How severe is CVE-2021-38311?

CVE-2021-38311 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2021-38311 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (57th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-38311?

CVE-2021-38311 affects Contiki-os Contiki. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-38311?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-38311 published?

CVE-2021-38311 was published on 2021-08-09 and last updated on 2026-06-17.

CVE-2021-38311

CVE-2021-38311 is a high-severity vulnerability in Contiki-os Contiki with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-835.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 4.3
EPSS exploit prediction: 1% (57th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-835
Affected product: Contiki-os Contiki
Published: 2021-08-09
Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is 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.
How severe is CVE-2021-38311?: CVE-2021-38311 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2021-38311 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (57th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-38311?: CVE-2021-38311 affects Contiki-os Contiki. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-38311?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-38311 published?: CVE-2021-38311 was published on 2021-08-09 and last updated on 2026-06-17.

References

https://github.com/contiki-os/contiki/issues/2685

Affected products (1)

cpe:2.3:o:contiki-os:contiki:3.0:*:*:*:*:*:*:*

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