EOS: Unprotected Alternate Channel
CVE-2026-121290 is a high-severity unprotected alternate channel vulnerability in EOS from Arista Networks, with a CVSS 3.1 base score of 8.2 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists versions 4.33.0F, 4.32.0F as the first without the flaw, so updating EOS to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.36% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update EOS to 4.33.0F or 4.32.0F, whichever matches your release line, or a later version.
- Read the advisory on arista.com for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Arista Networks | EOS | 4.36.0F through 4.36.2F; 4.35.0F through 4.35.6M; 4.34.0F through 4.34.8M; 4.33.0F through 4.33.10M; 4.32.0F up to, but not including, 4.33.0F; 1.0.0 up to, but not including, 4.32.0F | 4.33.0F, 4.32.0F |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- NoneNo data is disclosed.
- Integrity
- LowLimited modification of data is possible.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H. Scored by CNA (arista.com).
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 8.3 | High | CNA (arista.com) |
| CVSS 3.1 | 8.2 | High | CNA (arista.com) |
Official description
On affected platforms running Arista EOS with Border Gateway Protocol (BGP) changing the BGP listen port from its default value disables default protective Access Control List (ACL) rules against unexpected BGP peering attempts.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Unprotected Alternate Channel
The product protects a primary channel, but it does not use the same level of protection for an alternate channel.
How developers prevent this class of flaw
- Identify all alternate channels and use the same protection mechanisms that are used for the primary channels.
More Unprotected Alternate Channel vulnerabilities (CWE-420)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Other vulnerabilities in EOS
- 7.5 High severity
- 8.6 High severity
- 8.6 High severity
- 9.6 Critical severity
- 8.6 High severity
- 8.2 High severity
Recent Unprotected Alternate Channel vulnerabilities
- 7.8 High severity
- 7.5 High severity
- 8.8 High severity
- 9.8 Critical severity
- 8.0 High severity
- 8.8 High severity
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