CVE-2021-4456

Publication date 27 February 2026

Last updated 19 March 2026

Ubuntu priority

Cvss 3 Severity Score

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.

Status

Show unmaintained releases

Package	Ubuntu Release	Status
libnet-cidr-perl	25.10 questing	Not affected
	24.04 LTS noble	Fixed 0.21-2ubuntu0.2
	22.04 LTS jammy	Fixed 0.21-1ubuntu0.2
	20.04 LTS focal	Fixed 0.20-1ubuntu0.1~esm2
	18.04 LTS bionic	Fixed 0.18-1ubuntu0.1~esm2
	16.04 LTS xenial	Fixed 0.17-1ubuntu0.16.04.1~esm2
	14.04 LTS trusty	Fixed 0.17-1ubuntu0.14.04.1~esm2

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Patch details

For informational purposes only. We recommend not to cherry-pick updates. How can I get the fixes?

Package	Patch details
libnet-cidr-perl	Upstream: e3648c6

Severity score breakdown

Parameter	Value
Base score	6.5 · Medium
Attack vector	Network
Attack complexity	Low
Privileges required	None
User interaction	None
Scope	Unchanged
Confidentiality	Low
Integrity impact	Low
Availability impact	None
Vector	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

References

Related Ubuntu Security Notices (USN)

USN-8110-1
Net-CIDR vulnerability
18 March 2026