Knot DNS up to 3.4.9/3.5.3 mod-onlinesign input validation

CVSS Meta Temp Score
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Current Exploit Price (≈)
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CTI Interest Score
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6.2$0-$5k2.82+

Summaryinfo

A vulnerability classified as critical has been found in Knot DNS up to 3.4.9/3.5.3. Affected by this issue is some unknown functionality of the component mod-onlinesign. This manipulation causes input validation. This vulnerability is handled as CVE-2026-39155. The attack can be initiated remotely. There is not any exploit available.

Detailsinfo

A vulnerability has been found in Knot DNS up to 3.4.9/3.5.3 and classified as critical. Affected by this vulnerability is some unknown processing of the component mod-onlinesign. The manipulation with an unknown input leads to a input validation vulnerability. The CWE definition for the vulnerability is CWE-20. The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. As an impact it is known to affect integrity, and availability. The summary by CVE is:

Knot DNS before 3.4.10 and 3.5.x before 3.5.4 contains a vulnerability in mod-onlinesign where the next NSEC owner name can be computed incorrectly. This can create an overly broad authenticated denial interval, allowing downstream validating resolvers using aggressive negative caching to synthesize negative answers for legitimate names and causing resolver-side denial of service.

The advisory is shared at knot-dns.cz. This vulnerability is known as CVE-2026-39155 since 04/06/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Neither technical details nor an exploit are publicly available.

Upgrading to version 3.4.10 or 3.5.4 eliminates this vulnerability.

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Vendor

Name

Version

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 6.5
VulDB Meta Temp Score: 6.2

VulDB Base Score: 6.5
VulDB Temp Score: 6.2
VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv2info

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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Input validation
CWE: CWE-20
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined
Price Prediction: 🔍
Current Price Estimation: 🔒

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Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: DNS 3.4.10/3.5.4

Timelineinfo

04/06/2026 CVE reserved
07/23/2026 +108 days Advisory disclosed
07/23/2026 +0 days VulDB entry created
07/23/2026 +0 days VulDB entry last update

Sourcesinfo

Advisory: knot-dns.cz
Status: Confirmed

CVE: CVE-2026-39155 (🔒)
GCVE (CVE): GCVE-0-2026-39155
GCVE (VulDB): GCVE-100-382801

Entryinfo

Created: 07/23/2026 22:30
Changes: 07/23/2026 22:30 (54)
Complete: 🔍
Cache ID: 216::103

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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