CVE-2026-56416Network attack vector

Resolver service interruption via truncated multi-domain RDATA

Published Jul 22, 2026 · Updated Jul 22, 2026

Heap buffer overflow in NLnet Labs Unbound 1.25.1 and earlier allows remote attackers to interrupt resolver service via malformed DNSSEC data. The validator passes an unchecked pointer for a missing second domain name to query_dname_tolower(), which scans stale scratch-buffer bytes past the heap allocation. Exploitation requires control of a DNSSEC-signed authoritative server and a reduced non-default msg-buffer-size; the bounded reported consequence is service interruption.

CVSS severity4.8
Medium
EPSS probability0.12%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap buffer overflow in NLnet Labs Unbound 1.25.1 and earlier allows remote attackers to interrupt resolver service via malformed DNSSEC data. The validator passes an unchecked pointer for a missing second domain name to query_dname_tolower(), which scans stale scratch-buffer bytes past the heap allocation. Exploitation requires control of a DNSSEC-signed authoritative server and a reduced non-default msg-buffer-size; the bounded reported consequence is service interruption.

The record

CVE
CVE-2026-56416
Published
Jul 22, 2026
Updated
Jul 22, 2026
Vendor
NLnet Labs
Product
Unbound
Classifications
CWE-354, 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

4.8NLnet LabsCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/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.

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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-354Improper Validation of Integrity Check Value
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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