# CVE-2026-73437: Arista EOS DHCP relay source validation bypass

Source: https://junglewise.ai/threats/cve-2026-73437-arista-eos-dhcp-relay-source-validation-bypass  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-15. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-73437 · Severity: critical · CVSS 9.6 · Published 2026-09-15

Arista EOS switches with DHCP relay enabled are vulnerable to spoofed DHCP replies from unauthorized servers. An attacker can send crafted DHCP packets that the relay forwards to clients without validating the source, allowing the attacker to inject malicious network configuration (like rogue DNS or gateway settings). This could redirect traffic, intercept communications, or cause service outages for networked devices.

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

## Quick answers

**Is CVE-2026-73437 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-73437 being exploited in the wild.

**How severe is CVE-2026-73437?** Critical severity, with a CVSS score of 9.6, published 15 September 2026.

**Which products and versions are affected?** Arista Eos 4.33.9M and below (4.33.x), 4.34.7.1M and below (4.34.x), 4.35.5M and below (4.35.x), 4.36.1F and below (4.36.x), and all prior releases.

**Is there a fix for CVE-2026-73437?** 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-2026-73437 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-73437?** 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

The vulnerability is an insufficient data authenticity verification (CWE-345) in the DHCP relay agent. When DHCP relay is configured with helper addresses, the relay forwards DHCP reply packets (DHCPOFFER, DHCPACK, DHCPv6 Relay-Reply) to clients without validating that the source IP matches a configured helper/destination address. An unauthenticated attacker with network access can send spoofed DHCP replies from arbitrary IP addresses; the relay will forward these replies, allowing the attacker to supply malicious DHCP options. Affected EOS versions include 4.36.1F and below (4.36.x), 4.35.5M and below (4.35.x), 4.34.7.1M and below (4.34.x), 4.33.9M and below (4.33.x), and all earlier releases. The vulnerability requires DHCP relay to be actively configured with at least one IPv4 or IPv6 helper address; patches and source-address validation configuration are available.

## Affected products

- Arista EOS 4.33.9M and below (4.33.x), 4.34.7.1M and below (4.34.x), 4.35.5M and below (4.35.x), 4.36.1F and below (4.36.x), and all prior releases

## Timeline

- 2026-09-09: disclosed: Arista Security Advisory 0156 initial release
- 2026-09-15: other: CVE-2026-73437 published

## References

- [https://www.arista.com/en/support/advisories-notices/security-advisory/24712-security-advisory-0156](https://www.arista.com/en/support/advisories-notices/security-advisory/24712-security-advisory-0156)

## 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)