed
2y ago

Exploit prediction

0.87% chance of exploitation in the next 30 days, higher than 59% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
NVD 3.1 9.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Classification

Weakness
  • CWE-330 Use of Insufficiently Random Values

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.