CVE-2021-4456

MEDIUMPre-NVD 6.56.5—
EchelonGraph scoreMEDIUM confidence

Score 6.5 from GitHub Security Advisory published 2026-02-27. CISA-ADP (Vulnrichment) CVSS v3.1 baseline 6.5; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: cisa-adp, epss, ghsa
6.5EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 6.5Exploit: None knownExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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.

CVSS v3
6.5
EG Score
6.5(medium)
EG Risk
34(Track)
EG Risk 34/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity65% × 45%
Exploitation0% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
26%
KEV
Not listed

Published

February 27, 2026

Last Modified

June 17, 2026

Advisory Details (3)

Auto-updated Aug 4, 2026
Upstream fix merged — awaiting tagged release. Sources: github_commit.
generic

ChangeLog - metacpan.org

https://metacpan.org/dist/Net-CIDR/changes
github_commit

commit e3648c6bc6bd (svarshavchik/Net-CIDR)

Fix landed in svarshavchik/Net-CIDR commit e3648c6bc6bd — awaiting tagged release

https://github.com/svarshavchik/Net-CIDR/commit/e3648c6bc6bdd018f90cca4149c467017d42bd10
generic

Security Issues in Perl IP Address distros - House Absolute(ly Pointless)

https://blog.urth.org/2021/03/29/security-issues-in-perl-ip-address-distros/

Affected Packages

(4 across 4 ecosystems)
Debian:11(1)
PackageVulnerable rangeFixed inDependents
libnet-cidr-perl0.20-1 ... 0.27-1 (6 versions)——
Debian:12(1)
PackageVulnerable rangeFixed inDependents
libnet-cidr-perl0.21-2, 0.23-1, 0.25-1, 0.27-1——
Debian:13(1)
PackageVulnerable rangeFixed inDependents
libnet-cidr-perl—0.25-1—
Debian:14(1)
PackageVulnerable rangeFixed inDependents
libnet-cidr-perl—0.25-1—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

All Vendor Advisories

(1)

Every vendor that published an advisory referencing this CVE — pulled from our cve_vendor_advisories aggregation. Click any row for the vendor's original advisory page.

Data Freshness Timeline

(refreshed 7× in last 7d / 27× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-09-19 15:38 UTCEPSS rescore
  2. 2026-09-18 19:24 UTCEPSS rescore
  3. 2026-09-18 19:06 UTCOSV refresh
  4. 2026-09-17 19:23 UTCEPSS rescore
  5. 2026-09-16 14:05 UTCEPSS rescore
  6. 2026-09-16 14:05 UTCEPSS rescore
  7. 2026-09-15 03:06 UTCEPSS rescore
  8. 2026-09-12 14:57 UTCEPSS rescore
  9. 2026-09-11 14:49 UTCEPSS rescore
  10. 2026-09-11 09:33 UTCEPSS rescore
  11. 2026-09-08 21:57 UTCEPSS rescore
  12. 2026-09-06 13:45 UTCEPSS rescore
  13. 2026-09-05 15:25 UTCEPSS rescore
  14. 2026-09-04 13:57 UTCEPSS rescore
  15. 2026-09-04 05:03 UTCEPSS rescore
  16. 2026-09-02 14:09 UTCEPSS rescore
  17. 2026-09-01 13:51 UTCEPSS rescore
  18. 2026-08-30 22:17 UTCOSV refresh
  19. 2026-08-30 19:14 UTCEPSS rescore
  20. 2026-08-30 01:19 UTCEPSS rescore
  21. 2026-08-28 21:38 UTCEPSS rescore
  22. 2026-08-27 14:22 UTCEPSS rescore
  23. 2026-08-26 14:43 UTCEPSS rescore
  24. 2026-08-25 13:46 UTCEPSS rescore
  25. 2026-08-24 14:13 UTCEPSS rescore
Show 53 more
  1. 2026-08-21 23:46 UTCEPSS rescore
  2. 2026-08-20 22:52 UTCEPSS rescore
  3. 2026-08-19 17:01 UTCEPSS rescore
  4. 2026-08-18 13:45 UTCEPSS rescore
  5. 2026-08-17 13:44 UTCEPSS rescore
  6. 2026-08-16 14:53 UTCEPSS rescore
  7. 2026-08-16 02:11 UTCEPSS rescore
  8. 2026-08-15 01:27 UTCEPSS rescore
  9. 2026-08-14 08:52 UTCEG score recompute
  10. 2026-08-14 08:52 UTCVendor advisory
  11. 2026-08-14 08:52 UTCGHSA enrichment
  12. 2026-08-13 21:57 UTCEPSS rescore
  13. 2026-08-13 00:50 UTCEG score recompute
  14. 2026-08-13 00:50 UTCVendor advisory
  15. 2026-08-13 00:50 UTCGHSA enrichment
  16. 2026-08-12 13:48 UTCEPSS rescore
  17. 2026-08-11 13:38 UTCEPSS rescore
  18. 2026-08-11 07:41 UTCEG score recompute
  19. 2026-08-11 07:41 UTCVendor advisory
  20. 2026-08-11 07:41 UTCGHSA enrichment
  21. 2026-08-10 08:32 UTCEG score recompute
  22. 2026-08-10 08:32 UTCVendor advisory
  23. 2026-08-10 08:32 UTCGHSA enrichment
  24. 2026-08-09 13:44 UTCEPSS rescore
  25. 2026-08-09 08:30 UTCEG score recompute
  26. 2026-08-09 08:30 UTCVendor advisory
  27. 2026-08-09 08:30 UTCGHSA enrichment
  28. 2026-08-08 16:34 UTCEPSS rescore
  29. 2026-08-07 20:33 UTCEG score recompute
  30. 2026-08-07 20:33 UTCVendor advisory
  31. 2026-08-07 20:33 UTCGHSA enrichment
  32. 2026-08-07 16:24 UTCEPSS rescore
  33. 2026-08-06 13:44 UTCEPSS rescore
  34. 2026-08-06 02:55 UTCEG score recompute
  35. 2026-08-06 02:55 UTCVendor advisory
  36. 2026-08-06 02:55 UTCGHSA enrichment
  37. 2026-08-05 19:15 UTCEPSS rescore
  38. 2026-08-04 15:06 UTCEPSS rescore
  39. 2026-08-04 10:34 UTCEPSS rescore
  40. 2026-08-04 04:55 UTCEG score recompute
  41. 2026-08-04 04:55 UTCVendor advisory
  42. 2026-08-04 04:55 UTCGHSA enrichment
  43. 2026-08-03 10:33 UTCEPSS rescore
  44. 2026-08-02 19:25 UTCEG score recompute
  45. 2026-08-02 19:25 UTCVendor advisory
  46. 2026-08-02 19:25 UTCGHSA enrichment
  47. 2026-08-02 02:24 UTCEPSS rescore
  48. 2026-08-01 04:13 UTCEPSS rescore
  49. 2026-07-30 16:25 UTCEPSS rescore
  50. 2026-07-30 01:28 UTCEPSS rescore
  51. 2026-07-28 15:33 UTCEPSS rescore
  52. 2026-07-27 14:04 UTCEG score recompute
  53. 2026-07-27 14:04 UTCGHSA enrichment

Frequently asked(5)

What is CVE-2021-4456?
CVE-2021-4456 is a medium vulnerability published on February 27, 2026. 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…
When was CVE-2021-4456 disclosed?
CVE-2021-4456 was first published in the National Vulnerability Database on February 27, 2026, with the most recent update on June 17, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-4456 actively exploited?
CVE-2021-4456 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 74.5% of all scored CVEs.
What is the CVSS score of CVE-2021-4456?
CVE-2021-4456 has a CVSS v3.1 base score of 6.5 (CISA-ADP / Vulnrichment enrichment; NVD's own analysis pending).
How do I remediate CVE-2021-4456?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-4456, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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