Critical · CVSS 9.3CVE-2026-121289

Security Advisory 0208CVE-2026-121289

Answer in brief

CVE-2026-121289 records a Critical severity (CVSS 9.3) vulnerability in Security Advisory 0208. The current sources do not mark it as known exploited. The current feed maps Arista Networks/EOS (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Nov 10, 2026Updated Nov 10, 2026Source checked Nov 10, 2026First seen by HOL Nov 10, 2026Material review Nov 10, 2026

Upstream Advisory

Key facts

Risk: Critical · CVSS 9.3
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Not reported

Why this deserves its current priority

CVSS is 9.3. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Arista Networks/EOS (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Arista Networks/EOSgeneric	>=4.36.0F <=4.36.2F \|\| >=4.35.0F <=4.35.6M \|\| >=4.34.0F <=4.34.8M \|\| >=4.33.0F <=4.33.10M \|\| >=4.25.1F <4.33.0F	Not reported

Recommended response

Check inventory. Check lockfiles and deployed manifests for Arista Networks/EOS.
Review the reported fix. Source-reported workaround: 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.

Evidence timeline and material changes

Published upstream
Nov 10, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Nov 10, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Nov 10, 2026

Sources and claim methodology

Source referencearista.com

Upstream source description

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.

Quoted source text, attributed separately from HOL analysis.

Affected scope and exposure questions

The current feed maps Arista Networks/EOS (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Arista Networks/EOSgeneric	>=4.36.0F <=4.36.2F \|\| >=4.35.0F <=4.35.6M \|\| >=4.34.0F <=4.34.8M \|\| >=4.33.0F <=4.33.10M \|\| >=4.25.1F <4.33.0F	Not reported

Recommended response

Check inventory. Check lockfiles and deployed manifests for Arista Networks/EOS.

Review the reported fix. Source-reported workaround: 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.

Sources and claim methodology

Upstream source description

Quoted source text, attributed separately from HOL analysis.