Protect elevated working folder from malicious data

When running elevated, Burn uses the Windows Temp folder as its working folder
to prevent normal processes from tampering with the files. Windows Temp does
allow non-elevated processes to write to the folder but they cannot see the
files there. Unfortunately, contrary to our belief, non-elevated processes
can read the files in Windows Temp by watching for directory changes. This
allows a malicious process to lie in wait, watching the Windows Temp folder
until a Burn process is launched elevated, then attack the working folder.
Mitigate that attack by protecting the working folder to only elevated users.

Managed custom actions also fall back to using the Windows Temp folder in
some cases and thus can be exposed in a similar fashion as an elevated Burn
process. Remove that possibility.

1 files changed, 2 insertions, 1 deletions

diff --git a/src/burn/engine/bootstrapperapplication.cpp b/src/burn/engine/bootstrapperapplication.cpp
index 402f7015..947b3720 100644
--- a/src/burn/engine/bootstrapperapplication.cpp
+++ b/src/burn/engine/bootstrapperapplication.cpp
@@ -276,6 +276,7 @@ EXTERN_C HRESULT BootstrapperApplicationInterpretExecuteResult(
 }
 
 EXTERN_C HRESULT BootstrapperApplicationEnsureWorkingFolder(
+    __in BOOL fElevated,
     __in BURN_CACHE* pCache,
     __deref_out_z LPWSTR* psczUserExperienceWorkingFolder
     )
@@ -283,7 +284,7 @@ EXTERN_C HRESULT BootstrapperApplicationEnsureWorkingFolder(
     HRESULT hr = S_OK;
     LPWSTR sczWorkingFolder = NULL;
 
-    hr = CacheEnsureBaseWorkingFolder(pCache, &sczWorkingFolder);
+    hr = CacheEnsureBaseWorkingFolder(fElevated, pCache, &sczWorkingFolder);
     ExitOnFailure(hr, "Failed to create working folder.");
 
     hr = StrAllocFormatted(psczUserExperienceWorkingFolder, L"%ls%ls\\", sczWorkingFolder, L".ba");