Security readout for executives and security teams
Plain-English summary
CVE-2021-40083 is a remote-triggerable assertion failure in Knot Resolver before 5.3.2. In practical terms, a DNS resolver using affected versions could crash or fail when processing a specific DNSSEC NSEC3 wildcard proof edge case, creating an availability risk for DNS-dependent services.
Executive priority
Treat this as a targeted availability risk for DNS infrastructure. It is not documented as actively exploited, but affected resolvers can support critical connectivity, so upgrade planning should be prompt where Knot Resolver is in use.
Technical view
The issue affects Knot Resolver before 5.3.2 and involves NSEC3 records with too many iterations during a positive wildcard proof. The published description indicates an assertion failure reachable remotely. The sources do not provide CVSS, CWE, detailed impact metrics, or confirmed exploit activity.
Likely exposure
Exposure is most likely where Knot Resolver before 5.3.2 is deployed as a recursive resolver, especially if reachable by untrusted networks or used in business-critical DNS paths.
Exploitation context
The source bundle does not show CISA KEV listing or public active exploitation evidence. The described condition is remotely triggerable, but no exploit steps, indicators, or weaponized activity are provided.
Researcher notes
Evidence is limited to the CVE description and upstream merge request reference. The vulnerable condition is specific to DNSSEC NSEC3 positive wildcard proof handling. Further analysis should rely on upstream patch notes or code review, not assumptions about broader DNS products.
Mitigation direction
- Upgrade Knot Resolver deployments to 5.3.2 or later where applicable.
- Check NIC.CZ Knot Resolver guidance for any related operational recommendations.
- Prioritize internet-facing or shared recursive resolver infrastructure.
- Ensure resolver process monitoring and restart alerting are enabled.
Validation and detection
- Inventory Knot Resolver instances and record their exact versions.
- Flag any deployment running a version earlier than 5.3.2.
- Review resolver logs for assertion failures or unexpected restarts.
- Confirm upgraded resolvers continue handling DNSSEC validation normally.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CVE-2021-40083 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Unknown
- CVSS
- Not scored
- Known Exploited
- No
- Published
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS and timeline data
No CVSS vectors or timeline events were available in the normalized CVE source material.
Source materials
- CVE List V5 sourceCVE List V5
- https://gitlab.nic.cz/knot/knot-resolver/-/merge_requests/1169CVE reference · x_refsource_MISC
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.