CVE-2021-28504Network attack vector

Network access-control bypass via ignored ACL protocols

Published Apr 1, 2022 · Updated Aug 3, 2024

Improper access control in Arista EOS 4.26.0 through 4.26.3M and 4.27.0F allows remote attackers to bypass IPv4 ACL filtering. On affected Strata switches, a VXLAN protocol match in an ingress IPv4 ACL causes the TCAM rule and every later rule to ignore the configured IP-protocol field. The condition requires an enabled TCAM profile and an active ingress ACL containing a VXLAN rule; traffic can then pass under rules intended for other protocols.

CVSS severity7.5
High
EPSS probability0.73%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Improper access control in Arista EOS 4.26.0 through 4.26.3M and 4.27.0F allows remote attackers to bypass IPv4 ACL filtering. On affected Strata switches, a VXLAN protocol match in an ingress IPv4 ACL causes the TCAM rule and every later rule to ignore the configured IP-protocol field. The condition requires an enabled TCAM profile and an active ingress ACL containing a VXLAN rule; traffic can then pass under rules intended for other protocols.

The record

CVE
CVE-2021-28504
Published
Apr 1, 2022
Updated
Aug 3, 2024
Vendor
Arista Networks
Product
Arista EOS
Classifications
CWE-284, CWE-863
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 1, 2022CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=4.26.3F <=4.26.0
  2. Affected versionversion=4.27.0F <=4.27.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Arista Networks · Arista EOSversion=4.26.3F <=4.26.0; version=4.27.0F <=4.27.0

Published CVSS scores

7.5Arista NetworksCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:P/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-284Improper Access Control
CWE-863Incorrect Authorization

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo