diff --git a/src/coreclr/hosts/corerun/corerun.cpp b/src/coreclr/hosts/corerun/corerun.cpp
index a5ce53aedd8b44..d6032091a94adc 100644
--- a/src/coreclr/hosts/corerun/corerun.cpp
+++ b/src/coreclr/hosts/corerun/corerun.cpp
@@ -286,6 +286,10 @@ size_t HOST_CONTRACT_CALLTYPE get_runtime_property(
 static char* s_core_libs_path = nullptr;
 static char* s_core_root_path = nullptr;
 
+#ifdef TARGET_BROWSER
+extern "C" bool BrowserHost_ExternalAssemblyProbe(const char* pathPtr, /*out*/ void **outDataStartPtr, /*out*/ int64_t* outSize);
+#endif // TARGET_BROWSER
+
 static bool HOST_CONTRACT_CALLTYPE get_native_code_data(
     const host_runtime_contract_native_code_context* context,
     host_runtime_contract_native_code_data* data)
@@ -343,6 +347,11 @@ static bool HOST_CONTRACT_CALLTYPE external_assembly_probe(
     void** data_start,
     int64_t* size)
 {
+#ifdef TARGET_BROWSER
+    if (BrowserHost_ExternalAssemblyProbe(path, data_start, size))
+        return true;
+#endif // TARGET_BROWSER
+
     // Get just the file name
     const char* name = path;
     const char* pos = strrchr(name, '/');
@@ -424,6 +433,9 @@ static int run(const configuration& config)
     string_t tpa_list;
     string_t app_assemblies_env = pal::getenv(envvar::appAssemblies);
     bool use_external_assembly_probe = false;
+#ifdef TARGET_BROWSER
+    use_external_assembly_probe = true;
+#endif // TARGET_BROWSER
     if (app_assemblies_env.empty() || app_assemblies_env == W("PROPERTY"))
     {
         // Use the TRUSTED_PLATFORM_ASSEMBLIES property to pass the app assemblies to the runtime.
diff --git a/src/coreclr/hosts/corerun/wasm/libCorerun.js b/src/coreclr/hosts/corerun/wasm/libCorerun.js
index 122ed7e217028d..31d051f8b75cf0 100644
--- a/src/coreclr/hosts/corerun/wasm/libCorerun.js
+++ b/src/coreclr/hosts/corerun/wasm/libCorerun.js
@@ -8,7 +8,7 @@ function libCoreRunFactory() {
         "$ENV",
         "$FS",
         "corerun_shutdown",
-        "BrowserHost_ShutdownDotnet",
+        "$UTF8ToString"
     ];
     if (LibraryManager.library.$NODEFS) {
         commonDeps.push("$NODEFS");
@@ -35,6 +35,62 @@ function libCoreRunFactory() {
         $CORERUN__postset: "CORERUN.selfInitialize()",
         $CORERUN__deps: commonDeps,
         BrowserHost_ShutdownDotnet: (exitCode) => _corerun_shutdown(exitCode),
+        BrowserHost_ExternalAssemblyProbe: (pathPtr, outDataStartPtr, outSize) => {
+            const path = UTF8ToString(pathPtr);
+            let wasmPath;
+            if (path.endsWith('.dll')) {
+                wasmPath = path.slice(0, -4) + '.wasm';
+            } else if (path.endsWith('.wasm')) {
+                wasmPath = path;
+            } else {
+                return false;
+            }
+
+            let wasmBytes;
+            try {
+                wasmBytes = FS.readFile(wasmPath);
+            } catch (e) {
+                return false;
+            }
+
+            // Synchronously instantiate the webcil WebAssembly module
+            const wasmModule = new WebAssembly.Module(wasmBytes);
+            const wasmInstance = new WebAssembly.Instance(wasmModule, {
+                webcil: { memory: wasmMemory }
+            });
+
+            const webcilVersion = wasmInstance.exports.webcilVersion.value;
+            if (webcilVersion !== 0) {
+                throw new Error(`Unsupported Webcil version: ${webcilVersion}`);
+            }
+
+            const sp = stackSave();
+            try {
+                const sizePtr = stackAlloc(4);
+                wasmInstance.exports.getWebcilSize(sizePtr);
+                const payloadSize = HEAPU32[sizePtr >>> 2];
+                if (payloadSize === 0) {
+                    throw new Error("Webcil payload size is 0");
+                }
+
+                const ptrPtr = stackAlloc(4);
+                if (_posix_memalign(ptrPtr, 16, payloadSize)) {
+                    throw new Error("posix_memalign failed for Webcil payload");
+                }
+                const payloadPtr = HEAPU32[ptrPtr >>> 2];
+
+                wasmInstance.exports.getWebcilPayload(payloadPtr, payloadSize);
+
+                // Write out parameters: void** data_start, int64_t* size
+                HEAPU32[outDataStartPtr >>> 2] = payloadPtr;
+                HEAPU32[outSize >>> 2] = payloadSize;
+                HEAPU32[(outSize + 4) >>> 2] = 0;
+
+                return true;
+            } finally {
+                stackRestore(sp);
+            }
+        }
     };
     const patchNODERAWFS = {
         cwd: () => {