Vulnerability 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 Score
CRITICAL
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Nlnetlabs | Nsd | >= 3.0.0, < 4.15.1 |
Related Weaknesses (CWE)
References
- https://www.nlnetlabs.nl/downloads/nsd/CVE-2026-18664.txtVendor Advisory
FAQ
What is CVE-2026-18664?
CVE-2026-18664 is a vulnerability with a CVSS score of 9.1 (CRITICAL). 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 ...
How severe is CVE-2026-18664?
CVE-2026-18664 has been rated CRITICAL with a CVSS base score of 9.1/10. This is considered a critical vulnerability requiring immediate attention.
Is there a patch for CVE-2026-18664?
Check the references section above for vendor advisories and patch information. Affected products include: Nlnetlabs Nsd.