What’s Vulnerable › Vulnerabilities

CVE-2021-40083

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-08-25 · updated 2026-06-17
• Weakness: CWE-617

Description

Knot Resolver before 5.3.2 is prone to an assertion failure, triggerable by a remote attacker in an edge case (NSEC3 with too many iterations used for a positive wildcard proof).

Affected products

• CZ.NIC knot-resolver: before 5.3.2 — fixed in 5.3.2

How to fix

Upgrade to a fixed version: CZ.NIC knot-resolver 5.3.2. Check the vendor advisory for mitigations.

References

• https://gitlab.nic.cz/knot/knot-resolver/-/merge_requests/1169
• https://gitlab.nic.cz/knot/knot-resolver/-/merge_requests/1169

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