fix(notifications): allowlist local inline image sources

The http(s)-only regex let protocol-relative //host, ftp, data and
entity-encoded schemes through, and the comment overstated what it
removed. Replace it with a deny-by-default allowlist: an <img> is
removed unless its src, entities decoded first, is a file: URL or a
single leading slash. Protocol-relative //host is rejected while a
/absolute/path is kept.

1 files changed, 22 insertions, 5 deletions

diff --git a/shared/Notify.qml b/shared/Notify.qml
index c79f5f5..237d8c9 100644
--- a/shared/Notify.qml
+++ b/shared/Notify.qml
@@ -66,13 +66,30 @@ Singleton {
     function close(id) { root.run(["close", String(id)]); }
     function closeAll() { root.run(["close-all"]); }
 
-    // Inline images are local only. A notification is untrusted input, and a
-    // remote <img src> would otherwise make the shell fetch a URL, which leaks
-    // that the notification was shown. This removes such tags before the
-    // RichText body renders; a local path or file:// source is left alone.
+    // Inline images are local only. A notification is untrusted input, and any
+    // remote <img src> (http(s), protocol-relative //host, ftp, data, or an
+    // entity-encoded scheme) would make the shell fetch or embed something the
+    // sender chose, which leaks that the notification was shown. Deny by
+    // default: a tag survives only if its src decodes to a file: URL or a
+    // leading-slash absolute path. Entities are decoded before the test, so an
+    // encoded scheme cannot slip past.
     function sanitize(body) {
-        return (body || "").replace(/<img\b[^>]*\bsrc\s*=\s*["']?\s*https?:\/\/[^>]*>/gi, "");
+        function decode(s) {
+            return s.replace(/&(?:#x([0-9a-f]+)|#(\d+)|(amp|colon|sol|tab|quot));/gi,
+                function (m, hex, dec, name) {
+                    if (hex !== undefined) return String.fromCharCode(parseInt(hex, 16));
+                    if (dec !== undefined) return String.fromCharCode(parseInt(dec, 10));
+                    return { amp: "&", colon: ":", sol: "/", tab: "\t", quot: "\"" }[name.toLowerCase()];
+                });
+        }
+        return (body || "").replace(/<img\b[^>]*>/gi, function (tag) {
+            const m = tag.match(/\bsrc\s*=\s*(?:"([^"]*)"|'([^']*)'|([^\s>]+))/i);
+            if (!m) return "";
+            const src = decode(m[1] !== undefined ? m[1] : m[2] !== undefined ? m[2] : m[3]);
+            return /^file:/i.test(src) || (src.charAt(0) === "/" && src.charAt(1) !== "/") ? tag : "";
+        });
     }
+
     function action(id, key) { root.run(["action", String(id), key]); }
     function clearHistory() { root.run(["clear-history"]); }