CVE-2021-28511Network attack vector

Security ACL bypass via overlapping NAT permit

Published Aug 5, 2022 · Updated Jun 2, 2026

Improper access control in Arista EOS allows remote attackers to bypass security ACL drop rules through overlapping NAT permit rules. When a packet matches both an overlapping NAT ACL permit rule and a security ACL drop rule, EOS forwards the packet instead of enforcing the drop. Exploitation requires dynamic or static NAT on an affected 720XP, 7050X3, or 7300X3 switch and overlapping address ranges; the result is unauthorized forwarding, with no vendor-reported confidentiality or availability impact.

CVSS severity5.8
Medium
EPSS probability0.57%
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 allows remote attackers to bypass security ACL drop rules through overlapping NAT permit rules. When a packet matches both an overlapping NAT ACL permit rule and a security ACL drop rule, EOS forwards the packet instead of enforcing the drop. Exploitation requires dynamic or static NAT on an affected 720XP, 7050X3, or 7300X3 switch and overlapping address ranges; the result is unauthorized forwarding, with no vendor-reported confidentiality or availability impact.

The record

CVE
CVE-2021-28511
Published
Aug 5, 2022
Updated
Jun 2, 2026
Vendor
Arista Networks
Product
Arista EOS
Classifications
CWE-284
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 5, 2022CVE publishedPublication date reported by the CVE source.
  2. Jun 2, 2026Record 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=4.24.0 <=4.24.9
  2. Affected versionversion=4.25.0 <=4.25.8
  3. Affected versionversion=4.26.0 <=4.26.5
  4. Affected versionversion=4.27.0 <=4.27.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Arista Networks · Arista EOSversion=4.24.0 <=4.24.9; version=4.25.0 <=4.25.8; version=4.26.0 <=4.26.5; version=4.27.0 <=4.27.3

Published CVSS scores

5.8Arista NetworksCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N
6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 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

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

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Your stack

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