CVE-2025-8873: Arista EOS IPsec Denial of Service Vulnerability

Technical summary

CVE-2025-8873 affects Arista EOS platforms configured with IPsec. A malformed packet can trigger a denial-of-service condition in the dataplane's IPsec processing pipeline, halting all IPsec traffic forwarding on the affected system. The control plane may detect the stalled pipeline and initiate a reset sequence; however, recovery does not guarantee resumption of traffic forwarding. The vulnerability stems from improper packet validation or state management in the IPsec implementation (CWE-1286: Improper Validation of Specified Quantity in Input). Transit traffic and non-IPsec flows bypass the affected dataplane component and are not impacted. Exploitation requires network-level access to send a specially crafted packet destined for or transiting through the device.

Business impact

Organizations relying on Arista EOS for IPsec-encrypted communications face potential service disruption. An attacker can render IPsec tunnels inoperative on a targeted device with a single malicious packet, interrupting encrypted site-to-site connections, remote access VPNs, or other IPsec-dependent workflows. Unlike a network-wide outage, the impact is confined to IPsec traffic on the compromised device; however, for environments where IPsec is a critical security boundary, this constitutes a high-priority availability and compliance risk. The lack of guaranteed recovery after a reset attempt increases operational complexity and may require manual intervention.

Affected systems

Arista EOS running on platforms with IPsec enabled. The vendor has not disclosed specific EOS versions or hardware models. Organizations should consult Arista's security advisory and verify which platforms and software versions in their environment are susceptible. Non-IPsec configurations are not affected.

Exploitability

The vulnerability requires no authentication, special privileges, or user interaction. Exploitation simply demands network-level access to send a crafted packet to or through the affected device. The CVSS score of 7.5 (High) reflects the low attack complexity and lack of access restrictions. However, practical exploitation may be limited by network segmentation or ingress filtering that prevents external attackers from sending malicious traffic to internal IPsec endpoints. Internal attackers or compromised adjacent systems on the same network segment pose a realistic threat.

Remediation

Arista will issue a patched version of EOS that resolves improper packet validation in the IPsec pipeline. Customers should apply the patch at the earliest opportunity, prioritizing devices on security-critical paths or exposed to untrusted networks. Until patching is feasible, implement network-based mitigations such as ingress filtering, rate limiting on suspected attack vectors, or restricting IPsec endpoints to trusted peer IP ranges. Monitor IPsec session state for unexpected resets or traffic interruptions.

Patch guidance

Consult the official Arista security advisory (linked from the vendor's security page) for the specific EOS version numbers containing the fix. Verify the patch availability for your hardware platform before scheduling maintenance. Test the patch in a non-production environment to confirm IPsec recovery behavior and confirm no regressions in non-IPsec traffic handling. Patch rollout should coordinate with change management and may require a controlled restart of affected devices.

Detection guidance

Monitor Arista EOS syslog and netflow telemetry for abrupt drops in IPsec traffic volume or repeated IPsec pipeline resets without corresponding configuration changes. Inspect packet captures on IPsec interfaces for malformed or anomalous frames preceding traffic loss. Configure alerting on IPsec session state changes, particularly unexpected transitions to "down" or repeated state flapping. Correlate any traffic loss with ingress firewall logs or IDS alerts that may indicate an attack source.

Why prioritize this

This vulnerability scores 7.5 (High) due to unauthenticated network-level exploitability and high availability impact. However, the attack surface is narrower than typical network-facing flaws: the attacker must reach an IPsec endpoint, and non-IPsec functions remain operational. Prioritize patching for Arista devices that terminate IPsec tunnels from untrusted or semi-trusted peers, or that bridge critical encrypted communications. Devices in fully internal networks with strict ingress controls may be deprioritized relative to externally accessible IPsec gateways.

Risk score, explained

CVSS 3.1 vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H yields a base score of 7.5. The 'AV:N' (Attack Vector: Network) and 'AC:L' (Attack Complexity: Low) indicate an attacker can craft and deliver a malicious packet from the network without special conditions. 'PR:N' (no privileges required) and 'UI:N' (no user interaction) confirm the low barrier to exploitation. 'C:N/I:N' (no confidentiality or integrity impact) reflect that this is purely an availability attack. 'A:H' (Availability: High) captures the complete denial of IPsec forwarding. The score is not higher because the vulnerability is scoped to a single device and a specific traffic class (IPsec), not a system-wide or multi-user outage.

Frequently asked questions