CVE-2026-110039 in Smush Plugin
Summary
by MITRE • 10/16/2026
The Smush WordPress plugin before 4.3.4 does not restrict changes to a network-wide access setting to network administrators, allowing an administrator of a single site on a multisite network to change it for the entire network.
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Analysis
by VulDB Data Team • 10/16/2026
The vulnerability identified in versions of the Smush image optimization plugin prior to version 4.3.4 represents a critical failure in role-based access control within WordPress multisite environments. This flaw specifically targets the administrative interface where configuration settings are managed, exposing a significant gap in privilege separation that undermines the security model intended for multi-tenant deployments. In standard WordPress architectures, permissions are strictly tiered to ensure that users with limited privileges cannot alter system-wide configurations or affect other sites within the same installation. However, this specific implementation error allows an administrator assigned to only one site on a multisite network to modify settings that are designated as global and intended exclusively for super administrators.
The technical root cause lies in insufficient capability checks during the processing of administrative requests related to Smush's network-wide access controls. When a user submits changes to these settings, the plugin fails to verify whether the requesting user possesses the necessary elevated privileges required for such operations. Instead, it accepts and processes the request based on lower-level permissions that are typically granted to individual site administrators. This lack of validation means that any authenticated user with the ability to edit their specific site's configuration can inadvertently or maliciously alter settings that apply across the entire network infrastructure. The absence of a proper capability check for super-administrator status is the direct enabler of this unauthorized state change.
The operational impact of this vulnerability extends beyond simple privilege escalation, affecting data integrity and system stability across all sites hosted on the affected WordPress installation. By allowing lower-privileged administrators to modify global settings, attackers or compromised accounts can disrupt image optimization processes for every site in the network simultaneously. This could lead to degraded performance if optimal compression levels are disabled, increased bandwidth costs due to uncompressed images being served, or potential exposure of sensitive metadata embedded within images that would otherwise be stripped by security-focused configurations. Furthermore, this flaw facilitates lateral movement within a compromised environment, as an attacker gaining access to a low-privilege site can leverage it to manipulate the broader infrastructure without needing higher-level credentials.
This vulnerability aligns with CWE-269, which describes Improper Privilege Management, specifically highlighting scenarios where users are granted excessive privileges or can perform actions outside their intended scope. From a tactical perspective, this behavior is consistent with ATT&CK technique T1078, Valid Accounts, as it allows an attacker to use legitimate but insufficiently privileged credentials to achieve broader system control. It also touches upon CWE-284, Improper Access Control, by demonstrating how the application fails to enforce separation of duties between different administrative roles within a multisite architecture.
Mitigation strategies must prioritize immediate updates and rigorous access control auditing. The most effective remediation is upgrading the Smush plugin to version 4.3.4 or later, where these permission checks have been corrected to properly restrict network-wide setting modifications to super administrators only. In environments where updating may not be immediately feasible, temporary mitigations include restricting administrative capabilities for individual site admins through custom role definitions and monitoring admin activity logs for unauthorized changes to global plugin settings. Additionally, implementing strict input validation on the server side to verify user roles before processing configuration updates can provide a defense-in-depth layer against similar privilege escalation attempts in other plugins or core functionalities.