diff --git a/scripts/validate-community-people.mjs b/scripts/validate-community-people.mjs
index 78b4d55c..a7d5c3c2 100644
--- a/scripts/validate-community-people.mjs
+++ b/scripts/validate-community-people.mjs
@@ -37,23 +37,52 @@ if (!ISO_8601.test(data.fetchedAt ?? '')) {
 // back to name for the one member without one), so a stale or
 // partially-generated file with the right shape but a missing/extra person
 // fails loudly instead of only checking that the arrays are non-empty.
-for (const [section, rosterEntries] of Object.entries(roster.sections || {})) {
-  const generated = data.people?.[section] || [];
-  const key = (person) => person.github || person.name;
-  const rosterKeys = new Set(rosterEntries.map(key));
-  const generatedKeys = new Set(generated.map(key));
-  for (const entry of rosterEntries) {
-    if (!generatedKeys.has(key(entry))) {
-      collectError(
-        errors,
-        `people.${section}`,
-        'error',
-        `missing roster member ${entry.name}`,
-      );
+//
+// The loop runs over the union of both files' section keys, not the roster's
+// alone. Every section in the generated file is rendered by
+// <CommunityPeople section="..." />, so driving the loop from the roster let a
+// section present only in community-people.json skip every check below --
+// including the profileImageUrl() host gate, which is the last thing standing
+// between an unattended upstream refresh and an arbitrary third-party host in
+// an <img src> served to every visitor.
+const rosterSections = roster.sections || {};
+const generatedSections = data.people || {};
+const key = (person) => person.github || person.name;
+
+for (const section of new Set([
+  ...Object.keys(rosterSections),
+  ...Object.keys(generatedSections),
+])) {
+  const onRoster = Object.hasOwn(rosterSections, section);
+  const rosterEntries = onRoster ? rosterSections[section] || [] : [];
+  const generated = generatedSections[section] || [];
+
+  if (!onRoster) {
+    collectError(
+      errors,
+      `people.${section}`,
+      'error',
+      'section is not declared in community-roster.json; every section the site renders must be on the roster',
+    );
+  } else {
+    const generatedKeys = new Set(generated.map(key));
+    for (const entry of rosterEntries) {
+      if (!generatedKeys.has(key(entry))) {
+        collectError(
+          errors,
+          `people.${section}`,
+          'error',
+          `missing roster member ${entry.name}`,
+        );
+      }
     }
   }
+
+  const rosterKeys = new Set(rosterEntries.map(key));
   for (const person of generated) {
-    if (!rosterKeys.has(key(person))) {
+    // Skipped when the whole section is unknown: the section error above
+    // already says so, once, instead of once per member.
+    if (onRoster && !rosterKeys.has(key(person))) {
       collectError(
         errors,
         `people.${section}`,
diff --git a/tests/validate-community-people.test.mjs b/tests/validate-community-people.test.mjs
index b5f503f5..fafa118b 100644
--- a/tests/validate-community-people.test.mjs
+++ b/tests/validate-community-people.test.mjs
@@ -258,10 +258,92 @@ test('reports a missing fetchedAt instead of crashing on an absent field', () =>
   assert.doesNotMatch(result.stderr, /TypeError/);
 });
 
-test('treats a roster with no sections as having nothing to cross-check', () => {
+test('rejects a generated section the roster does not declare', () => {
   const result = runScriptWithFixtures(SCRIPT, fixture(freshData, {}));
+  assert.equal(result.status, 1);
+  assert.match(
+    result.stderr,
+    /people\.tab.*section is not declared in community-roster\.json/,
+  );
+  assert.match(
+    result.stderr,
+    /people\.staff.*section is not declared in community-roster\.json/,
+  );
+});
+
+// The hole this guards: a section present only in the generated file used to
+// skip the loop body entirely, so its members reached <img src> with no host
+// check at all.
+test('gates images in a generated section the roster does not declare', () => {
+  const result = runScriptWithFixtures(
+    SCRIPT,
+    fixture({
+      ...freshData,
+      people: {
+        ...freshData.people,
+        ambassadors: [
+          validPerson({
+            name: 'Probe',
+            github: 'probe',
+            image: 'https://evil.example/beacon.png',
+          }),
+        ],
+      },
+    }),
+  );
+  assert.equal(result.status, 1);
+  assert.match(
+    result.stderr,
+    /people\.ambassadors.*section is not declared in community-roster\.json/,
+  );
+  assert.match(
+    result.stderr,
+    /Probe image must be an https URL on an allowed host/,
+  );
+});
+
+// A section the roster does not declare is reported once, as a section error,
+// rather than once per member as "is not on the roster".
+test('does not repeat the roster-membership error for an undeclared section', () => {
+  const result = runScriptWithFixtures(
+    SCRIPT,
+    fixture({
+      ...freshData,
+      people: { ...freshData.people, ambassadors: [validPerson()] },
+    }),
+  );
+  assert.equal(result.status, 1);
+  assert.doesNotMatch(
+    result.stderr,
+    /people\.ambassadors.*is not on the roster/,
+  );
+});
+
+test('still cross-checks roster membership within a declared section', () => {
+  const result = runScriptWithFixtures(
+    SCRIPT,
+    fixture({
+      ...freshData,
+      people: {
+        tab: [validPerson(), validPerson({ name: 'Mallory', github: 'mal' })],
+        staff: [staffPerson()],
+      },
+    }),
+  );
+  assert.equal(result.status, 1);
+  assert.match(result.stderr, /Mallory is not on the roster/);
+});
+
+test('treats a declared roster section with no entries as empty', () => {
+  const result = runScriptWithFixtures(
+    SCRIPT,
+    fixture(
+      { ...freshData, people: { ...freshData.people, alumni: [] } },
+      { sections: { ...roster.sections, alumni: null } },
+    ),
+  );
   assert.equal(result.status, 0, result.stderr);
-  assert.match(result.stdout, /Validated 2 community profiles/);
+  assert.doesNotMatch(result.stderr, /TypeError/);
 });
 
 test('treats a section absent from the generated file as empty', () => {