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CVE-2026-18664

9.1, critical

NLnet Labs NSD Improper Access Control Vulnerability

NVD (opens in a new tab) CVE.org (opens in a new tab)
CVSS
9.1, critical critical CVSS v3.1
EPSS, next 30 days
0.3% higher than 16.4% of scored CVEs
Exploitation
No public evidence
Published
26 Aug 2026a month ago

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.

Details

Vendor
NLnet Labs
Product
NSD
Weakness
CWE-284 (opens in a new tab)
Status
Analyzed
Updated
8 Sept 2026
Assigner
sep@nlnetlabs.nl

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

References 1

Advisories 1

The kind is read from NVD's tags where present and from the shape of the URL otherwise, so treat it as a hint.

Other NLnet Labs CVEs

Every NLnet Labs CVE we hold

Same vendor in what we hold, not a known link between the flaws.

  • CVE-2026-81642 NLnet Labs Unbound Heap-based Buffer Overflow Vulnerability EPSS 1% 9.8, critical
  • CVE-2026-82717 NLnet Labs Unbound Heap-based Buffer Overflow Vulnerability EPSS 0.8% 9.8, critical
  • CVE-2026-80225 NLnet Labs Unbound Allocation of Resources Without Limits or Throttling Vulnerability EPSS 0.5% 7.5, high
  • CVE-2026-85501 NLnet Labs Unbound Allocation of Resources Without Limits or Throttling Vulnerability EPSS 0.5% 7.5, high
  • CVE-2026-18916 NLnet Labs NSD Integer Underflow Vulnerability EPSS 0.3% 7.5, high
  • CVE-2026-19401 NLnet Labs NSD Uncontrolled Resource Consumption Vulnerability EPSS 0.3% 7.5, high
  • CVE-2026-19538 The BLOCKED access control list items that are evaluated to deny access on the the proxy protocol port can be bypassed completely when… EPSS 0.2% 7.5, high

Beyond this page

Is CVE-2026-18664 in your network?

This page tells you how dangerous CVE-2026-18664 is out there. Whether it sits on one of your devices, only a scan of your own network can tell. That is what our systems do, every day, for the companies we protect.

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Check your exposure

Assembled from the NVD 2.0 API, the CISA Known Exploited Vulnerabilities Catalog and FIRST EPSS. Scores are as of our last collection on 17 Oct 2026, not the live upstream state.