CVE-2026-46529: PDF /GoToR action argv injection enables single-click RCE via --gtk-module dlopen

Atril Document Viewer is the default document reader of the MATE desktop environment for Linux. A single-click remote code execution vulnerability in versions prior to 1.26.3 and 1.28.4 allows an attacker to achieve arbitrary code execution as the user by tricking them into clicking a link inside a malicious PDF document. The PDF can be packaged as a polyglot file that is simultaneously a valid PDF and a valid ELF shared library, making the attack a single-file, single-click, configuration-independent RCE on stock atril installations. The root cause is shell/ev-application.c:evspawn, which builds a command line from attacker-controlled PDF link-destination fields without applying gshellquote. The cmdline is then handed to gappinfocreatefromcommandline, which shell-parses it back into argv — splitting any embedded --gtk-module=PATH into a separate argv element. GTK then dlopen()s the path during init, running any attribute((constructor)) it finds. Versions 1.26.3 and 1.28.4 contain a patch for the issue. This is the same defect class as CVE-2023-51698 (CBT --checkpoint-action injection in comics-document.c, fixed in 1.6.2) but in a different code path (shell/ev-application.c) that the original patch did not touch.