CVE-2021-4456 Net::CIDR versions before 0.24 for Perl mishandle leading zeros in IP CIDR addresses, which may have unspecified impact
Attackers can bypass IP-based access controls by exploiting leading zero mishandling in Net::CIDR Perl library functions.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2021-4456?
CVE-2021-4456 is a medium-severity vulnerability in MRSAM Net::CIDR, published on 27 Feb 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
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.
Weakness: CWE-704
Which versions are affected by CVE-2021-4456?
It affects 1 product.
Linux distribution packages (1)
perl-Net-CIDR openSUSE:Tumbleweed | All versions | 0.270.0-2.1 |
Products include Mrsam Net\.
How do I fix CVE-2021-4456?
Upgrade to a fixed version.
Is CVE-2021-4456 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-4456 exists.
Sources
Also known as DEBIAN-CVE-2021-4456, GHSA-6xjh-63ff-92mc, UBUNTU-CVE-2021-4456, USN-8110-1, openSUSE-SU-2026:10756-1, openSUSE-SU-2026:20773-1.