# CVE-2024-27891: Arista EOS ACL enforcement failure when using MACsec

Source: https://junglewise.ai/threats/cve-2024-27891-arista-eos-acl-enforcement-failure-when-using-macsec  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-06-04. Updated: 2026-06-04  
License: CC BY 4.0 with a link back

CVE-2024-27891 · Severity: medium · CVSS 5.3 · Published 2026-06-04

A security issue has been identified in Arista EOS where network traffic filters (ACLs) may fail to work correctly on certain hardware. This occurs when both encryption (MACsec) and outbound traffic rules are used on the same network port. As a result, sensitive data that should be blocked might be allowed to leave the network, or legitimate traffic might be unintentionally blocked, potentially bypassing security policies.

## Quick answers

**Is CVE-2024-27891 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2024-27891 being exploited in the wild.

**How severe is CVE-2024-27891?** Medium severity, with a CVSS score of 5.3, published 4 June 2026.

**Which products and versions are affected?** Arista Networks EOS.

**Is there a fix for CVE-2024-27891?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2024-27891 attacked?** It is attacked over the network, in an operating system.

**Am I affected by CVE-2024-27891?** Check whether anything you run is named in the advisory. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A vulnerability in Arista EOS (CWE-284) results in improper access control enforcement when MACsec and egress Access Control Lists (ACLs) are simultaneously configured on the same interface. The root cause is a failure in the hardware or software logic to correctly apply ACL policies to packets as they exit the port. An attacker can potentially bypass intended network restrictions, leading to unauthorized data egress or unintended traffic denial. The issue is reachable via the network without authentication, though it requires a specific configuration state to be present. Users are advised to consult Arista security advisory 0102 for specific platform impact and remediation steps.

## Affected products

- Arista Networks EOS

## Timeline

- 2026-06-04: advisory: Security advisory published by Arista Networks

## References

- [https://www.arista.com/en/support/advisories-notices/security-advisory/19908-security-advisory-0102](https://www.arista.com/en/support/advisories-notices/security-advisory/19908-security-advisory-0102)