CVE-2026-121289 PUBLISHED

Security Advisory 0208

Assigner: Arista
Reserved: 03.11.2026 Published: 10.11.2026 Updated: 10.11.2026

On affected platforms running Arista EOS with BGP configured, a specially crafted packet can cause the BGP agent to crash.

Successful exploitation causes the BGP agent process to terminate, resulting in the loss of all BGP sessions on the affected device and possible disruption to network routing until the process recovers. Due to the nature of the vulnerability, it may also be possible for a sophisticated attacker to achieve arbitrary code execution, which could compromise the confidentiality and integrity of the affected system.

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CVSS Score: 9.8

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

CVSS 3.1

CVSS Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
CVSS Score: 9.3

Exploitability Metrics		Vulnerable System Impact Metrics		Subsequent System Impact Metrics
Attack Vector	Network	Confidentiality	High	Confidentiality	None
Attack Complexity	Low	Integrity	High	Integrity	None
Attack Requirements	None	Availability	High	Availability	None
Privileges Required	None
User Interaction	None

CVSS 4.0

Product Status

Vendor	Arista Networks
Product	EOS
Versions	Default: unaffected affected from 4.36.0F to 4.36.2F (incl.) affected from 4.35.0F to 4.35.6M (incl.) affected from 4.34.0F to 4.34.8M (incl.) affected from 4.33.0F to 4.33.10M (incl.) affected from 4.25.1F to 4.33.0F (excl.)

Affected Configurations

switch>show ip bgp summary BGP summary information for VRF default Router identifier 10.0.0.1, local AS number 65000 Neighbor Status Codes: m - Under maintenance Neighbor V AS MsgRcvd MsgSent InQ OutQ Up/Down State PfxRcd PfxAcc 10.0.0.2 4 65001 100 100 0 0 01:00:00 Estab 10 10

switch>show running-config all | inc service routing protocols service routing protocols model multi-agent

Workarounds

For BGP sessions that do not rely on the Tunnel Encapsulation Attribute, a workaround is to remove all received Tunnel Encapsulation Attributes by configuring attribute discard, for example:

neighbor default received attribute discard 23

Alternatively, a recommended mitigation to reduce exposure to this vulnerability is to configure BGP peer authentication using TCP-AO in order to ensure that only authorized peers can establish a BGP session.

Credits

This issue was reported to Arista by Joshua Foote of JP Morgan Chase. reporter

References

https://www.arista.com/en/support/advisories-notices/security-advisory/25030-security-advisory-0208

Problem Types

CWE-121 Stack-based Buffer Overflow CWE

Impacts

CAPEC-100 Overflow Buffers