CVE-2021-3773

CRITICALNVD 9.89.8—
EchelonGraph scoreMEDIUM confidence

Score 9.8 from GitHub Security Advisory (severity: CRITICAL) published 2022-02-17. NVD baseline CVSS 9.8; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
9.8
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 5%CVSS: 9.8Exploit: NoneExposed: 0

A fix is available — apply it.

A flaw in netfilter could allow a network-connected attacker to infer openvpn connection endpoint information for further use in traditional network attacks.

CVSS v3
9.8
EG Score
9.8(medium)
EG Risk
61(Track)
EG Risk 61/100SSVC: 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
Severity98% × 45%
Exploitation5% × 40%
Automatability100% × 15%
Action: Routine — remediate on your standard cadence.
EPSS
91.7%
KEV
Not listed

Published

February 16, 2022

Last Modified

March 28, 2025

Advisory Details (3)

Auto-updated Jul 6, 2026
Patch available. Sources: redhat.
generic

NetApp Product Security

https://security.netapp.com/advisory/ntap-20250328-0004/
generic

Vulnerabilities in VPNs: Paper presented at the Privacy Enhancing Technologies Symposium 2024 - The Citizen Lab

https://citizenlab.ca/2024/07/vulnerabilities-in-vpns-paper-presented-at-the-privacy-enhancing-technologies-symposium-2024/
redhat Patch Available

2004949 – (CVE-2021-3773) CVE-2021-3773 kernel: lack of port sanity checking in natd and netfilter leads to exploit of OpenVPN clients

Affected: Red Hat Enterprise Linux 8

https://bugzilla.redhat.com/show_bug.cgi?id=2004949

Vendor Advisories for CVE-2021-3773(2)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Patch Availability(2)

Vendor / EcosystemFixed in / PatchReleasedSource
redhatkernel-rt-0:4.18.0-372.9.1.rt7.166.el82022-05-10redhat
redhatkernel-0:4.18.0-372.9.1.el82022-05-10redhat

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Weakness Classification(1)

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

Additional Vendor Advisories

(1)

Vendors that published advisories for this CVE beyond the curated set above. Broader coverage but minimal per-row detail — click through for the original advisory.

Data Freshness Timeline

(refreshed 12× in last 7d / 45× 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. 2026-07-23 02:03 UTCEG score recompute
  2. 2026-07-22 22:49 UTCEG score recompute
  3. 2026-07-22 14:06 UTCEPSS rescore
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  72. 2026-05-26 02:55 UTCVendor advisory
  73. 2026-05-26 02:55 UTCGHSA enrichment

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Frequently asked(5)

What is CVE-2021-3773?
CVE-2021-3773 is a critical vulnerability published on February 16, 2022. A flaw in netfilter could allow a network-connected attacker to infer openvpn connection endpoint information for further use in traditional network attacks.
When was CVE-2021-3773 disclosed?
CVE-2021-3773 was first published in the National Vulnerability Database on February 16, 2022, with the most recent update on March 28, 2025. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-3773 actively exploited?
CVE-2021-3773 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 91.7% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2021-3773?
CVE-2021-3773 has a CVSS v3 base score of 9.8 (NVD).
How do I remediate CVE-2021-3773?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-3773, 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.

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