CVE-2023-26249Network attack vector

DNS service interruption via unpenalized TCP reconnects

Published Feb 21, 2023 · Updated Mar 14, 2025

Resource exhaustion in Knot Resolver before 5.6.0 allows remote attackers to interrupt DNS service through crafted client queries. The outbound TCP close path ended a session without marking its server address as failed when no DNS message had been produced, so selection retried it up to about 100 times. Exploitation requires a client query that reaches a DNS server which closes the connection unanswered; the resulting connection churn consumes resolver and server resources.

CVSS severity7.5
High
EPSS probability0.71%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Resource exhaustion in Knot Resolver before 5.6.0 allows remote attackers to interrupt DNS service through crafted client queries. The outbound TCP close path ended a session without marking its server address as failed when no DNS message had been produced, so selection retried it up to about 100 times. Exploitation requires a client query that reaches a DNS server which closes the connection unanswered; the resulting connection churn consumes resolver and server resources.

The record

CVE
CVE-2023-26249
Published
Feb 21, 2023
Updated
Mar 14, 2025
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-770, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 21, 2023CVE publishedPublication date reported by the CVE source.
  2. Mar 14, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.5CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-770Allocation of Resources Without Limits or Throttling
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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