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CVE-2021-40523

25
FAUCET Score

CVE-2021-40523 is a denial-of-service vulnerability affecting Contiki 3.0, specifically within its Telnet option negotiation. An attacker can exploit improper handling of exception conditions during negotiation, causing the server to fail to respond to WILL/DO commands and potentially exhaust a fixed buffer space. This vulnerability carries a high CVSS score of 7.5, indicating a network-based attack with low complexity leading to high availability impact. There is currently no evidence of active exploitation, publicly available exploit code (Metasploit, Nuclei, ExploitDB), or significant community discussion or media coverage surrounding this CVE.

Impacted Technologies

VendorProductVersion(s)CPE
3.0CPE matchmatch criteria
cpe:2.3:o:contiki-os:contiki:3.0:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

7.5HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
NONE
Integrity Impact
NONE
Availability Impact
HIGH
Exploitability Score
3.9
Impact Score
3.6
CvssVersion
3.1

Exploit Intelligence

EPSS Score
0.96%
Probability of exploitation in next 30 days
EPSS Percentile
57.9%
Percentile rank of EPSS score among Peer Group
As of 2026-07-25
Model: v2026.06.15
This CVE's current EPSS score of 0.0096 is in the 32nd percentile among its peer group of 51,485 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.1 Mastodon, and 0.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (1)

github_advisorypatch availablevia nvd_reference
View patch

References

github.com / contiki-os/contiki/issues/2686
PatchThird Party Advisory