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No exploitation reportedFix available

CVE-2026-18664

No exploitation reported by the sources we read.

  • Published2026-08-26
  • Fixed in4.15.1
  • WeaknessCWE-284 · CWE-697

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

When ranges are used for access control (i.e. of the form 1.2.3.4-1.2.3.25), because NSD wrongly compares the IP address with the range on little endian systems, IPs that were meant to be allowed may be denied, and, IPs that were meant to be denied access could be allowed. An IPv4 address is compared with IPv4 ranges as unsigned 32 bit numbers directly with the endianness of the host, but the values to compare are in network byte order (big-endian). With IPv6 addresses the comparison is done in 4 times a unsigned 32 bit number comparison, again with the endianness of the host where all values are actually in network bye order.

Timeline

dates in UTC
  1. 2026-08-2609:16CVE publishedNVD

Versions per branch

NVD
Nlnetlabs nsd
BranchAffectedFixed in
4.15≥ 3.0.0, < 4.15.14.15.1

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Products declared by the CNA1 product

As NLnet Labs, the CNA that assigned this CVE, declared them in the CVE record; versions as written.

  • NLnet Labs NSDother versions: not affected
    Affected
    • ≥ 3.0.0, < 4.15.1fixed in 4.15.1semver

Source: the CNA record (CVE Program), © The MITRE Corporation,CVE Terms of UseCVE recordupdated 2026-08-26

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • nsdUbuntu:Pro:26.04:LTSall versions · no fixed version listed
  • nsdUbuntu:Pro:24.04:LTSall versions · no fixed version listed
  • nsdUbuntu:Pro:22.04:LTSall versions · no fixed version listed
  • nsdUbuntu:Pro:20.04:LTSall versions · no fixed version listed
  • nsdUbuntu:Pro:18.04:LTSall versions · no fixed version listed
  • nsdUbuntu:Pro:16.04:LTSall versions · no fixed version listed
  • nsdUbuntu:26.10all versions · no fixed version listed
  • nsdDebian:14all versions · fixed in 4.15.1-1

2 more package ranges on OSV.dev

Vendor advisories

  • CVE-2026-18664 Red Hat Product Security

    nsd: NSD: Access control bypass due to incorrect IP range comparison

Full record on NVD

Fix

  1. Update Nlnetlabs nsd to 4.15.1

Advisories and patches

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof of concept
Metasploit modules
none listed
Metasploit Framework

Sources

  • CISA-ADPSSVC decisionnone2026-08-26
  • CNACVSS 4.08.2known since 2026-10-23
  • NVDCVSS 3.19.1read 2026-10-23
  • CNAweakness (CWE)CWE-284, CWE-697known since 2026-10-23
  • FIRST EPSSEPSS score0.4 %2026-11-08
  • OSVaffected packages—
  • GitHub Advisoriesadvisory—

Identifiers

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
CVSS 4.0 vector
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Published
2026-08-26
Last Modified
2026-09-08
NVD status
Analyzed
GitHub Advisory
GHSA-fw9f-54cp-j7fc

Frequently asked questions

What is CVE-2026-18664?

When ranges are used for access control (i.e. of the form 1.2.3.4-1.2.3.25), because NSD wrongly compares the IP address with the range on little endian systems, IPs that were meant to be allowed may be denied, and, IPs that were meant to be denied access could be allowed. An IPv4 address is compared with IPv4 ranges as unsigned 32 bit numbers directly with the endianness of the host, but the values to compare are in network byte order (big-endian). With IPv6 addresses the comparison is done in 4 times a unsigned 32 bit number comparison, again with the endianness of the host where all values are actually in network bye order.

Is CVE-2026-18664 actively exploited?

Active exploitation of CVE-2026-18664 has not been confirmed. Its EPSS score was 0.4% on 2026-11-08, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2026-18664?

CVE-2026-18664 has a CVSS v3 base score of 9.1 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H.

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