Networks

CVE-2026-121289

Crafted packet crashes Arista EOS BGP agent, causing session loss and possible RCE.

Major vulnerability. Arista EOS is widely deployed in enterprise and carrier networks; a BGP agent crash with potential RCE can disrupt routing and cause widespread outage or device compromise.

CVSS: 9.3Criticalscored by the publisher (CNA)
Exploited in the wild: Not knownnot in CISA KEV as of our last sync
EPSS: No score yet
Fix: Patch availablesee the advisories in the references
Published: 10 Nov 2026analysed here 12 Nov 2026

Summary

Impact

Remote crafted BGP packet can terminate the BGP agent, dropping all BGP sessions and potentially enabling arbitrary code execution and full device compromise.

Triage

Attack surface: Server-side
Exploitable: At runtime
Attack vector: network
Weakness: CWE-121 Stack-Based Buffer Overflow
Can a WAF block it?: No. See why

The summary, impact and action text on this page are written by our AI analysis pipeline, or taken from the NVD description when a CVE was imported from NVD. They are not the vendor's wording: check them against the sources. A longer AI executive summary and technical analysis are generated for signed-in accounts on the Max plan.

Affected products

Product	Affected versions	Vendor says fixed in
Arista Networks EOS	>= 4.36.0F and <= 4.36.2F>= 4.35.0F and <= 4.35.6M>= 4.34.0F and <= 4.34.8M>= 4.33.0F and <= 4.33.10M>= 4.25.1F and < 4.33.0FVendor says fixed in: not stated	Not stated by the vendor

As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.

Products named in our analysis

Arista EOS devices with BGP enabled

Fix and mitigation

Action required

Immediate action required

WAF and other mitigations

Can a WAF block it? No. This is a stack buffer overflow. Generic WAF rules do not recognise the input that triggers it; only a rule written for this specific CVE can, and only if the triggering request has a recognisable shape.

Also consider: patch

Based on the weakness type only; no CVE-specific evidence yet. We check Cloudflare, AWS, Google Cloud Armor and Azure; for Akamai, Imperva, Fastly, F5, ask your vendor.

Remediation steps (AI-written)

Step-by-step remediation is generated for accounts on the Max plan, for CVEs that match a technology in their stack. Add this technology to your stack to see the fix checklist.

Exploitation evidence

CISA KEV catalog: Not listed as of our last sync.
Public exploit code: None on record in Exploit-DB, Metasploit, Nuclei templates or PoC-in-GitHub.

Timeline

10 Nov 2026Published
10 Nov 2026CVE record last updatedsame day later
12 Nov 2026Analysed by vulneraibility.com2 days later

Common questions

Is CVE-2026-121289 being exploited?

Not confirmed. CVE-2026-121289 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked.

How severe is CVE-2026-121289?

CVE-2026-121289 is rated Critical with a CVSS score of 9.3. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.

Is there a patch for CVE-2026-121289?

Yes. A fix has been recorded for CVE-2026-121289. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.

What does CVE-2026-121289 affect?

CVE-2026-121289 affects Arista EOS devices with BGP enabled. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.

What should I do about CVE-2026-121289?

Apply vendor advisories/patches ASAP; restrict BGP peers, filter/inspect BGP traffic, and monitor sessions.

Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.

References

NVD CVE.org CVE Details Source

1 reference in the CVE record, grouped by the tags the record gives them.

Advisories (1)

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

Where the data on this page comes from

CVE List (CVE.org): description, affected versions, references; CVE Terms of Use
NVD: CVSS and CPE data
FIRST EPSS: exploit probability and percentile

Summary, impact and triage tags: written by our AI analysis pipeline from the sources above. Check them against the sources.

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