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CVE-2021-4456

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

6.5 MediumFix available

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.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
Low
Integrity
Low
Availability
None

Exploit likelihood

0.37%Up 0.3 points since Feb 27, 2026
90%50%10%1%

What each source reports

CVE List Score used 6.5

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

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.

Record
CVE-2021-4456
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
Weakness
CWE-704
Updated
2026-11-02
EUVDEUVD-2021-34770 6.5

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.

Record
EUVD-2021-34770
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
Updated
2026-11-02
GitHub AdvisoriesGHSA-6xjh-63ff-92mc 6.5

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

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.

Record
GHSA-6xjh-63ff-92mc
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
Weakness
CWE-704
Updated
2026-11-02
NVD 6.5

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.

Record
CVE-2021-4456
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
Weakness
CWE-704
Updated
2026-11-02
OSV 6.5

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.

Record
CVE-2021-4456
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
Updated
2026-11-02
OSVDEBIAN-CVE-2021-4456 6.5

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.

Record
DEBIAN-CVE-2021-4456
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
Updated
2026-11-02
Show 4 moreShow less
OSVUBUNTU-CVE-2021-4456 6.5

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.

Record
UBUNTU-CVE-2021-4456
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
Updated
2026-11-02
OSVopenSUSE-SU-2026:10756-1 No score

perl-Net-CIDR-0.270.0-2.1 on GA media

These are all security issues fixed in the perl-Net-CIDR-0.270.0-2.1 package on the GA media of openSUSE Tumbleweed.

Record
openSUSE-SU-2026:10756-1
Updated
2026-11-02
OSVopenSUSE-SU-2026:20773-1 No score

Security update for perl-Net-CIDR

This update for perl-Net-CIDR fixes the following issues:

Changes in perl-Net-CIDR:

  • updated to 0.270.0 (0.27) 0.27 Sam Varshavchik cidrvalidate() bug fix.

  • updated to 0.260.0 (0.26) 0.26 Sam Varshavchik cidrvalidate() should accept IPv6 addresses with one uncompressed 0.

  • updated to 0.250.0 (0.25) 0.25 Sam Varshavchik Fix warning with Perl 5.40 0.24.1 No changes, re-pushed due to a release problem. 0.24 2025-03-09 brian d foy

    • Strip leading zeros from octets from addr2cidr bsc#1259024 CVE-2021-4456
  • updated to 0.230.0 (0.23) 0.23 2025-03-09 brian d foy

    • Allow unabbreviated IPv6 addresses. 0.22 2025-03-09 Sam Varshavchik
    • Improve several error messages. 2025-03-09 brian d foy
    • Allow unabbreviated IPv6 addresses.
Record
openSUSE-SU-2026:20773-1
Updated
2026-11-02
OSVUSN-8110-1 No score

libnet-cidr-perl vulnerability

Dave Rolsky discovered that Net-CIDR did not properly sanitize IP addresses. An attacker could possibly use this to bypass IP-based restrictions.

Record
USN-8110-1
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
libnet-cidr-perl
Debian:12
All versions, plus listed versions
0.21-20.23-10.25-10.27-1
None known
libnet-cidr-perl
Debian:13
before 0.25-1
0.25-1
libnet-cidr-perl
Debian:14
before 0.25-1
0.25-1
libnet-cidr-perl
Ubuntu:Pro:14.04:LTS
before 0.17-1ubuntu0.14.04.1~esm2, plus listed versions
0.17-1
0.17-1ubuntu0.14.04.1~esm2
libnet-cidr-perl
Ubuntu:Pro:16.04:LTS
before 0.17-1ubuntu0.16.04.1~esm2, plus listed versions
0.17-1
0.17-1ubuntu0.16.04.1~esm2
libnet-cidr-perl
Ubuntu:Pro:18.04:LTS
before 0.18-1ubuntu0.1~esm2, plus listed versions
0.18-1
0.18-1ubuntu0.1~esm2
libnet-cidr-perl
Ubuntu:Pro:20.04:LTS
before 0.20-1ubuntu0.1~esm2, plus listed versions
0.20-1
0.20-1ubuntu0.1~esm2
libnet-cidr-perl
Ubuntu:22.04:LTS
before 0.21-1ubuntu0.2, plus listed versions
0.20-10.21-1
0.21-1ubuntu0.2
libnet-cidr-perl
Ubuntu:24.04:LTS
before 0.21-2ubuntu0.2, plus listed versions
0.21-2
0.21-2ubuntu0.2
perl-Net-CIDR
openSUSE:Tumbleweed
before 0.270.0-2.1
0.270.0-2.1

History

History
RecordedChangedSources
first indexedCVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2021-4456 is a medium vulnerability (CVSS 6.5) in Mrsam Net::cidr, published February 27, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.37%, the 31st percentile. Fixed in libnet-cidr-perl 0.25-1.

References

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