CVE-2021-3773

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

Published: 2022-02-16 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-3773 is rated High Risk (76/100): CVSS Critical severity, with high exploitation likelihood (EPSS 5.32%, 92th percentile). EPSS ranks this CVE among the most likely to be exploited in the near term. EPSS rose +4.73% over the last day, indicating growing attacker interest. High exploitation likelihood—assess exposure and prioritize remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-3773

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.60% 5.32% +4.73%
2 2026-05-06 0.65% 0.60% -0.06%
3 2026-02-25 — 0.65% —

Full EPSS history (33 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-3773

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
9.8 3.1 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 5.9 [email protected]
7.5 2.0 HIGH
AV:N/AC:L/Au:N/C:P/I:P/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:P)
Partial confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:P)
Partial availability impact.
 10.0 6.4 [email protected]

Weakness enumeration for CVE-2021-3773

OS Trackers for CVE-2021-3773

vendor priority summary link
redhat medium — https://access.redhat.com/security/cve/CVE-2021-3773
suse medium CVE-2021-3773 severity moderate: SUSE including 20 source package names (bpftool-4.18.0-372.9.1.el8, kernel-4.18.0-372.9.1.el8, …), 20 product×package rows across 1 product lines (SUSE Liberty Linux 8): Fixed 20. https://www.suse.com/security/cve/CVE-2021-3773/
ubuntu medium CVE-2021-3773 medium priority: Ubuntu including 168 source packages (linux, linux-allwinner, …), 2111 status rows across 15 suites (bionic, focal, hirsute, impish, jammy, kinetic, lunar, mantic, noble, oracular, plucky, questing, trusty, upstream, xenial): DNE 1649, ignored 301, needs-triage 161. https://ubuntu.com/security/CVE-2021-3773

Affected software / configurations for CVE-2021-3773

Vendor Product Version Raw CPE
linux linux_kernel < 5.14 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 5.15, < 5.15.15 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
fedoraproject fedora 34 cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*
redhat enterprise_linux 6.0 cpe:2.3:o:redhat:enterprise_linux:6.0:*:*:*:*:*:*:*
redhat enterprise_linux 7.0 cpe:2.3:o:redhat:enterprise_linux:7.0:*:*:*:*:*:*:*
redhat enterprise_linux 8.0 cpe:2.3:o:redhat:enterprise_linux:8.0:*:*:*:*:*:*:*
oracle communications_cloud_native_core_binding_support_function 22.1.3 cpe:2.3:a:oracle:communications_cloud_native_core_binding_support_function:22.1.3:*:*:*:*:*:*:*
oracle communications_cloud_native_core_network_exposure_function 22.1.1 cpe:2.3:a:oracle:communications_cloud_native_core_network_exposure_function:22.1.1:*:*:*:*:*:*:*
oracle communications_cloud_native_core_policy 22.2.0 cpe:2.3:a:oracle:communications_cloud_native_core_policy:22.2.0:*:*:*:*:*:*:*

References for CVE-2021-3773

cvelogic Threat Intelligence