diff --git a/core/src/utils/sanitization/index.ts b/core/src/utils/sanitization/index.ts
index bb851fea7e0..2ee633f4a6f 100644
--- a/core/src/utils/sanitization/index.ts
+++ b/core/src/utils/sanitization/index.ts
@@ -36,8 +36,12 @@ export const sanitizeDOMString = (untrustedString: IonicSafeString | string | un
      * fragment in Chrome. If a string
      * contains onload then we should not
      * attempt to add this to the fragment.
+     *
+     * HTML attribute names are case-insensitive and may have whitespace
+     * around the `=`, so match those variants too (e.g. `onLoad=`,
+     * `ONLOAD =`) instead of only the exact lowercase `onload=` substring.
      */
-    if (untrustedString.includes('onload=')) {
+    if (/onload\s*=/i.test(untrustedString)) {
       return '';
     }
 
diff --git a/core/src/utils/sanitization/test/sanitization.spec.ts b/core/src/utils/sanitization/test/sanitization.spec.ts
index 2ca069e387f..03c2abf7c48 100644
--- a/core/src/utils/sanitization/test/sanitization.spec.ts
+++ b/core/src/utils/sanitization/test/sanitization.spec.ts
@@ -26,6 +26,21 @@ describe('sanitizeDOMString', () => {
     ).toEqual('<button id="myButton" name="myButton">harmless button</button>');
   });
 
+  it('filter onload regardless of case or whitespace around =', () => {
+    /**
+     * onload is blocked with an upfront string check (rather than the
+     * attribute-stripping pass used for onerror/onclick above) because it
+     * can fire synchronously while the untrusted string is being parsed
+     * into the working document fragment, before that pass runs. HTML
+     * attribute names are case-insensitive and may have whitespace around
+     * `=`, so the check must not be a plain lowercase substring match.
+     */
+    expect(sanitizeDOMString('<svg onload=alert(document.cookie)>')).toEqual('');
+    expect(sanitizeDOMString('<svg onLoad=alert(document.cookie)>')).toEqual('');
+    expect(sanitizeDOMString('<svg ONLOAD=alert(document.cookie)>')).toEqual('');
+    expect(sanitizeDOMString('<svg onload =alert(document.cookie)>')).toEqual('');
+  });
+
   it('filter <a> href JS', () => {
     expect(sanitizeDOMString('<a href="javascript:alert(document.cookie)">harmless link</a>')).toEqual(
       '<a>harmless link</a>'