CVE-2026-109119 in Rdiffweb
Summary
by MITRE • 10/16/2026
Improper Privilege Management in the user management API endpoint (/api/users/{username_or_id}) in Rdiffweb allows authenticated users to elevate their privileges to administrator by modifying the role parameter in a POST request.
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Analysis
by VulDB Data Team • 10/16/2026
The vulnerability identified as Improper Privilege Management within the RdiffWeb application represents a critical security flaw located specifically in the user management API endpoint, designated as /api/users/{username_or_id}. This issue stems from an insufficient authorization check during the processing of HTTP POST requests that modify user attributes. In a properly secured system, any operation that alters sensitive account properties, such as role assignments or administrative privileges, must be strictly gated by robust access control mechanisms that verify whether the authenticated caller possesses the requisite authority to perform the action on behalf of another user. However, in this instance, the application fails to validate if the requesting user holds administrator-level permissions before accepting and applying changes to the target account's configuration. This oversight allows any validly authenticated user, regardless of their current privilege level, to interact with this endpoint and manipulate the role parameter associated with other accounts within the system.
From a technical perspective, the flaw lies in the server-side logic that processes incoming requests to update user profiles. When an attacker sends a POST request to the specified API path, they can include a JSON or form-encoded payload containing a modified role field, typically changing it from a standard user designation to administrator. Because the backend does not enforce Role-Based Access Control (RBAC) constraints on this specific operation, the system blindly accepts and commits these changes to its database or session store. This constitutes a classic case of Insecure Direct Object Reference combined with Broken Access Control, where the application trusts client-supplied data regarding privilege levels without verifying the requester's entitlements. The vulnerability is particularly dangerous because it does not require any complex exploitation techniques; it relies solely on standard API interaction capabilities that are available to all authenticated users.
The operational impact of this vulnerability is severe and potentially catastrophic for organizations relying on RdiffWeb for secure file synchronization and backup management. By elevating their privileges to administrator, an attacker gains full control over the application environment. This includes the ability to create new administrative accounts, delete existing user data, modify system configurations, and access sensitive files stored within the repository structure. Furthermore, depending on how the underlying server is configured, high-level API endpoints often have broader implications that could extend beyond the web interface itself. An attacker with administrator privileges might be able to execute arbitrary commands if other vulnerabilities exist in conjunction with this privilege escalation, or they can exfiltrate large volumes of confidential data without restriction. This effectively compromises the confidentiality, integrity, and availability of the entire system managed by RdiffWeb.
This vulnerability aligns directly with Common Weakness Enumeration (CWE) identifiers such as CWE-269: Improper Privilege Management and CWE-862: Missing Authorization. In terms of offensive security frameworks, it maps to MITRE ATT&CK technique T1078: Valid Accounts, specifically the sub-technique for privilege escalation within a local or remote system context. The attacker leverages valid credentials to gain initial access and then exploits this logic flaw to escalate privileges, thereby achieving persistence and broader control over the target infrastructure.
To mitigate this risk, immediate action is required on the part of RdiffWeb developers and administrators. Developers must implement strict server-side authorization checks for all API endpoints that modify user roles or administrative settings. Specifically, any request attempting to change a role parameter should be intercepted by an access control middleware that verifies the requester's current privileges against a whitelist allowing only existing administrators to perform such actions. Additionally, implementing principle of least privilege across the application architecture ensures that even if one component is compromised, the blast radius remains limited. Administrators running affected versions should immediately update to patched releases where this logic has been corrected and review audit logs for any signs of unauthorized role modifications prior to patching. Regular security assessments and code reviews focusing on access control lists are also recommended to prevent similar flaws in future development cycles.