CVE-2021-3773

highpriority · attend · 51EPSS 0.053 · 93 %ileexploit · PoCEURUUS

grimoire priorityP1 · Urgent

Exploitable?

Public exploit

1 exploit · PoC

Likely / severe?

5.28% (93rd) EPSS

CVSS 7.5 · high

Is it mine?

12 products

Check your exposure

Who says so?

4 sources

cnnvd · enisa_euvd · fstec_bdu · nvd

EPSS · scored 2026-10-27

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

cvss

Technical severity, 0–10. One row per scoring source.

9.8

010

base score 0–10 · higher = more severe · hover a vector to decode⚠ sources disagree · high–critical · 7.5–9.8

v2.07.5highAV:N/AC:L/Au:N/C:P/I:P/A:Pprimary · NVD / NIST USexploitability 10 · impact 6.4

v3.19.8criticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hprimary · NVD / NIST USexploitability 3.9 · impact 5.9

v3.19.8criticalAV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsecondary · FSTEC (BDU) RU

v3.19.3criticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H/E:Psecondary · CVSS-BT (t0sche)

ssvc

A stakeholder decision — act, attend, or track — from exploitation and impact.

Exploitation: none · Automatable: yes · Technical Impact: totalcoordinatorcisa_ssvcUS

weaknesses

The CWE weakness classes this flaw belongs to.

CWE-200USCWE-200US

exploits (1)

Public proof-of-concept and weaponised exploit code.

d0rb/CVE-2021-3773This script exploits the "Port Shadow" vulnerability (CVE-2021-3773) in OpenVPN servers using Netfilter for NAT.PoC · poc_in_github

affected products (12)

Products and version ranges known to be affected.

n/a Kernel≤ kernel 5.14.0-49.el9, kernel 5.15.15-100.fc34, kernel 5.15.15-200.fc35enisa_euvdEU
Red Hat Inc. Red Hat Enterprise Linux≤ 8fstec_bduRU
Сообщество свободного программного обеспечения Linux≥ 2.6.12fstec_bduRU
fedoraproject fedora= 34nvdUScpe:2.3:o:fedoraproject:fedora:*:*:*:*:*:*:*:*
linux linux kernel< 5.14nvdUScpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux kernel5.15 → 5.15.15nvdUScpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
oracle communications cloud native core binding support function= 22.1.3nvdUScpe:2.3:a:oracle:communications_cloud_native_core_binding_support_function:*:*:*:*:*:*:*:*
oracle communications cloud native core network exposure function= 22.1.1nvdUScpe:2.3:a:oracle:communications_cloud_native_core_network_exposure_function:*:*:*:*:*:*:*:*
oracle communications cloud native core policy= 22.2.0nvdUScpe:2.3:a:oracle:communications_cloud_native_core_policy:*:*:*:*:*:*:*:*
redhat enterprise linux= 6.0nvdUScpe:2.3:o:redhat:enterprise_linux:*:*:*:*:*:*:*:*
redhat enterprise linux= 7.0nvdUScpe:2.3:o:redhat:enterprise_linux:*:*:*:*:*:*:*:*
redhat enterprise linux= 8.0nvdUScpe:2.3:o:redhat:enterprise_linux:*:*:*:*:*:*:*:*

also known as (4)

Other names and identifiers for this entity.

sources

Which sources assert this record, and when.

cnnvd enisa_euvd fstec_bdu nvd NVD CVE.org MITRE

published 2022-02-16modified 2026-08-25

references (19)

External citations — patches, advisories, analysis.

scry

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