CVE-2026-53769 in Avo
Summary
by MITRE • 09/05/2026
Avo is a framework to create admin panels for Ruby on Rails apps. From version 2.28.0 to before version 3.32.0, Avo's direct attachment upload endpoint lacks server-side upload authorization and bypasses the documented field-level upload policy methods such as upload_{FIELD_ID}?. An authenticated Avo user who can reach the Avo attachment upload endpoint can replace or add attachment content, including binary content, filename, and content-type metadata, on a resolved record even when both update? and upload_<field>? policies deny the operation. This primarily affects multi-role Avo Pro/Advanced-style deployments where non-administrator or restricted operator users can reach Avo and per-record or per-field operations are expected to be enforced by policies. This issue has been patched in version 3.32.0.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 09/06/2026
The vulnerability identified within the Avo framework for Ruby on Rails applications represents a critical failure in server-side access control mechanisms, specifically affecting versions from 2.28.0 up to but not including 3.32.0. This security flaw centers on the direct attachment upload endpoint, which fails to enforce proper authorization checks before processing file uploads. In secure application design, particularly within frameworks that support role-based or policy-driven access control like Avo Pro and Advanced editions, it is imperative that all data manipulation operations are validated against defined policies at the server level. The absence of such validation allows authenticated users who have basic access to the Avo interface to bypass granular field-level restrictions intended by administrators. This discrepancy between documented policy methods, such as upload_{FIELD_ID}?, and actual runtime enforcement creates a significant gap in security posture that can be exploited by malicious actors or compromised accounts within multi-role deployments where strict separation of duties is expected.
Technically, the flaw manifests when an authenticated user interacts with the attachment upload endpoint to replace or add content to a resolved record. Despite explicit policy configurations denying update permissions and specific field-level upload restrictions via methods like upload_<field>?, the server processes these requests without verifying whether the current user possesses the requisite privileges for that specific action. This allows attackers to inject arbitrary binary content, manipulate filename metadata, and alter content-type headers associated with existing records. The ability to overwrite or append files bypasses intended business logic constraints designed to protect sensitive data fields or restrict certain users from modifying critical assets. Such behavior aligns closely with CWE-284 Improper Access Control, as the application fails to properly control access to a protected object based on user roles and permissions. Furthermore, this exploitation vector is consistent with MITRE ATT&CK technique T1078 Valid Accounts, where an attacker leverages legitimate credentials to perform unauthorized actions that should be restricted by administrative policies.
The operational impact of this vulnerability is severe in environments utilizing multi-role configurations typical of Avo Pro or Advanced deployments. In these scenarios, non-administrator users or restricted operators are granted limited access to specific parts of the application under the assumption that field-level and record-level policies will enforce their boundaries. The bypass allows these users to escalate their effective privileges by modifying data they should not be able to touch, potentially leading to data integrity issues, information disclosure through uploaded malicious files, or even remote code execution if the uploaded content is processed in a vulnerable manner elsewhere in the application stack. For instance, uploading executable scripts disguised as benign file types could lead to server-side compromises if subsequent processing steps do not sanitize inputs thoroughly. The lack of enforcement undermines trust in the framework’s security model and exposes organizations to risks associated with unauthorized data modification and potential compliance violations regarding data integrity controls.
Mitigation strategies must prioritize immediate upgrading to version 3.32.0 or later, where this authorization bypass has been patched by implementing robust server-side checks that respect both global update policies and specific field-level upload restrictions. Until an upgrade is feasible, administrators should consider restricting direct access to the attachment endpoints through network-level controls such as firewall rules or reverse proxy configurations if those users do not require file upload capabilities. Additionally, reviewing and tightening policy definitions across all models can help ensure that any future vulnerabilities are less exploitable by enforcing stricter validation logic at multiple layers of the application architecture. Regular security audits focusing on access control implementations in Ruby on Rails applications are recommended to detect similar misconfigurations where client-side or framework-default behaviors do not align with intended security policies.