diff --git a/chrome/browser/ui/webui/updater/updater_page_handler.cc b/chrome/browser/ui/webui/updater/updater_page_handler.cc
index a99a9f384125d..fd78c9ef90d2c 100644
--- a/chrome/browser/ui/webui/updater/updater_page_handler.cc
+++ b/chrome/browser/ui/webui/updater/updater_page_handler.cc
@@ -14,6 +14,7 @@
 
 #include "base/barrier_closure.h"
 #include "base/containers/flat_map.h"
+#include "base/files/file.h"
 #include "base/files/file_enumerator.h"
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
@@ -226,7 +227,14 @@ void UnzipUpdaterHistoryFilesImpl(
   }
 
   base::FilePath archive_path = temp_dir.GetPath().AppendASCII("input.zip");
-  if (!base::WriteFile(archive_path, zip_data)) {
+  // FLAG_CREATE -> O_CREAT|O_EXCL on POSIX: refuses to open through a
+  // pre-existing dentry (including a symlink planted by another process that
+  // shares the temp directory), so the user-supplied bytes can only land in a
+  // freshly-created regular file inside the just-mkdtemp'd directory.
+  base::File archive(archive_path,
+                     base::File::FLAG_CREATE | base::File::FLAG_WRITE);
+  if (!archive.IsValid() ||
+      !archive.WriteAtCurrentPosAndCheck(base::span(zip_data))) {
     std::move(callback).Run(
         base::unexpected(updater_ui::mojom::UnzipUpdaterHistoryFilesError::New(
             "Failed to write user-supplied zip data to storage")));