# CVE-2026-121368: Arista EOS BFD authentication out-of-bounds write

Source: https://junglewise.ai/threats/cve-2026-121368-on-affected-platforms-running-arista-eos-with-bidirectional  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-11-10. Updated: 2026-11-10  
License: CC BY 4.0 with a link back

CVE-2026-121368 · Severity: high · CVSS 8.6 · Published 2026-11-10

Arista EOS network switches running Bidirectional Forwarding Detection (BFD) with MD5 or SHA1 authentication are vulnerable to denial of service attacks. An attacker with network access adjacent to a BFD-enabled interface can send a specially crafted packet that causes the switch to crash and reboot, disrupting network connectivity and services.

Technologies: [Arista Eos](https://junglewise.ai/threats/technologies/eos). Vendors: [Arista](https://junglewise.ai/threats/vendors/arista).

## Quick answers

**Is CVE-2026-121368 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-121368 being exploited in the wild.

**How severe is CVE-2026-121368?** High severity, with a CVSS score of 8.6, published 10 November 2026.

**Which products and versions are affected?** Arista Eos 4.36.2F and below in 4.36.x; 4.35.6M and below in 4.35.x; 4.34.8M and below in 4.34.x; 4.33.10M and below in 4.33.x; all 4.32.x; 4.22.0 through end of support.

**Is there a fix for CVE-2026-121368?** No fixed version is recorded yet. Disable BFD authentication for MD5 or SHA1 if not required, or replace with a more secure authentication mechanism such as SHA256. Restrict network access to BFD-enabled interfaces to trusted adjacent peers only. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-121368 attacked?** It is attacked over the network or from the adjacent network, in a network appliance.

**Am I affected by CVE-2026-121368?** Check whether you run Arista Eos at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix


Disable BFD authentication for MD5 or SHA1 if not required, or replace with a more secure authentication mechanism such as SHA256. Restrict network access to BFD-enabled interfaces to trusted adjacent peers only.

## Technical details

An out-of-bounds write vulnerability (CWE-787) in the BFD authentication handler allows unauthenticated attackers with network adjacency (direct or multi-hop) to trigger a system crash via a specially crafted BFD packet. The vulnerability exists only when BFD is configured to use keyed MD5 or SHA1 authentication. The attack requires no user interaction and can be exploited without prior authentication, but depends on the specific configuration being in place.

## Affected products

- Arista EOS 4.36.2F and below in 4.36.x; 4.35.6M and below in 4.35.x; 4.34.8M and below in 4.34.x; 4.33.10M and below in 4.33.x; all 4.32.x; 4.22.0 through end of support

## Timeline

- 2026-11-10: disclosed

## References

- [https://www.arista.com/en/support/advisories-notices/security-advisory/25028-security-advisory-0206](https://www.arista.com/en/support/advisories-notices/security-advisory/25028-security-advisory-0206)

## Related threats

- [Arista EOS path traversal in eAPI service](https://junglewise.ai/threats/cve-2026-121371-on-affected-eos-versions-with-the-eapi-service-enabled-a)
- [Arista EOS denial of service in PTP](https://junglewise.ai/threats/cve-2026-121370-on-affected-platforms-running-arista-eos-with-precision-time)
- [Arista EOS denial of service via resource exhaustion](https://junglewise.ai/threats/cve-2026-121369-on-affected-platforms-running-arista-eos-under-specific-link)
- [Arista EOS RIPv2 silent enablement on management interfaces](https://junglewise.ai/threats/cve-2026-121367-on-affected-arista-eos-platforms-with-routing-information)
- [Arista EOS kernel crash via crafted S-BFD PDU](https://junglewise.ai/threats/cve-2026-121295-on-affected-platforms-running-arista-eos-configured-as-s-bfd)