CVE-2026-50251Network attack vector

DNS resolution disruption via repeated cache flushes

Published Jul 22, 2026 · Updated Jul 22, 2026

Denial of service in NLnet Labs Unbound 1.25.1 and earlier allows remote attackers to repeatedly clear DNS caches via crafted glue. The iterator follows in-bailiwick 0.0.0.0 or ::0 glue, then counts Unbound's loopback answer as unwanted because its source differs from the glue address. Exploitation requires unwanted-reply-threshold above zero, control of a DNS delegation, and an OS that routes the zero address; repeated threshold hits interrupt resolution by flushing message and rrset caches.

CVSS severity5.3
Medium
EPSS probability0.25%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in NLnet Labs Unbound 1.25.1 and earlier allows remote attackers to repeatedly clear DNS caches via crafted glue. The iterator follows in-bailiwick 0.0.0.0 or ::0 glue, then counts Unbound's loopback answer as unwanted because its source differs from the glue address. Exploitation requires unwanted-reply-threshold above zero, control of a DNS delegation, and an OS that routes the zero address; repeated threshold hits interrupt resolution by flushing message and rrset caches.

The record

CVE
CVE-2026-50251
Published
Jul 22, 2026
Updated
Jul 22, 2026
Vendor
NLnet Labs
Product
Unbound
Classifications
CWE-184, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 22, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 22, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <1.25.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

NLnet Labs · Unboundversion=0 <1.25.2

Published CVSS scores

5.3NLnet LabsCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

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-184Incomplete List of Disallowed Inputs
T1499.004Endpoint Denial of Service: Application or System Exploitation

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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