What is CVE-2021-38311?

CVE-2021-38311 is a high-severity vulnerability in Contiki-Os Contiki, classified under Loop with Unreachable Exit Condition (Infinite Loop). CVSS score: 7.5/10. Published 2021-08-09.

How severe is CVE-2021-38311?

High severity. CVSS v3 base score is 7.5 out of 10.

Vulnerability in Contiki-Os Contiki

CVE-2021-38311

In Contiki 3.0, potential nonterminating acknowledgment loops exist in the Telnet service. When the negotiated options are already disabled, servers still respond to DONT and WONT requests with WONT or DONT commands, which may lead to infinite acknowledgment loops, denial of service, and excessive CPU consumption.

Published 2021-08-09 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.009 (60.9th percentile), scored 2026-10-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 61st percentile — 60.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.009 · newest: 0.009 · change: 0.000

Affected products

Contiki-Os Contiki — versions 3.0

Weakness classification (CWE)

CWE-835 — Loop with Unreachable Exit Condition (Infinite Loop)

References

github.com/contiki-os/contiki/issues/2685 (Exploit, Patch, Third Party Advisory, Issue Tracking)

Frequently asked questions

What is CVE-2021-38311?: CVE-2021-38311 is a high-severity vulnerability in Contiki-Os Contiki, classified under Loop with Unreachable Exit Condition (Infinite Loop). CVSS score: 7.5/10. Published 2021-08-09.
How severe is CVE-2021-38311?: High severity. CVSS v3 base score is 7.5 out of 10.