Vulnerability · Published Feb 27, 2026 · Assigned by CPANSec
CVE-2021-4456Net::CIDR versions before 0.24 for Perl mishandle leading zeros in IP CIDR addresses, which may have unspecified impact
Medium 6.5
In plain English
A medium-severity security flaw in Net::CIDR from MRSAM. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 32% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
Net::CIDR versions before 0.24 for Perl mishandle leading zeros in IP CIDR addresses, which may have unspecified impact. The functions `addr2cidr` and `cidrlookup` may return leading zeros in a CIDR string, which may in turn be parsed as octal numbers by subsequent users. In some cases an attacker may be able to leverage this to bypass access controls based on IP addresses. The documentation advises validating untrusted CIDR strings with the `cidrvalidate` function. However, this mitigation is optional and not enforced by default. In practice, users may call `addr2cidr` or `cidrlookup` with untrusted input and without validation, incorrectly assuming that this is safe.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | libnet-cidr-perl | no fix listed | DEBIAN-CVE-2021-4456 |
| Debian:13 | libnet-cidr-perl | 0.25-1 | DEBIAN-CVE-2021-4456 |
| Debian:14 | libnet-cidr-perl | 0.25-1 | DEBIAN-CVE-2021-4456 |
| Ubuntu:22.04:LTS | libnet-cidr-perl | 0.21-1ubuntu0.2 | UBUNTU-CVE-2021-4456 |
| Ubuntu:24.04:LTS | libnet-cidr-perl | 0.21-2ubuntu0.2 | UBUNTU-CVE-2021-4456 |
Affected products (as reported)
Weakness: CWE-704 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N