CVE-2026-18664Network attack vector

IP range ACL bypass via endian-mismatched comparisons

Published Aug 26, 2026 · Updated Aug 26, 2026

Improper access control in NLnet Labs NSD 3.0.0 through 4.15.0 allows remote attackers to bypass IP range ACLs. The ACL evaluator compares network-byte-order IPv4 values directly as host-endian 32-bit integers and evaluates IPv6 values as four host-endian integers. Exploitation requires a little-endian host and a hyphenated address range; matching unintended addresses can obtain access that the configured range was intended to deny.

CVSS severity8.2
High
EPSS probability0.33%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper access control in NLnet Labs NSD 3.0.0 through 4.15.0 allows remote attackers to bypass IP range ACLs. The ACL evaluator compares network-byte-order IPv4 values directly as host-endian 32-bit integers and evaluates IPv6 values as four host-endian integers. Exploitation requires a little-endian host and a hyphenated address range; matching unintended addresses can obtain access that the configured range was intended to deny.

The record

CVE
CVE-2026-18664
Published
Aug 26, 2026
Updated
Aug 26, 2026
Vendor
NLnet Labs
Product
NSD
Classifications
CWE-697, CWE-284, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 26, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 26, 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=3.0.0 <4.15.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

NLnet Labs · NSDversion=3.0.0 <4.15.1

Published CVSS scores

8.2NLnet LabsCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

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-697Incorrect Comparison
CWE-284Improper Access Control
T1190Exploit Public-Facing Application

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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