CVE-2021-38311Network attack vector

Remote service interruption via Telnet acknowledgment loop

Published Aug 9, 2021 · Updated Aug 4, 2024

Infinite-loop handling in Contiki 3.0 Telnet allows remote attackers to interrupt service by sending DONT or WONT requests. The option-negotiation handler incorrectly acknowledges disabled options with WONT or DONT, permitting two peers to exchange acknowledgments indefinitely. A reachable Telnet service is required, and the resulting loop consumes excessive CPU without reported confidentiality or integrity impact.

CVSS severity7.5
High
EPSS probability0.94%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Infinite-loop handling in Contiki 3.0 Telnet allows remote attackers to interrupt service by sending DONT or WONT requests. The option-negotiation handler incorrectly acknowledges disabled options with WONT or DONT, permitting two peers to exchange acknowledgments indefinitely. A reachable Telnet service is required, and the resulting loop consumes excessive CPU without reported confidentiality or integrity impact.

The record

CVE
CVE-2021-38311
Published
Aug 9, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-835, T1499.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 9, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

4.3NIST National Vulnerability DatabaseAV:N/AC:M/Au:N/C:N/I:N/A:P
7.5NIST National Vulnerability DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-835Loop with Unreachable Exit Condition ('Infinite Loop')
T1499.002Service Exhaustion

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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