CVE-2021-28505Network attack vector

ACL bypass via ignored IP protocol matching

Published Apr 14, 2022 · Updated Sep 16, 2024

Improper access control in Arista EOS 4.26.3M and earlier and 4.27.0F allows remote attackers to bypass IPv4 ACL protocol filters. When a VXLAN rule occurs in an ingress IPv4 ACL, EOS programs that rule and every later rule without enforcing the configured IP protocol field. The issue requires an affected switch with a TCAM profile enabled and such an ACL active on ingress, permitting IP traffic that the ACL was intended to filter.

CVSS severity7.5
High
EPSS probability0.88%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper access control in Arista EOS 4.26.3M and earlier and 4.27.0F allows remote attackers to bypass IPv4 ACL protocol filters. When a VXLAN rule occurs in an ingress IPv4 ACL, EOS programs that rule and every later rule without enforcing the configured IP protocol field. The issue requires an affected switch with a TCAM profile enabled and such an ACL active on ingress, permitting IP traffic that the ACL was intended to filter.

The record

CVE
CVE-2021-28505
Published
Apr 14, 2022
Updated
Sep 16, 2024
Vendor
Arista Networks
Product
Arista EOS
Classifications
CWE-284, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 14, 2022CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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

  1. Affected versionversion=4.26.3M <=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=4.26.3M <=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

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
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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