Net::CIDR::Lite Flaws Enable IP-Based Access Control Bypass
Three vulnerabilities in the Net::CIDR::Lite Perl library allow attackers to bypass IP address-based access controls through malformed IP address handling. Ubuntu has released security updates addressing octal prefix parsing, IPv6 validation, and IPv4-mapped IPv6 address mishandling.
TL;DR
- Net::CIDR::Lite contains three CVEs enabling IP access control bypass via malformed addresses
- Leading zero characters in IPv4 addresses can evade filters (CVE-2021-47154, Ubuntu 16.04/18.04 LTS)
- Improper IPv6 group validation allows attackers to craft addresses that pass security checks (CVE-2026-40198)
- IPv4-mapped IPv6 address mishandling creates additional bypass vectors (CVE-2026-40199)
- Organizations using this library for IP-based access control should apply updates immediately
The Net::CIDR::Lite Perl library, commonly used for IP address range validation and access control enforcement, contains three distinct vulnerabilities that could allow remote attackers to circumvent IP-based security policies. These flaws stem from improper handling of edge cases in IP address parsing and validation logic.
The vulnerabilities affect different IP address formats and validation routines. Organizations relying on this library for firewall rules, API access controls, or other IP-based security mechanisms should treat these issues as high-priority, as successful exploitation directly undermines access control decisions.
Vulnerability Details
- CVE-2021-47154: Extraneous leading zeros in IPv4 addresses bypass filters (Ubuntu 16.04 LTS and 18.04 LTS only)
- CVE-2026-40198: Improper IPv6 group count validation in uncompressed addresses allows crafted payloads to pass security checks
- CVE-2026-40199: Mishandling of IPv4-mapped IPv6 addresses creates additional bypass vectors for IP-based access controls
Security Impact & Recommendations
- Access control systems relying on Net::CIDR::Lite for IP validation may be circumvented by attackers using specially crafted addresses
- Applications using this library for rate limiting, geo-blocking, or firewall rule enforcement are at direct risk
- Affected Ubuntu versions (16.04 LTS, 18.04 LTS) should apply USN-8406-1 patches immediately
- Organizations should audit their use of Net::CIDR::Lite and validate that IP-based security policies are functioning as intended
- Consider implementing additional validation layers or upgrading to patched versions of the library
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