Security readout for executives and security teams
Plain-English summary
CVE-2021-28511 is an Arista EOS ACL bypass issue. In affected configurations, traffic that should be blocked by a Security ACL may be forwarded if it also matches a NAT ACL permit rule. The business risk is unintended network access across controls that operators expect to enforce segmentation.
Executive priority
Treat this as a moderate network-control integrity issue. Prioritize environments using affected Arista EOS versions for segmentation, boundary filtering, or regulated network separation, especially where NAT and Security ACLs overlap.
Technical view
Arista describes an internally found EOS flaw where NAT ACL permit matching can override the intended Security ACL drop behavior for the same packet flow. The CVSS 3.1 score is 5.8 with network attack vector, low complexity, no privileges, no user interaction, scope changed, and low integrity impact.
Likely exposure
Exposure is limited to Arista EOS versions listed in the bundle: 4.24.0, 4.25.0, 4.26.0, and 4.27.0. Practical exposure depends on configurations where NAT ACL permit rules overlap traffic ranges denied by Security ACLs.
Exploitation context
The bundle does not show CISA KEV listing or cited evidence of active exploitation. The described condition is configuration-dependent and could allow forwarding that violates intended ACL policy, but the provided sources do not prove public exploit activity.
Researcher notes
The evidence supports an ACL precedence or enforcement failure involving NAT ACL permit and Security ACL drop logic. The source bundle does not include fixed versions, workarounds, affected hardware scope, or exploit telemetry, so remediation details should be confirmed against the Arista advisory.
Mitigation direction
- Review the Arista advisory for affected and fixed EOS release guidance.
- Upgrade or apply vendor-recommended remediation once confirmed from Arista guidance.
- Remove overlap between NAT ACL permit filters and Security ACL denied ranges where feasible.
- Add upstream or downstream enforcement for denied traffic until EOS remediation is confirmed.
Validation and detection
- Inventory Arista EOS devices running 4.24.0, 4.25.0, 4.26.0, or 4.27.0.
- Review NAT ACL permit filters for overlap with Security ACL drop rules.
- Validate policy enforcement in an authorized test environment without exposing production paths.
- Check flow telemetry for traffic forwarded despite matching denied Security ACL ranges.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-284: Authorization and privilege behavior lookup
Authorization weaknesses can support privilege escalation and valid-account review, depending on exploit path. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2021-28511 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Medium
- CVSS
- 5.8 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
SSVC decision data
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N3.91.4AristaVulnerability scoring details
Base CVSS 3.1 score
5.8MediumVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
- CVE publishedCVE Program
The CVE record was published.
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
Source materials
- CVE List V5 sourceCVE List V5
- https://www.arista.com/en/support/advisories-notices/security-advisory/15862-security-advisory-0078CVE reference, Arista · x_refsource_MISC
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Improper Access Control
Improper Access Control represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.