CVE-2026-18664: CWE-284 Improper Access Control in NLnet Labs NSD
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.
CVSS v4.0
Score 8.2high
Affected software
NLnet Labs
NSD
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
NLnet Labs NSD 3.0.0 improperly compares IP addresses with access control ranges on little endian systems. The vulnerability occurs because IPv4 addresses are compared as unsigned 32-bit numbers using the host's endianness, while the values are actually in network byte order (big-endian). Similarly, IPv6 addresses are compared in four 32-bit segments with the same endianness issue. This results in incorrect access control decisions, potentially allowing unauthorized IPs or denying authorized ones.
Potential Impact
This vulnerability can lead to improper access control enforcement in NSD 3.0.0, where IP addresses that should have access may be denied, and IP addresses that should be denied may be granted access. This could result in unauthorized access to services or denial of service to legitimate users. There are no known exploits in the wild at this time.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. No official fix or temporary workaround has been documented as of the published date. Users should monitor NLnet Labs advisories for updates and consider restricting access control configurations until a fix is available.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- NLnet Labs
- Date Reserved
- 2026-08-03T13:23:02.012Z
- Cvss Version
- 4.0
- State
- PUBLISHED
Threat ID: 6a8ea959acd9273b499fef50
Added to database: 08/26/2026, 08:52:41 UTC
Last enriched: 09/09/2026, 19:37:31 UTC
Last updated: 10/08/2026, 06:48:15 UTC
Views: 59
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