VulnerabilityPublished 10 Nov 2026

CVE-2026-121291: Arista Networks EOS · Incorrect Behavior Order

Affects Arista Networks EOSSource CVE Database V5

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Not known to be exploited · CVSS 8.2 High.

Data as of 10 Nov 2026, 20:32 UTC

CVSS 3.1 base score

8.2High

How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none

CVSS scores by source
CNA (Arista)	CVSS 3.1	8.2
CNA (Arista)	CVSS 4.0	8.3

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:L

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: High
Availability: Low

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the impacted component are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 10 Nov 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 10 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
Arista NetworksEOS	Affected >=4.36.0F <=4.36.2F >=4.35.0F <=4.35.6M =4.37.0F	Fixed in–

AI-suggested

Until a fix is available, monitoring for unusual routing behavior related to ROA publication and BGP origin-validation is advisable.

Description

CVE-2026-121291 is a vulnerability in Arista Networks EOS where a crafted Error Report causes the system to incorrectly believe a cache reset is ongoing. This state prevents the publication of ROA, reconciliation of withdrawals, and updates to BGP origin-validation, potentially disrupting routing validation processes.

Impact

The flaw does not impact confidentiality but has a high impact on integrity by preventing proper BGP origin-validation updates and related routing operations. Availability impact is low. This could lead to routing inconsistencies or failures in origin validation, affecting network reliability and security.

Summary

This vulnerability arises from an incorrect behavior order (CWE-696) in Arista EOS. When a specially crafted Error Report is received, EOS remains stuck in a state indicating a cache reset is in progress. This condition blocks critical functions including ROA publication, withdrawal reconciliation, and BGP origin-validation updates, which are essential for maintaining accurate routing information and validation.

References

arista.com/en/support/advisories-notices/security-advisory/25044-security-advisory-0222 (opens in a new tab)

Community reviews

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 10 Nov 2026, 20:32 UTC

WeaknessesCWE-696

Technical details

References

Community reviews

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