EOS: Incorrect Behavior Order
CVE-2026-121291 is a high-severity incorrect behavior order 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. Affected EOS versions: 4.37.0F; 4.36.0F through 4.36.2F; 4.35.0F through 4.35.6M. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.41% 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
- Check which version of EOS you run against the affected versions below, and install the vendor's latest release.
- 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 | 4.37.0F; 4.36.0F through 4.36.2F; 4.35.0F through 4.35.6M | Not stated |
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
- HighData or code can be modified at will.
- Availability
- LowPerformance or availability is reduced.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:L. 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
A crafted Error Report can leave EOS stuck believing that a cache reset is in progress, preventing ROA publication, withdrawal reconciliation, and BGP origin-validation updates.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Incorrect Behavior Order
The product performs multiple related behaviors, but the behaviors are performed in the wrong order in ways that may produce resultant weaknesses.
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 Incorrect Behavior Order vulnerabilities
- 7.4 High severity
- 7.5 High severity
- 8.0 High severity
- 7.1 High severity
- 7.8 High severity
- 7.4 High severity
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