diff --git a/eng/Signing.props b/eng/Signing.props
index c3fd63545484ff..56a3574f0abda2 100644
--- a/eng/Signing.props
+++ b/eng/Signing.props
@@ -49,9 +49,13 @@
     <MacOSPkg Include="$(ArtifactsPackagesDir)**/dotnet-runtime*.pkg" Exclude="$(ArtifactsPackagesDir)**/dotnet-runtime-internal*.pkg" />
     <FileSignInfo Include="@(MacOSPkg->'%(Filename)%(Extension)')" CertificateName="MacDeveloperWithNotarization" />
 
-    <!-- We don't need to code sign .js files because they are not used in Windows Script Host. -->
-    <!-- WARNING: Needs to happed outside of any target -->
+    <!-- JS files are customer-modifiable runtime/toolchain files. They cannot be
+         Authenticode-signed because modifying a signed file breaks the signature.
+         Instead, a catalog file (.cat) is generated and signed to provide integrity
+         verification. See the GenerateCatalogFiles target in eng/mono.proj. -->
     <FileExtensionSignInfo Update=".js" CertificateName="None" />
+    <FileExtensionSignInfo Include=".cab" CertificateName="Microsoft400" />
+    <FileExtensionSignInfo Include=".cat" CertificateName="Microsoft400" />
 
     <!-- Third-party components which should be signed.  -->
     <FileSignInfo Include="Antlr4.Runtime.Standard.dll" CertificateName="3PartySHA2" />
diff --git a/eng/generate-catalog.ps1 b/eng/generate-catalog.ps1
new file mode 100644
index 00000000000000..4f8626c5205c4b
--- /dev/null
+++ b/eng/generate-catalog.ps1
@@ -0,0 +1,93 @@
+<#
+.SYNOPSIS
+    Generates a catalog definition file (.cdf) and catalog file (.cat) for all .js files
+    in the specified root directory. Used for VS signing compliance - the .js files are
+    customer-modifiable and cannot be directly Authenticode-signed.
+
+.PARAMETER RootPath
+    Root directory to search for .js files recursively.
+
+.PARAMETER CatOutputPath
+    Full path for the output .cat file.
+#>
+param(
+    [Parameter(Mandatory)][string]$RootPath,
+    [Parameter(Mandatory)][string]$CatOutputPath,
+    [string]$WindowsSdkDir = '',
+    [switch]$ErrorIfMakecatNotFound
+)
+
+$ErrorActionPreference = 'Stop'
+
+$cdfPath = [System.IO.Path]::ChangeExtension($CatOutputPath, '.cdf')
+
+$files = Get-ChildItem -Path $RootPath -Recurse -Filter '*.js' -File
+if ($files.Count -eq 0) {
+    Write-Warning "No .js files found under $RootPath - skipping catalog generation."
+    exit 0
+}
+
+$cdf = @()
+$cdf += '[CatalogHeader]'
+$cdf += "Name=$CatOutputPath"
+$cdf += 'CatalogVersion=2'
+$cdf += 'HashAlgorithms=SHA256'
+$cdf += ''
+$cdf += '[CatalogFiles]'
+
+$i = 0
+foreach ($f in $files) {
+    $label = "js_${i}_" + ($f.Name -replace '[^\w\.-]', '_')
+    $cdf += "<hash>$label=$($f.FullName)"
+    $i++
+}
+
+$cdf | Set-Content -Path $cdfPath -Encoding ASCII
+Write-Host "Generated CDF with $($files.Count) .js files at $cdfPath"
+
+$catDir = [System.IO.Path]::GetDirectoryName($CatOutputPath)
+if (-not (Test-Path $catDir)) {
+    New-Item -ItemType Directory -Path $catDir -Force | Out-Null
+}
+
+# Find makecat.exe - it ships with the Windows SDK and may not be on PATH.
+$makecat = $null
+if ($WindowsSdkDir -and (Test-Path $WindowsSdkDir)) {
+    $makecat = Get-ChildItem -Path (Join-Path $WindowsSdkDir 'bin') -Recurse -Filter 'makecat.exe' -File |
+        Where-Object { $_.DirectoryName -match 'x64' } |
+        Sort-Object DirectoryName -Descending |
+        Select-Object -First 1
+}
+
+if (-not $makecat) {
+    $makecat = Get-Command makecat.exe -ErrorAction SilentlyContinue
+}
+
+if (-not $makecat) {
+    # Fallback: search common Windows SDK locations
+    $sdkRoot = "${env:ProgramFiles(x86)}\Windows Kits\10\bin"
+    if (Test-Path $sdkRoot) {
+        $makecat = Get-ChildItem -Path $sdkRoot -Recurse -Filter 'makecat.exe' -File |
+            Where-Object { $_.DirectoryName -match 'x64' } |
+            Sort-Object DirectoryName -Descending |
+            Select-Object -First 1
+    }
+}
+
+if (-not $makecat) {
+    if ($ErrorIfMakecatNotFound) {
+        throw "makecat.exe not found. Catalog signing requires the Windows SDK which must be available in CI builds."
+    }
+    Write-Warning "makecat.exe not found - skipping catalog generation. Catalog signing requires the Windows SDK."
+    exit 0
+}
+
+$makecatPath = if ($makecat -is [System.Management.Automation.CommandInfo]) { $makecat.Source } else { $makecat.FullName }
+Write-Host "Using makecat.exe at: $makecatPath"
+
+& $makecatPath $cdfPath
+if ($LASTEXITCODE -ne 0) {
+    throw "makecat.exe failed with exit code $LASTEXITCODE"
+}
+
+Write-Host "Generated catalog file: $CatOutputPath"
diff --git a/src/installer/pkg/sfx/Microsoft.NETCore.App/Microsoft.NETCore.App.Runtime.Mono.sfxproj b/src/installer/pkg/sfx/Microsoft.NETCore.App/Microsoft.NETCore.App.Runtime.Mono.sfxproj
index f074aa4c2e5e06..1124e28af09246 100644
--- a/src/installer/pkg/sfx/Microsoft.NETCore.App/Microsoft.NETCore.App.Runtime.Mono.sfxproj
+++ b/src/installer/pkg/sfx/Microsoft.NETCore.App/Microsoft.NETCore.App.Runtime.Mono.sfxproj
@@ -70,4 +70,29 @@
       <ReferenceCopyLocalPaths Include="@(MonoRuntimeFiles)" />
     </ItemGroup>
   </Target>
+
+  <!--
+    Generate a catalog (.cat) file covering all .js files in the runtime pack.
+    The .js files are customer-modifiable runtime/toolchain files that cannot be
+    directly Authenticode-signed. The .cat provides integrity verification without
+    preventing modification. Only runs on Windows (makecat.exe is a Windows SDK tool)
+    and only for browser-wasm packs which contain .js files.
+  -->
+  <Target Name="GenerateCatalogFiles" AfterTargets="AddMonoRuntimeFiles"
+          Condition="$([MSBuild]::IsOSPlatform('Windows')) and '$(RuntimeIdentifier)' == 'browser-wasm'">
+    <PropertyGroup>
+      <_CatOutputPath>$(ArtifactsObjDir)mono-pack\mono-runtime-js.cat</_CatOutputPath>
+      <_ErrorIfMakecatNotFound Condition="'$(ContinuousIntegrationBuild)' == 'true' or '$(OfficialBuild)' == 'true'">-ErrorIfMakecatNotFound</_ErrorIfMakecatNotFound>
+    </PropertyGroup>
+
+    <Exec Command="powershell.exe -NoProfile -ExecutionPolicy Bypass -Command &quot;&amp; '$(RepoRoot)eng\generate-catalog.ps1' -RootPath '$(MonoObjDir)' -CatOutputPath '$(_CatOutputPath)' -WindowsSdkDir '$(WindowsSdkDir)' $(_ErrorIfMakecatNotFound)&quot;" StandardOutputImportance="High" />
+
+    <ItemGroup Condition="Exists('$(_CatOutputPath)')">
+      <ReferenceCopyLocalPaths Include="$(_CatOutputPath)">
+        <TargetPath>runtimes/$(RuntimeIdentifier)/native/mono-runtime-js.cat</TargetPath>
+        <ExcludeFromDataFiles>true</ExcludeFromDataFiles>
+      </ReferenceCopyLocalPaths>
+    </ItemGroup>
+    <Message Condition="Exists('$(_CatOutputPath)')" Importance="High" Text="Generated catalog file: $(_CatOutputPath)" />
+  </Target>
 </Project>