diff --git a/packages/eslint-plugin/src/rules/array-type.ts b/packages/eslint-plugin/src/rules/array-type.ts
index e6e78b6e0f4d..1e3b978a2813 100644
--- a/packages/eslint-plugin/src/rules/array-type.ts
+++ b/packages/eslint-plugin/src/rules/array-type.ts
@@ -112,6 +112,7 @@ export default util.createRule<Options, MessageIds>({
             enum: ['array', 'generic', 'array-simple'],
           },
         },
+        additionalProperties: false,
         properties: {
           default: {
             $ref: '#/items/0/$defs/arrayOption',
diff --git a/packages/eslint-plugin/src/rules/ban-ts-comment.ts b/packages/eslint-plugin/src/rules/ban-ts-comment.ts
index 2c2e68855056..f3622c693ac9 100644
--- a/packages/eslint-plugin/src/rules/ban-ts-comment.ts
+++ b/packages/eslint-plugin/src/rules/ban-ts-comment.ts
@@ -53,6 +53,7 @@ export default util.createRule<[Options], MessageIds>({
               },
               {
                 type: 'object',
+                additionalProperties: false,
                 properties: {
                   descriptionFormat: { type: 'string' },
                 },
diff --git a/packages/eslint-plugin/src/rules/naming-convention-utils/schema.ts b/packages/eslint-plugin/src/rules/naming-convention-utils/schema.ts
index 0d092ea871d1..2cb6d9fed62b 100644
--- a/packages/eslint-plugin/src/rules/naming-convention-utils/schema.ts
+++ b/packages/eslint-plugin/src/rules/naming-convention-utils/schema.ts
@@ -40,6 +40,7 @@ const $DEFS: Record<string, JSONSchema.JSONSchema4> = {
   },
   matchRegexConfig: {
     type: 'object',
+    additionalProperties: false,
     properties: {
       match: { type: 'boolean' },
       regex: { type: 'string' },
diff --git a/packages/eslint-plugin/src/rules/no-misused-promises.ts b/packages/eslint-plugin/src/rules/no-misused-promises.ts
index 878a327982b1..3728d567621a 100644
--- a/packages/eslint-plugin/src/rules/no-misused-promises.ts
+++ b/packages/eslint-plugin/src/rules/no-misused-promises.ts
@@ -83,6 +83,7 @@ export default util.createRule<Options, MessageId>({
     schema: [
       {
         type: 'object',
+        additionalProperties: false,
         properties: {
           checksConditionals: {
             type: 'boolean',
diff --git a/packages/eslint-plugin/src/rules/no-unnecessary-type-assertion.ts b/packages/eslint-plugin/src/rules/no-unnecessary-type-assertion.ts
index 76fc59da74b2..589a257e572b 100644
--- a/packages/eslint-plugin/src/rules/no-unnecessary-type-assertion.ts
+++ b/packages/eslint-plugin/src/rules/no-unnecessary-type-assertion.ts
@@ -31,6 +31,7 @@ export default util.createRule<Options, MessageIds>({
     schema: [
       {
         type: 'object',
+        additionalProperties: false,
         properties: {
           typesToIgnore: {
             description: 'A list of type names to ignore.',
diff --git a/packages/eslint-plugin/src/rules/require-array-sort-compare.ts b/packages/eslint-plugin/src/rules/require-array-sort-compare.ts
index d38c032cb22b..f5628120c804 100644
--- a/packages/eslint-plugin/src/rules/require-array-sort-compare.ts
+++ b/packages/eslint-plugin/src/rules/require-array-sort-compare.ts
@@ -30,6 +30,7 @@ export default util.createRule<Options, MessageIds>({
     schema: [
       {
         type: 'object',
+        additionalProperties: false,
         properties: {
           ignoreStringArrays: {
             description:
diff --git a/packages/eslint-plugin/src/rules/restrict-template-expressions.ts b/packages/eslint-plugin/src/rules/restrict-template-expressions.ts
index e31807bfc1a8..32b670f47017 100644
--- a/packages/eslint-plugin/src/rules/restrict-template-expressions.ts
+++ b/packages/eslint-plugin/src/rules/restrict-template-expressions.ts
@@ -33,6 +33,7 @@ export default util.createRule<Options, MessageId>({
     schema: [
       {
         type: 'object',
+        additionalProperties: false,
         properties: {
           allowNumber: {
             description:
diff --git a/packages/eslint-plugin/src/rules/sort-type-constituents.ts b/packages/eslint-plugin/src/rules/sort-type-constituents.ts
index 81af9b1d9ec5..ec54153e988d 100644
--- a/packages/eslint-plugin/src/rules/sort-type-constituents.ts
+++ b/packages/eslint-plugin/src/rules/sort-type-constituents.ts
@@ -124,6 +124,7 @@ export default util.createRule<Options, MessageIds>({
     schema: [
       {
         type: 'object',
+        additionalProperties: false,
         properties: {
           checkIntersections: {
             description: 'Whether to check intersection types.',
diff --git a/packages/eslint-plugin/src/rules/typedef.ts b/packages/eslint-plugin/src/rules/typedef.ts
index bc95283b78c6..51820a11ef95 100644
--- a/packages/eslint-plugin/src/rules/typedef.ts
+++ b/packages/eslint-plugin/src/rules/typedef.ts
@@ -31,6 +31,7 @@ export default util.createRule<[Options], MessageIds>({
     schema: [
       {
         type: 'object',
+        additionalProperties: false,
         properties: {
           [OptionKeys.ArrayDestructuring]: { type: 'boolean' },
           [OptionKeys.ArrowParameter]: { type: 'boolean' },
diff --git a/packages/eslint-plugin/tests/schema-snapshots/array-type.shot b/packages/eslint-plugin/tests/schema-snapshots/array-type.shot
index da76d7036a86..4fef7c8ec978 100644
--- a/packages/eslint-plugin/tests/schema-snapshots/array-type.shot
+++ b/packages/eslint-plugin/tests/schema-snapshots/array-type.shot
@@ -11,6 +11,7 @@ exports[`Rule schemas should be convertible to TS types for documentation purpos
         "enum": ["array", "array-simple", "generic"]
       }
     },
+    "additionalProperties": false,
     "properties": {
       "default": {
         "$ref": "#/items/0/$defs/arrayOption",
diff --git a/packages/eslint-plugin/tests/schema-snapshots/ban-ts-comment.shot b/packages/eslint-plugin/tests/schema-snapshots/ban-ts-comment.shot
index e754ff98ae5d..ee076d804daa 100644
--- a/packages/eslint-plugin/tests/schema-snapshots/ban-ts-comment.shot
+++ b/packages/eslint-plugin/tests/schema-snapshots/ban-ts-comment.shot
@@ -17,6 +17,7 @@ exports[`Rule schemas should be convertible to TS types for documentation purpos
             "enum": ["allow-with-description"]
           },
           {
+            "additionalProperties": false,
             "properties": {
               "descriptionFormat": {
                 "type": "string"
diff --git a/packages/eslint-plugin/tests/schema-snapshots/naming-convention.shot b/packages/eslint-plugin/tests/schema-snapshots/naming-convention.shot
index c97b0eefc220..1f360bc55c29 100644
--- a/packages/eslint-plugin/tests/schema-snapshots/naming-convention.shot
+++ b/packages/eslint-plugin/tests/schema-snapshots/naming-convention.shot
@@ -21,6 +21,7 @@ exports[`Rule schemas should be convertible to TS types for documentation purpos
       ]
     },
     "matchRegexConfig": {
+      "additionalProperties": false,
       "properties": {
         "match": {
           "type": "boolean"
diff --git a/packages/eslint-plugin/tests/schema-snapshots/no-misused-promises.shot b/packages/eslint-plugin/tests/schema-snapshots/no-misused-promises.shot
index be4e2d561120..2ba6191f4645 100644
--- a/packages/eslint-plugin/tests/schema-snapshots/no-misused-promises.shot
+++ b/packages/eslint-plugin/tests/schema-snapshots/no-misused-promises.shot
@@ -6,6 +6,7 @@ exports[`Rule schemas should be convertible to TS types for documentation purpos
 
 [
   {
+    "additionalProperties": false,
     "properties": {
       "checksConditionals": {
         "type": "boolean"
diff --git a/packages/eslint-plugin/tests/schema-snapshots/no-unnecessary-type-assertion.shot b/packages/eslint-plugin/tests/schema-snapshots/no-unnecessary-type-assertion.shot
index 29683a8039ce..b0954ae493bc 100644
--- a/packages/eslint-plugin/tests/schema-snapshots/no-unnecessary-type-assertion.shot
+++ b/packages/eslint-plugin/tests/schema-snapshots/no-unnecessary-type-assertion.shot
@@ -6,6 +6,7 @@ exports[`Rule schemas should be convertible to TS types for documentation purpos
 
 [
   {
+    "additionalProperties": false,
     "properties": {
       "typesToIgnore": {
         "description": "A list of type names to ignore.",
diff --git a/packages/eslint-plugin/tests/schema-snapshots/require-array-sort-compare.shot b/packages/eslint-plugin/tests/schema-snapshots/require-array-sort-compare.shot
index 938d7b6887a3..979a80507162 100644
--- a/packages/eslint-plugin/tests/schema-snapshots/require-array-sort-compare.shot
+++ b/packages/eslint-plugin/tests/schema-snapshots/require-array-sort-compare.shot
@@ -6,6 +6,7 @@ exports[`Rule schemas should be convertible to TS types for documentation purpos
 
 [
   {
+    "additionalProperties": false,
     "properties": {
       "ignoreStringArrays": {
         "description": "Whether to ignore arrays in which all elements are strings.",
diff --git a/packages/eslint-plugin/tests/schema-snapshots/restrict-template-expressions.shot b/packages/eslint-plugin/tests/schema-snapshots/restrict-template-expressions.shot
index a5af1c8d0630..194ddc4260cb 100644
--- a/packages/eslint-plugin/tests/schema-snapshots/restrict-template-expressions.shot
+++ b/packages/eslint-plugin/tests/schema-snapshots/restrict-template-expressions.shot
@@ -6,6 +6,7 @@ exports[`Rule schemas should be convertible to TS types for documentation purpos
 
 [
   {
+    "additionalProperties": false,
     "properties": {
       "allowAny": {
         "description": "Whether to allow \`any\` typed values in template expressions.",
diff --git a/packages/eslint-plugin/tests/schema-snapshots/sort-type-constituents.shot b/packages/eslint-plugin/tests/schema-snapshots/sort-type-constituents.shot
index d84cff0e09d6..3384c8b4d50e 100644
--- a/packages/eslint-plugin/tests/schema-snapshots/sort-type-constituents.shot
+++ b/packages/eslint-plugin/tests/schema-snapshots/sort-type-constituents.shot
@@ -6,6 +6,7 @@ exports[`Rule schemas should be convertible to TS types for documentation purpos
 
 [
   {
+    "additionalProperties": false,
     "properties": {
       "checkIntersections": {
         "description": "Whether to check intersection types.",
diff --git a/packages/eslint-plugin/tests/schema-snapshots/typedef.shot b/packages/eslint-plugin/tests/schema-snapshots/typedef.shot
index d08f373ab797..e244ad4d80ca 100644
--- a/packages/eslint-plugin/tests/schema-snapshots/typedef.shot
+++ b/packages/eslint-plugin/tests/schema-snapshots/typedef.shot
@@ -6,6 +6,7 @@ exports[`Rule schemas should be convertible to TS types for documentation purpos
 
 [
   {
+    "additionalProperties": false,
     "properties": {
       "arrayDestructuring": {
         "type": "boolean"
diff --git a/packages/rule-schema-to-typescript-types/src/generateObjectType.ts b/packages/rule-schema-to-typescript-types/src/generateObjectType.ts
index 9ff4b928dcd7..c0de43699d36 100644
--- a/packages/rule-schema-to-typescript-types/src/generateObjectType.ts
+++ b/packages/rule-schema-to-typescript-types/src/generateObjectType.ts
@@ -13,13 +13,16 @@ export function generateObjectType(
   const commentLines = getCommentLines(schema);
 
   let indexSignature: AST | null = null;
-  if (schema.additionalProperties === true) {
+  if (
+    schema.additionalProperties === true ||
+    schema.additionalProperties === undefined
+  ) {
     indexSignature = {
       type: 'type-reference',
       typeName: 'unknown',
       commentLines: [],
     };
-  } else if (schema.additionalProperties) {
+  } else if (typeof schema.additionalProperties === 'object') {
     const indexSigType = generateType(schema.additionalProperties, refMap);
     indexSignature = indexSigType;
   }