dbcve.org
EosOperating system · Arista

CVE-2021-28505

HIGH · 7.5 CVSS v3.1 Published 2022-04-14
Fix available
A fix is available. Upgrade to 4.26.4m / 4.27.1f or later.
See remediation →
84/100
Remediation priority · High
Public exploit Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
On affected Arista EOS platforms, if a VXLAN match rule exists in an IPv4 access-list that is applied to the ingress of an L2 or an L3 port/SVI, the VXLAN rule and subsequent ACL rules in that access list will ignore the specified IP protocol.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis
How this class of weakness works · CWE-284

The application fails to correctly restrict what a user can do or reach, so functions or resources are available to people who should not have them. Attackers simply probe for the paths where the check is missing or wrong. The fix is to enforce access-control decisions consistently on every request, evaluated against the acting user rather than assumed from context.

General guidance for the improper access control class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
EosOperating system
Affected:>= 4.26, < 4.26.4m>= 4.27, < 4.27.1f

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

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

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 4.26.4m / 4.27.1f or later
Fixed in 4.26.4m4.27.1f
Recommended fix High confidence

EOS 4.26.4m or later (for 4.26.x branch); EOS 4.27.1f or later (for 4.27.x branch)

  1. 1. Identify the current EOS version on the affected Arista device using 'show version'
  2. 2. Download the fixed EOS release from the Arista software download portal (reference: www.arista.com)
  3. 3. For devices on EOS 4.26.x branch, upgrade to EOS 4.26.4m or later
  4. 4. For devices on EOS 4.27.x branch, upgrade to EOS 4.27.1f or later
  5. 5. Upload the new EOS image to the device (e.g., copy via SCP/FTP to bootflash:)
  6. 6. Set the boot system to the new image using 'config terminal' then 'boot system <image>'
  7. 7. Save the configuration with 'write memory'
  8. 8. Reload the device to apply the new EOS version
Caveat EOS upgrades may have compatibility considerations; test in a lab environment before production deployment

Generated from the published advisory — verify against the referenced sources before acting.

We can perform the upgrade in your staging environment and verify nothing breaks — typical engagement from $1,950. Get the upgrade done

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-28505 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data