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Fencer Vulns
medium 6.5

CVE-2021-4456 json

Net::CIDR versions before 0.24 for Perl mishandle leading zeros in IP CIDR addresses, which may have unspecified impact

published 2026-02-27 8 mo ago modified 2026-06-17 4 mo ago also EUVD-2021-34770

cvss
6.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 31%
public exploits
0
none known

Summary

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.

Patch / fix

  • MRSAM Net::CIDR 0.24
  • libnet-cidr-perl Debian 14, Debian 13 0.25-1

debian advisories DEBIAN-CVE-2021-4456

  • libnet-cidr-perl Ubuntu 22.04 LTS 0.21-1ubuntu0.2
  • libnet-cidr-perl Ubuntu 24.04 LTS 0.21-2ubuntu0.2
  • libnet-cidr-perl Ubuntu Pro 14.04 LTS 0.17-1ubuntu0.14.04.1~esm2
  • libnet-cidr-perl Ubuntu Pro 16.04 LTS 0.17-1ubuntu0.16.04.1~esm2
  • libnet-cidr-perl Ubuntu Pro 18.04 LTS 0.18-1ubuntu0.1~esm2
  • libnet-cidr-perl Ubuntu Pro 20.04 LTS 0.20-1ubuntu0.1~esm2

ubuntu advisories UBUNTU-CVE-2021-4456

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • perl-Net-CIDR openSUSE Tumbleweed 0.270.0-2.1

opensuse advisories openSUSE-SU-2026:10756-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-4456 updated cvss 7.2

Net-CIDR: mishandling of leading zeros in IP CIDR addresses

  • Red Hat All currently supported Red Hat products
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
yes
Technical impact
partial
Assessed
8 mo ago

Exploit prediction

0.37% chance of exploitation in the next 30 days, higher than 31% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CISA ADP 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
CNA 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

Affected products

  • MRSAM Net::CIDR

Classification

Weakness
  • CWE-704 Incorrect Type Conversion or Cast

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.