CVE-2026-55888

A flaw was found in xdg-desktop-portal. An attacker operating a sandboxed application can bypass isolation boundaries to gain unauthorized access to host files. This issue occurs because the FileChooser interface fails to properly validate filenames before passing them to backend services. Consequently, a malicious application can create and manipulate arbitrary files on the host system, limited only by the permissions of the current user.

This vulnerability is rated as Important because a rogue or compromised sandboxed client can escape its confinement boundaries and compromise the integrity of host files under the active user account. On Red Hat Enterprise Linux systems running graphical desktop environments with containerized desktop applications, the xdg-desktop-portal service mediates filesystem operations between isolated applications and the host. Insufficient path verification during file export operations enables untrusted sandboxed payloads to write outside designated container boundaries, although exploitation requires an active local user session and cannot grant privileges beyond those of the executing user.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.

--- CME Mitigation Guidance (2026-11-02) --- Disclaimer: The following mitigation solutions are provided as a courtesy, pending the application of an official patch. This content was generated utilizing AI tools in conjunction with data from https://cmetaxonomy.org. Customers are advised to independently evaluate and test these temporary mitigations within their own infrastructure.

The highest-value action is to enforce strict filename canonicalization and validation on FileChooser.SaveFiles inputs to prevent directory traversal across backend directory concatenation: upgrade to xdg-desktop-portal 1.22.1 (or the fixed Xdg Desktop Portal builds), which validate filenames provided in the files option of FileChooser.SaveFiles to ensure they do not traverse directories, closing all 2 injection vectors (crafted filenames via FileChooser.SaveFiles 'files' option, path traversal during directory concatenation in portal backend). Until patched, this is only a concern on Linux desktop environments running sandboxed applications with D-Bus access to xdg-desktop-portal — non-Linux deployments and headless server environments without graphical desktop portals are unaffected — so restrict untrusted sandboxed applications from communicating with the portal D-Bus interface and exercise caution when interacting with file saving prompts. As a compensating measure, audit filesystem system calls using auditd to log and alert on unexpected file creation outside sandboxed application directories, restrict backend filesystem writes strictly to the explicitly selected directory to block traversal outside chosen folder boundaries, run SELinux in enforcing mode to restrict unauthorized file creation across host domains, apply Landlock filesystem sandboxing to restrict portal service write boundaries across host directories, deploy EDR agents to detect anomalous host file creation and path traversal behavior initiated via the portal service, and implement Falco or eBPF runtime security probes to detect anomalous host file write operations initiated by portal backend processes. These controls limit blast radius and contain exploitation, but they do not fix the underlying unvalidated-filename path traversal defect — apply the upstream patch to fully remediate.

Highest-impact CME: CME-1301 Path Traversal Prevention (Canonicalization) (high)