CVE-2021-4456

CVE-2021-4456 is a medium-severity vulnerability in Mrsam Net with a CVSS 3.x base score of 6.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-704.

Key facts

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.

Frequently asked questions

What is CVE-2021-4456?
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.
How severe is CVE-2021-4456?
CVE-2021-4456 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2021-4456 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (24th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-4456?
CVE-2021-4456 affects Mrsam Net. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-4456?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2021-4456 have an EU (EUVD) identifier?
Yes. CVE-2021-4456 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2021-34770.
When was CVE-2021-4456 published?
CVE-2021-4456 was published on 2026-02-27 and last updated on 2026-06-17.

References

Affected products (1)

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