CVE-2026-93676 in Red Hat
Summary
by MITRE • 09/18/2026
xdg-dbus-proxy incorrectly filters D-Bus broadcast messages, bypassing configured path, interface, and member restrictions. This allows a sandboxed Flatpak application to intercept broadcast signals on the D-Bus session bus and AT-SPI bus that should be restricted, potentially exposing sensitive information to unauthorized applications.
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Analysis
by VulDB Data Team • 09/18/2026
The vulnerability in xdg-dbus-proxy represents a critical failure in access control logic within the mechanism designed to mediate communication between sandboxed Flatpak applications and system services via D-Bus. As a cyber security specialist with extensive experience in containerization and inter-process communication, it is evident that this flaw undermines the fundamental isolation guarantees provided by modern desktop environments. The xdg-dbus-proxy serves as an intermediary, enforcing policies defined by application manifests to restrict which D-Bus paths, interfaces, and members are accessible to untrusted software. However, the implementation contains a logical error where broadcast messages, specifically signals sent without a specific destination object path or intended for all listeners on the bus, bypass these configured restrictions entirely. This oversight allows any sandboxed process utilizing this proxy to subscribe to and intercept high-level system events that were explicitly denied in its security policy.
From a technical perspective, D-Bus operates with two primary types of messages: method calls and signals. Method calls are directed at specific object paths and interfaces, requiring explicit permission for the caller to interact with them. Signals, particularly broadcast or wildcarded signals, are emitted by services to notify all interested parties about state changes without targeting a single recipient. The vulnerability arises because the filtering logic within xdg-dbus-proxy fails to apply path, interface, and member constraints when processing these broadcast messages. Consequently, an attacker controlling a malicious Flatpak application can exploit this gap to listen to signals that should remain invisible to it. This is not merely a theoretical risk but a practical avenue for information disclosure, as many system services emit detailed state changes through the session bus and the AT-SPI accessibility bus.
The operational impact of this vulnerability is significant, primarily centering on unauthorized data exposure and potential privilege escalation vectors within the user space. By intercepting broadcast signals from the D-Bus session bus, a compromised application can gather sensitive information about other running applications, such as window titles, active desktop environments, or specific service states that indicate user activity patterns. Furthermore, access to AT-SPI broadcasts is particularly dangerous because these messages often contain accessibility-related data, including text content of UI elements and focus changes. An attacker could leverage this capability to perform keystroke logging indirectly by monitoring which application currently has input focus or extracting sensitive text displayed in accessible interfaces. This effectively breaks the sandbox boundary, allowing a low-privilege process to gain insights into high-privilege contexts without requiring elevated system permissions directly.
This flaw aligns with CWE-200, Information Exposure, as it allows an unauthorized actor to access information that is not intended for them due to improper filtering controls. Additionally, the exploitation technique relates to ATT&CK tactic T1537, Communication Through Removable Media or Backup System, in a broader sense of lateral movement and data exfiltration within the host environment, though more specifically it fits under T1046, Network Service Discovery, as the attacker maps out active services and their states. The lack of proper validation for broadcast message routing constitutes an access control bypass that compromises the integrity of the security model provided by Flatpak.
Mitigation strategies must focus on immediate patching and rigorous policy verification. Users should update xdg-dbus-proxy to a version where this filtering logic has been corrected to enforce restrictions consistently across all D-Bus message types, including broadcasts. Developers relying on Flatpak for application distribution must ensure their build pipelines include the latest security patches for base runtime components. Furthermore, system administrators and developers should review existing flatpak applications that require broad access permissions; if an application does not legitimately need to receive broadcast signals from specific services, its manifest should be tightened to explicitly deny those paths rather than relying on default behaviors which may have been incorrectly implemented in the proxy layer. Continuous monitoring of D-Bus traffic for anomalous subscription patterns can also help detect exploitation attempts in real-time while patches are being deployed across affected systems.