[SECURITY] - An attacker can write files with exact names to arbitrary locations on the filesystem #714

Description

Xreader 4.6.3 (commit ef5a50d) passes the raw PDF attachment filename directly to g_file_get_child() when saving attachments via "Save Attachment As...". Since g_file_get_child() resolves ../ sequences, an attacker-controlled filename can escape the user-selected target directory and write files to arbitrary locations with the exact filename specified by the attacker — no random suffix.

This is the most critical of the attachment vulnerabilities, as it enables writing .desktop files (or any other file) with precise names to arbitrary locations, leading to arbitrary code execution.

Affected Code

shell/ev-window.c:7374:

save_to = g_file_get_child(target_file, ev_attachment_get_name(attachment));

shell/ev-window.c:7400:

dest_file = g_file_get_child(target_file, ev_attachment_get_name(attachment));

Both the local and remote save paths use the unsanitized attachment name.

Steps to Reproduce

1. Generate a malicious PDF using the PoC script from the full report — the attachment is named ../Desktop/test.desktop and contains a valid .desktop entry that executes an arbitrary command
2. Open poc.pdf in xreader
3. In the sidebar, right-click the attachment and select "Save Attachment As..."
4. Select any directory (e.g., ~/Documents/)
5. test.desktop is written to ~/Desktop/ instead of the selected directory
6. Double-clicking the .desktop file executes the embedded command

Suggested Fix

Extract the basename before passing to g_file_get_child() in both code paths:

// line 7374
-save_to = g_file_get_child(target_file, ev_attachment_get_name(attachment));
+gchar *basename = g_path_get_basename(ev_attachment_get_name(attachment));
+save_to = g_file_get_child(target_file, basename);
+g_free(basename);

// line 7400
-dest_file = g_file_get_child(target_file, ev_attachment_get_name(attachment));
+gchar *basename = g_path_get_basename(ev_attachment_get_name(attachment));
+dest_file = g_file_get_child(target_file, basename);
+g_free(basename);

Impact

An attacker can write files with exact names to arbitrary locations on the filesystem. By writing a .desktop file to ~/Desktop/, arbitrary code execution is achieved when the user double-clicks it. The only user interaction required is opening the PDF, right-clicking the attachment, selecting "Save As", and choosing any directory.

References

• Full vulnerability report with PoC scripts and video demonstrations