CVE-2026-49942: Net::CIDR::Set Network Mask Validation Bypass (CVSS 7.3)

Technical summary

The vulnerability resides in Net::CIDR::Set's network mask parsing logic. When validating CIDR notation (e.g., 192.168.1.0/24), the library fails to strictly validate the mask portion. The parser accepts Unicode digit characters—including Arabic-Indic digits (U+0661 and similar)—which are silently ignored or misinterpreted. Non-digit characters in the mask field are also not rejected. Furthermore, leading zeros in the numeric portion are interpreted as decimal (base-10) rather than octal (base-8), deviating from expected network configuration semantics. This combination allows an attacker to craft CIDR specifications that pass validation but represent broader or unintended network ranges, effectively expanding the scope of permitted or denied traffic beyond what administrators configured.

Business impact

Organizations using Net::CIDR::Set for network access control decisions—such as IP allow/blocklists, firewall rule generators, or API gateway configurations—face the risk of security policy bypass. An attacker could craft specially formatted CIDR blocks that are accepted by the library but represent unintended network ranges, potentially granting access to systems or resources that should be restricted. The impact varies by deployment: libraries relying on Net::CIDR::Set for authorization logic could fail to correctly enforce network-based access restrictions, leading to confidentiality, integrity, and availability risks.

Affected systems

Net::CIDR::Set through version 0.20 is affected. Any Perl application or module that depends on Net::CIDR::Set for network validation, firewall configuration, access control, or CIDR block manipulation is at risk. This includes custom applications, configuration management tools, and infrastructure automation scripts that use this library to enforce network policies.

Exploitability

Exploitation requires no authentication and no user interaction. An attacker only needs to supply specially crafted CIDR notation—using Unicode digits or leading zeros—to a system or application that accepts network specifications and processes them through Net::CIDR::Set. The attack surface depends on how exposed the network configuration interface is; if an application accepts user-supplied CIDR blocks or allows remote configuration, the risk is elevated. The CVSS score of 7.3 (HIGH) reflects the network-accessible, low-complexity nature of exploitation and the combined impact on confidentiality, integrity, and availability.

Remediation

Upgrade Net::CIDR::Set to a patched version that implements strict validation of network masks. Verify against the vendor advisory for the specific version number that resolves this issue. Until patching is possible, audit all CIDR specifications in use and manually verify they conform to standard dotted-decimal notation (e.g., 192.168.1.0/24 with only ASCII digits and appropriate octal/decimal handling). Consider restricting the input sources for network specifications to trusted administrators only.

Patch guidance

Contact the Net::CIDR::Set maintainers or check the official Perl CPAN repository for a patched release. Verify against the vendor advisory for the minimum version that includes the mask validation fix. Once a patch is available, test it in a non-production environment to ensure existing CIDR configurations are correctly re-interpreted under the stricter validation rules. Update all dependent applications and modules systematically to avoid configuration drift.

Detection guidance

Monitor applications and configuration systems that use Net::CIDR::Set for unusual CIDR specifications, particularly those containing non-ASCII characters or unexpected leading zeros. Review logs of network policy updates or access control modifications for entries that may have been injected using Unicode or malformed masks. Audit current CIDR block configurations to identify any that use non-standard notation; these may indicate attempted or successful exploitation. If source code is available, scan for calls to Net::CIDR::Set functions with untrusted input.

Why prioritize this

This vulnerability merits rapid prioritization because it directly undermines network access control mechanisms that organizations rely on for security. The ability to bypass firewall rules, IP blocklists, or access policies through crafted input is a high-impact security flaw. The low complexity of exploitation and lack of authentication requirements increase urgency. Organizations should prioritize patching and validating their configurations within one to two weeks, especially those using Net::CIDR::Set for critical access control decisions.

Risk score, explained

The CVSS 7.3 (HIGH) score reflects: (1) Network-accessible attack vector with no authentication or user interaction required; (2) Low attack complexity—an attacker simply supplies malformed CIDR notation; (3) Impact across confidentiality (access to restricted resources), integrity (unintended network policy modifications), and availability (potential denial or disruption). The vulnerability is not rated critical because it requires the affected library to be in the data path of a security decision, and impact depends on how strictly the host application relies on the library's output.

Frequently asked questions