Windows Security / Application Control blocks both ark.exe and R package cli.dll

[davidjanmassgov]

Windows Security / Application Control blocks both ark.exe and R package cli.dll

I am seeing Windows Security block components after reinstalling Positron on a new computer. This has happened on this new work computer and my personal computer. I am up to date on all my Windows updates.

I found Issue #6226, which reports security software flagging ark.exe. My issue appears similar, but the alerts are from Windows Security / Application Control rather than Trend Micro.

What Windows Security is blocking

Windows Security displayed a notification that part of the R for Windows terminal front-end was blocked because it could not confirm the publisher of cli.dll.

I also received a separate Windows Security notification for Positron's R kernel executable:

C:\Users\David.Jan\AppData\Local\Programs\Positron\resources\app\extensions\positron-r\resources\ark\windows-x64\ark.exe

Result in Positron

After the cli.dll block, R cannot load tibble or tidyverse:

Error:
! package or namespace load failed for ‘tidyverse’:
.onAttach failed in attachNamespace() for 'tidyverse', details:
call: NULL
error: package or namespace load failed for ‘tibble’ in inDL(x, as.logical(local), as.logical(now), ...):
unable to load shared object 'C:/Users/David.Jan/AppData/Local/Programs/R/R-4.6.1/library/cli/libs/x64/cli.dll':
LoadLibrary failure: An Application Control policy has blocked this file.

R package DLL blocked:
C:\Users\David.Jan\AppData\Local\Programs\R\R-4.6.1\library\cli\libs\x64\cli.dll

Positron executable flagged:
C:\Users\David.Jan\AppData\Local\Programs\Positron\resources\app\extensions\positron-r\resources\ark\windows-x64\ark.exe

Positron Version: 2026.10.0 (user setup) build 297
Code - OSS Version: 1.134.0
Commit: 73a7e19
Date: 2026-10-08T16:46:29+02:00
Electron: 42.8.1
Chromium: 148.0.7778.280
Node.js: 24.18.1
V8: 14.8.178.38-electron.0
OS: Windows_NT x64 10.0.26200

[juliasilge]

Thanks for the detailed report! Those two notifications come from Smart App Control, a Windows 11 code-integrity feature that is separate from Microsoft Defender's antivirus scanning. You can confirm it is active by running this in PowerShell:

Get-MpComputerStatus | Select-Object SmartAppControlState

or by checking Settings > Privacy & security > Windows Security > App & browser control > Smart App Control settings.

This is a different situation from the antivirus false positives we have seen before (for example #6226), and a couple of details in your report point to what is really going on.

What is actually being blocked

Neither notification says Rterm or ark.exe were blocked from running. Both say Windows "can't confirm who published" a DLL the app tried to load, and in the first one that file is cli.dll. That matches your Positron error: the R console started fine, then failed at LoadLibrary for C:/Users/David.Jan/AppData/Local/Programs/R/R-4.6.1/library/cli/libs/x64/cli.dll.

cli.dll belongs to the cli package installed from CRAN into your R package library. CRAN's package binaries are not Authenticode-signed, not by Posit and not by CRAN. Smart App Control requires a verifiable publisher, so it will block most compiled R packages (cli, rlang, vctrs, and friends), which is what breaks tibble and tidyverse.

Two consequences of that:

• I don't think this one is actually Positron-specific. I'm pretty sure any tool running this R installation will hit the same wall. As a sanity check, try library(tibble) in Rgui on your new computer; I would expect you would see the same failure there.
• There is nothing within Positron we can sign or verify or change to fix it, since the blocked file isn't ours. For the record, we do Authenticode-sign every Windows binary we ship, such as Positron.exe, the installers, and ark.exe (see Windows: Provide code signatures on all Posit-built binaries #9962), which is why those run and only the unsigned CRAN DLL gets blocked.

What you can do

I'm not an expert on this, but my research indicates that Smart App Control unfortunately has no allowlist or per-file unblock mechanism so your options are limited. I think I would recommend that you check with IT, since Smart App Control can be enforced by organizational policy. If it turns out your work machine is actually enforcing a WDAC/App Control for Business policy rather than Smart App Control (visible in Event Viewer under Applications and Services Logs > Microsoft > Windows > CodeIntegrity > Operational), then actually it is entirely IT-managed and they would need to add allow rules for R and its package library.

We would also encourage you to report this to Microsoft via the Feedback Hub. Smart App Control is supposed to avoid interfering with well-behaved software, and R with CRAN packages is a super regular/mainstream workflow.