Broken in new Windows update... Steam + moshortcut:// + script extender loader

[wisteso]

The problem:

After Windows 11 forced the Feburary 2024 (KB5034765) cumulative update, MO2 suddenly fails to start games which use a script extender loader if you use a moshortcut:// via Steam.

Example:

This is necessary in order to use ModOrganizer2 when also playing with SteamLink Streaming, due to needing a 'one-click' route into the game for BigPicture mode.

To Reproduce:

Steps to reproduce the behavior:

1. Update to Windows 11 with KB5034765 (which put me on build 22621.3155)
2. Configure Steam to launch your game using ModOrganizer.exe with a moshortcut://
3. Make sure ModOrganizer.exe is not already running
4. Attempt to start the game in Steam
5. Observe error message every time

Environment:

• Mod Organizer Version that exhibits the issue: 2.50
• Last Mod Organizer Version that did not exhibit the issue (if applicable): 2.50
• Desktop OS/version used to run Mod Organizer: Windows 11 22H2 (build 22621.3155)

Details:

Using launch options in Steam to run ModOrganizer2.exe with an appropriate moshortcut:// had worked fine in previous windows builds.

The specific error is:

The failure happens with both Fallout4 + Fallout New Vegas, and likely any other game using a script extender loader exe.

Other notes:

• Still works if you click the 'Run' button from within MO2.
• Still works if you run the moshortcut:// via Steam while MO2 is already running.
• Still works if you double click a MO2 generated shortcut that runs the moshortcut://, even if MO2 was not running before.
• Having Windows Security exceptions for ModOrganizer doesn't seem to help.
• Issue still happens if Steam is started as an administrator.

USVFS:

It's short so I'm just going to in-line
22:30:13.364 [I] usvfs dll 0.5.5.1 initialized in process 27224
22:30:13.365 [D] remove from process 27224
22:30:13.365 [I] create config in 27224
22:30:13.365 [I] 0 processes
22:30:13.365 [I] mod_organizer_instance_1 created in process 27224
22:30:13.365 [I] attached to mod_organizer_instance_1 with 1 nodes, size 4,194,304 B
22:30:13.365 [I] inv_mod_organizer_instance_1 created in process 27224
22:30:13.365 [I] attached to inv_mod_organizer_instance_1 with 1 nodes, size 131,072 B
22:30:13.365 [D] context current shm: mod_organizer_instance (now 2 connections)
22:30:13.365 [D] clearing blacklist
22:30:13.365 [D] blacklisting 'Chrome.exe'
22:30:13.365 [D] blacklisting 'Firefox.exe'
22:30:13.365 [D] blacklisting 'TSVNCache.exe'
22:30:13.365 [D] blacklisting 'TGitCache.exe'
22:30:13.365 [D] blacklisting 'Steam.exe'
22:30:13.365 [D] blacklisting 'GameOverlayUI.exe'
22:30:13.365 [D] blacklisting 'Discord.exe'
22:30:13.365 [D] blacklisting 'GalaxyClient.exe'
22:30:13.365 [D] blacklisting 'Spotify.exe'
22:30:13.365 [D] blacklisting 'Brave.exe'
22:30:13.365 [D] clearing forced libraries
22:30:13.678 [D] clearing forced libraries
22:30:13.683 [E] failed to spawn "D:\SteamLibrary\steamapps\common\Fallout 4\f4se_loader.exe"

MO Interface:

[2024-02-19 04:30:13.657 D] refresh done
[2024-02-19 04:30:13.657 D] timing: OrganizerCore::onDirectoryRefreshed() 1 ms
[2024-02-19 04:30:13.673 D] Updating VFS mappings...
[2024-02-19 04:30:13.675 D] VFS mappings updated, linked 7 dirs and 5 files in 16ms
[2024-02-19 04:30:13.678 D] checking steam
[2024-02-19 04:30:13.678 D] managed game is located at 'D:/SteamLibrary/steamapps/common/Fallout 4' and file 'D:/SteamLibrary/steamapps/common/Fallout 4/steam_api64.dll' exists
[2024-02-19 04:30:13.683 D] 'steam.exe' is running, accessible=yes
[2024-02-19 04:30:13.683 D] spawning binary:
[2024-02-19 04:30:13.683 D]  . exe: 'D:/SteamLibrary/steamapps/common/Fallout 4/f4se_loader.exe'
[2024-02-19 04:30:13.683 D]  . args: ''
[2024-02-19 04:30:13.683 D]  . cwd: 'D:/SteamLibrary/steamapps/common/Fallout 4'
[2024-02-19 04:30:13.683 D]  . steam id: ''
[2024-02-19 04:30:13.683 D]  . hooked: true
[2024-02-19 04:30:13.683 D]  . stdout: no
[2024-02-19 04:30:13.683 D]  . stderr: no
[2024-02-19 04:30:13.683 D]  . real cmd: '"D:\SteamLibrary\steamapps\common\Fallout 4\f4se_loader.exe"'
[2024-02-19 04:30:13.685 E] Error 5 ERROR_ACCESS_DENIED: Accessisdenied. (0x5)
[2024-02-19 04:30:13.685 E]  . binary: 'D:\SteamLibrary\steamapps\common\Fallout 4\f4se_loader.exe'
[2024-02-19 04:30:13.685 E]  . owner: (this user)
[2024-02-19 04:30:13.685 E]  . rights: (normal rights)
[2024-02-19 04:30:13.685 E]  . arguments: ''
[2024-02-19 04:30:13.685 E]  . cwd: 'D:\SteamLibrary\steamapps\common\Fallout 4'
[2024-02-19 04:30:13.685 E]  . stdout: no, stderr: no, hooked: yes
[2024-02-19 04:30:13.685 E]  . MO elevated: no
[2024-02-19 04:30:13.685 E]  . usvfs x86:ok x64:ok proxy_x86:ok proxy_x64:ok