Predictive Vulnerability Intelligence.

Product

  • Product
  • Pricing
  • Documentation

Company

  • About
  • Partnerships
  • Blog
  • Support

Legal

  • Terms
  • Privacy
  • Data Licensing

© 2026 FAUCET Technologies LLC. All rights reserved.

CVE-2021-3773

33
FAUCET Score

CVE-2021-3773 is a critical vulnerability in netfilter, affecting products like Fedora, Linux, Oracle, and Red Hat. This flaw allows a network-connected attacker to infer OpenVPN connection endpoint information, which can then be leveraged for further traditional network attacks. With a CVSS score of 9.8 (CRITICAL), the vulnerability has a low attack complexity and can lead to high impact on confidentiality, integrity, and availability. While there is no known active exploitation, public exploit code, or KEV entry, the vulnerability has garnered some community discussion and media coverage, indicating awareness within the cybersecurity landscape.

Impacted Technologies

VendorProductVersion(s)CPE
< 5.14CPE matchmatch criteria
cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
>= 5.15, < 5.15.15CPE matchmatch criteria
cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
34CPE matchmatch criteria
cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*
6.0CPE matchmatch criteria
cpe:2.3:o:redhat:enterprise_linux:6.0:*:*:*:*:*:*:*
7.0CPE matchmatch criteria
cpe:2.3:o:redhat:enterprise_linux:7.0:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

9.8CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
HIGH
Exploitability Score
3.9
Impact Score
5.9
CvssVersion
3.1

Exploit Intelligence

EPSS Score
5.28%
Probability of exploitation in next 30 days
EPSS Percentile
91.7%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0528 is in the 86th percentile among its peer group of 36,897 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.3 Bluesky, 0.3 Mastodon, and 2.4 GitHub mentions.

Media Mentions

The average CVE in this peer group has 0.3 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (5)

microsoftpatch availablevia msrc
Product: 17936-16820Fixed in: 5.10.189.1-1
microsoftpatch availablevia msrc
Product: cm1 kernel 5.10.189.1-1 on CBL Mariner 1.0Fixed in: 5.10.189.1-1
oraclepatch availablevia nvd_reference
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8Fixed in: kernel-rt-0:4.18.0-372.9.1.rt7.166.el8
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8Fixed in: kernel-0:4.18.0-372.9.1.el8
View patch

Vendor Advisories (2)

microsoft2022-Feb/CVE-2021-3773Critical

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

Feb 8, 2022
redhatCVE-2021-3773Moderate

kernel: lack of port sanity checking in natd and netfilter leads to exploit of OpenVPN clients

Sep 8, 2021

References

security.netapp.com / advisory/ntap-20250328-0004
bugzilla.redhat.com / show_bug.cgi
Issue TrackingThird Party Advisory
citizenlab.ca / 2024/07/vulnerabilities-in-vpns-paper-presented-at-the-privacy-enhancing-technologies-symposium-2024
oracle.com / security-alerts/cpujul2022.html
PatchThird Party Advisory