JFrog Security Research

XRAY-194054 - NicheStack TCP ISNs are generated in a predictable manner

CVE-2020-35685 | CVSS 9.1

JFrog Severity:high

Published 4 Aug. 2021 | Last updated 4 Aug. 2021

NicheStack TCP ISNs are generated in a predictable manner

InterNiche TCP/IP stack

InterNiche (, 4.3), fixed in 4.3

An issue was discovered in HCC Nichestack 3.0. The code that generates Initial Sequence Numbers (ISNs) for TCP connections derives the ISN from an insufficiently random source. As a result, an attacker may be able to determine the ISN of current and future TCP connections and either hijack existing ones or spoof future ones. (Proper ISN generation should aim to follow at least the specifications outlined in RFC 6528.)

No PoC is supplied for this issue

No vulnerability mitigations are supplied for this issue

(JFrog) INFRA:HALT New Vulnerabilities Impacting OT and Critical Infrastructure

NVD