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CVE-2021-40083

24
FAUCET Score

CVE-2021-40083 is an assertion failure vulnerability affecting Knot Resolver versions prior to 5.3.2. This flaw can be triggered remotely by an attacker using a specific NSEC3 configuration involving excessive iterations for a positive wildcard proof. With a CVSS score of 7.5 (High), this vulnerability allows for a denial of service (availability impact) with low attack complexity and no user interaction required. There is currently no evidence of active exploitation, public exploit code (Metasploit, Nuclei, ExploitDB), or significant community discussion or media coverage surrounding this CVE.

Impacted Technologies

VendorProductVersion(s)CPE
< 5.3.2CPE matchmatch criteria
cpe:2.3:a:nic:knot_resolver:*:*:*:*:*:*:*:*

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
1.42%
Probability of exploitation in next 30 days
EPSS Percentile
70.1%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0142 is in the 51st percentile among its peer group of 51,551 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

Remediation records are not available for this CVE.

References

gitlab.nic.cz / knot/knot-resolver/-/merge_requests/1169
PatchThird Party Advisory