diff --git a/chrome/browser/web_applications/jobs/manifest_to_web_app_install_info_job.cc b/chrome/browser/web_applications/jobs/manifest_to_web_app_install_info_job.cc
index 704b266b9cf8b..65c80a78793d6 100644
--- a/chrome/browser/web_applications/jobs/manifest_to_web_app_install_info_job.cc
+++ b/chrome/browser/web_applications/jobs/manifest_to_web_app_install_info_job.cc
@@ -837,6 +837,18 @@ void ManifestToWebAppInstallInfoJob::ParseManifestAndPopulateInfo() {
   GURL inferred_scope = install_info().scope.is_valid()
                             ? install_info().scope
                             : install_info().start_url().GetWithoutFilename();
+
+  // SECURITY: share_target.action arrives from the renderer with no
+  // browser-side validation (manifest_manager_host.cc does not check it, and
+  // ToWebAppShareTarget copies it directly). On ChromeOS this URL is later
+  // navigated to with a POST body containing user-shared data. A compromised
+  // renderer could supply a cross-origin action to exfiltrate that data.
+  // Gate it on IsInScope() exactly like lock_screen and note_taking below.
+  if (install_info().share_target.has_value() &&
+      !IsInScope(install_info().share_target->action, inferred_scope)) {
+    install_info().share_target = std::nullopt;
+  }
+
   if (base::FeatureList::IsEnabled(
           blink::features::kWebAppManifestLockScreen) &&
       manifest_->lock_screen && manifest_->lock_screen->start_url.is_valid() &&