Vulnerability · Published Aug 26, 2026 · Assigned by NLnet Labs
CVE-2026-18664Wrong interpretation of ACL ranges
High 8.2
In plain English
A high-severity improper access control in NSD from NLnet Labs. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 38% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | nsd | no fix listed | DEBIAN-CVE-2026-18664 |
| Debian:13 | nsd | no fix listed | DEBIAN-CVE-2026-18664 |
| Debian:14 | nsd | 4.15.1-1 | DEBIAN-CVE-2026-18664 |
| Ubuntu:26.10 | nsd | no fix listed | UBUNTU-CVE-2026-18664 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| NLnet Labs | NSD | 3.0.0 – before 4.15.1 |
Weakness: CWE-284, CWE-697 · 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
References
- https://www.nlnetlabs.nl/downloads/nsd/CVE-2026-18664.txt vendor-advisory