# CVE-2026-121288: Arista EOS RIPv2 MD5 authentication bypass

Source: https://junglewise.ai/threats/cve-2026-121288-an-unauthenticated-attacker-on-an-adjacent-network-segment-can  
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-2026-121288 · Severity: high · CVSS 8.1 · Published 2026-11-10

Arista EOS switches use RIPv2, a protocol that manages routing tables on networks, to communicate with neighboring devices about available routes. An attacker on the same network segment can forge RIP route updates to bypass MD5 authentication if it is enabled, causing the switch to install malicious routes that redirect traffic through attacker-controlled paths, create routing loops, or drop traffic entirely. This disrupts network connectivity and can isolate critical network segments.

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

## Quick answers

**Is CVE-2026-121288 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-121288 being exploited in the wild.

**How severe is CVE-2026-121288?** High severity, with a CVSS score of 8.1, published 10 November 2026.

**Which products and versions are affected?** Arista Eos 4.37.0F, 4.36.2F and below (4.36.x), 4.35.6M and below (4.35.x), 4.34.8M and below (4.34.x), 4.33.10M and below (4.33.x), all 4.32.x.

**Is there a fix for CVE-2026-121288?** No fixed version is recorded yet. Check the vendor's advisory in the references below. 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-2026-121288 attacked?** It is attacked from the adjacent network, in a network appliance.

**Am I affected by CVE-2026-121288?** 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.

## Technical details

An unauthenticated attacker on an adjacent network segment can inject crafted RIPv2 packets that bypass MD5 authentication on affected interfaces, exploiting incorrect implementation of the authentication algorithm (CWE-303). Exploitation requires RIP to be enabled and MD5 authentication to be configured on an interface; a successful attack allows injection of unauthorized route updates that redirect traffic or create service disruptions. The vulnerability affects EOS versions 4.37.0F and earlier in multiple release trains.

## Affected products

- Arista EOS 4.37.0F, 4.36.2F and below (4.36.x), 4.35.6M and below (4.35.x), 4.34.8M and below (4.34.x), 4.33.10M and below (4.33.x), all 4.32.x

## Timeline

- 2026-11-10: disclosed
- 2026-11-10: advisory

## References

- [https://www.arista.com/en/support/advisories-notices/security-advisory/25043-security-advisory-0221](https://www.arista.com/en/support/advisories-notices/security-advisory/25043-security-advisory-0221)

## 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 BFD authentication out-of-bounds write](https://junglewise.ai/threats/cve-2026-121368-on-affected-platforms-running-arista-eos-with-bidirectional)
- [Arista EOS RIPv2 silent enablement on management interfaces](https://junglewise.ai/threats/cve-2026-121367-on-affected-arista-eos-platforms-with-routing-information)