Ubuntu Security Notices USN-8110-1 USN-8110-1: Net-CIDR vulnerability Publication date 18 March 2026 Overview Net-CIDR could allow unintended access to network services. Releases 24.04 LTS 22.04 LTS 20.04 LTS 18.04 LTS 16.04 LTS 14.04 LTS Open side navigation Close side navigation Packages Details Update instructions References Packages libnet-cidr-perl - module for merging IPv4 or IPv6 CIDR address ranges Details Dave Rolsky discovered that Net-CIDR did not properly sanitize IP addresses. An attacker could possibly use this to bypass IP-based restrictions. Dave Rolsky discovered that Net-CIDR did not properly sanitize IP addresses. An attacker could possibly use this to bypass IP-based restrictions. Update instructions In general, a standard system update will make all the necessary changes. Learn more about how to get the fixes. The problem can be corrected by updating your system to the following package versions: Ubuntu Release Package Version 24.04 LTS noble libnet-cidr-perl – 0.21-2ubuntu0.2 22.04 LTS jammy libnet-cidr-perl – 0.21-1ubuntu0.2 20.04 LTS focal libnet-cidr-perl – 0.20-1ubuntu0.1~esm2 Ubuntu Pro Fix available with Ubuntu Pro . 18.04 LTS bionic libnet-cidr-perl – 0.18-1ubuntu0.1~esm2 Ubuntu Pro Fix available with Ubuntu Pro . 16.04 LTS xenial libnet-cidr-perl – 0.17-1ubuntu0.16.04.1~esm2 Ubuntu Pro Fix available with Ubuntu Pro . 14.04 LTS trusty libnet-cidr-perl – 0.17-1ubuntu0.14.04.1~esm2 Ubuntu Pro Fix available with Ubuntu Pro via Legacy Support add-on. Reduce your security exposure Ubuntu Pro provides ten-year security coverage to 25,000+ packages in Main and Universe repositories, and it is free for up to five machines. Get Ubuntu Pro References CVE-2021-4456 CVE-2021-4456