CVE-2026-18664

Wrong interpretation of ACL ranges

Published Aug 26, 2026 CVSS 4.0 · 8.2 High EPSS < 1% KEV · Not listed
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.

Remediation

Vendor Solution

This issue is fixed in 4.15.1 and all later versions.

Tracking

Sign in to view the affected projects.

Advisories

No advisories available
History
Type Values Removed Values Added
CPEs cpe:2.3:a:nlnetlabs:nsd:*:*:*:*:*:*:*:*
Metrics cvssV3_1

{'score': 9.1, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H'}

Type Values Removed Values Added
First Time appeared Nlnetlabs
Nlnetlabs nsd
Vendors & Products Nlnetlabs
Nlnetlabs nsd
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
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.
Title Wrong interpretation of ACL ranges
Weaknesses CWE-284
CWE-697
References
Metrics cvssV4_0

{'score': 8.2, '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'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
NLnet Labs
Published
Updated
Aug 26, 2026, 2:47 PM
Reserved
Aug 3, 2026, 1:23 PM
Status
Analyzed
Published
Aug 26, 2026, 9:16 AM
Modified
Sep 8, 2026, 8:02 PM