CVE-2020-27213
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.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.97%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
Description
An issue was discovered in Ethernut Nut/OS 5.1. 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. While the ISN generator seems to adhere to RFC 793 (where a global 32-bit counter is incremented roughly every 4 microseconds), proper ISN generation should aim to follow at least the specifications outlined in RFC 6528.
- CVSS 3.1
- 7.5 HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
- EPSS
- 0.97% probability · 60th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-330
- Affected
- ethernut/nut\/os
- Source
- cve@mitre.org
References
- http://lists.egnite.de/mailman/listinfo/en-nut-announceNot Applicable
- http://www.ethernut.de/en/download/index.htmlRelease Notes
- https://www.cisa.gov/news-events/ics-advisories/icsa-21-042-01Third Party Advisory, US Government Resource
- https://www.forescout.com/resources/numberjack-weak-isn-generation-in-embedded-tcpip-stacks/Exploit, Third Party Advisory
- http://lists.egnite.de/mailman/listinfo/en-nut-announceNot Applicable
- http://www.ethernut.de/en/download/index.htmlRelease Notes
- https://www.cisa.gov/news-events/ics-advisories/icsa-21-042-01Third Party Advisory, US Government Resource
- https://www.forescout.com/resources/numberjack-weak-isn-generation-in-embedded-tcpip-stacks/Exploit, Third Party Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.