CVE-2026-73439 in EOS
Summary
by MITRE • 09/16/2026
On affected platforms running Arista EOS, if OpenConfig is configured and running a gNMI server on the system, and if gNSI Pathz is configured and a gNSI Pathz policy is present on the system, then gNMI may fail to correctly enforce the rules in this policy if both a group rule and a user rule for the same path is present in the policy. Under certain conditions, this can lead to an authenticated user gaining unauthorized permission to read or write gNMI paths that the Pathz policy is intended to restrict.
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Analysis
by VulDB Data Team • 09/16/2026
The vulnerability described involves a critical authorization bypass within Arista EOS when OpenConfig and gNSI Pathz are configured alongside a running gNMI server. This flaw specifically manifests in scenarios where both group-level rules and user-specific rules target the same network path within a single policy configuration. The underlying technical failure lies in the logic used to enforce access control lists, which fails to correctly prioritize or merge these overlapping permissions. Instead of applying the most restrictive rule as intended by security best practices, the system may erroneously grant access based on one of the conflicting rules, effectively creating an authorization gap that allows authenticated users to bypass restrictions designed to limit their scope of operation.
From a technical perspective, this issue represents a classic case of improper privilege assignment or broken access control logic within the network management interface layer. When gNMI attempts to validate a request against the configured Pathz policy, it encounters ambiguity in how group and user rules are evaluated for identical paths. This lack of deterministic enforcement means that an attacker with valid credentials can exploit this inconsistency to read sensitive configuration data or write unauthorized changes to device settings. The vulnerability is particularly dangerous because gNMI serves as a primary interface for automated network management tools, meaning that compromising these permissions could allow an adversary to manipulate the entire network infrastructure without detection by standard monitoring systems that rely on explicit policy violations rather than logic flaws.
The operational impact of this vulnerability is severe, potentially leading to unauthorized data exfiltration or malicious configuration changes across the affected Arista switches and routers. An authenticated attacker with limited privileges could escalate their access level simply by leveraging the conflict between group and user rules. This could result in the disclosure of network topology details, credential theft if such information is exposed through gNMI paths, or even denial of service conditions if critical routing protocols are disrupted via unauthorized write operations. The presence of this flaw undermines the integrity of zero-trust architectures that rely on granular access controls enforced by tools like Pathz to segment administrative duties and limit lateral movement within a data center environment.
This vulnerability aligns with CWE-269, which covers Improper Privilege Assignment, as well as CWE-862, Missing Authorization Check, depending on the specific configuration state that triggers the bypass. In terms of the MITRE ATT&CK framework for enterprise networks, this flaw facilitates techniques related to Collection and Exfiltration over Network Service or Command and Control via Application Layer Protocol if an attacker uses gNMI to maintain persistence or exfiltrate data. It also relates to Defense Evasion by allowing attackers to operate within what appears to be a permitted scope while actually violating the intended policy boundaries.
Mitigation strategies should focus on immediate remediation of the configuration logic that triggers this conflict. Administrators must review all active gNSI Pathz policies and ensure that there are no overlapping group and user rules targeting the same paths, as removing one layer of these conflicting permissions resolves the ambiguity in enforcement. If such overlaps are unavoidable due to complex organizational requirements, it is crucial to verify which rule takes precedence and test thoroughly before deployment. Additionally, keeping Arista EOS updated with the latest software releases provided by the vendor is essential, as patches for this issue will likely address the underlying code logic responsible for the incorrect policy evaluation. Network security teams should also implement strict monitoring on gNMI traffic to detect any anomalous access patterns that might indicate exploitation of this flaw before a patch can be applied.