diff --git a/.changeset/nasty-peas-agree.md b/.changeset/nasty-peas-agree.md
new file mode 100644
index 0000000000..1b5de8eddb
--- /dev/null
+++ b/.changeset/nasty-peas-agree.md
@@ -0,0 +1,6 @@
+---
+'@redocly/openapi-core': patch
+'@redocly/cli': patch
+---
+
+Updated `no-required-schema-properties-undefined` rule to cover additional edge cases.
diff --git a/docs/@v1/rules/oas/no-required-schema-properties-undefined.md b/docs/@v1/rules/oas/no-required-schema-properties-undefined.md
index 90a4f3ed6e..4f2f5199e2 100644
--- a/docs/@v1/rules/oas/no-required-schema-properties-undefined.md
+++ b/docs/@v1/rules/oas/no-required-schema-properties-undefined.md
@@ -98,6 +98,86 @@ schemas:
       - Name
 ```
 
+The rule accepts bare `required` constraints on property sub-schemas when the property's type is defined in a parent `allOf` sibling. This is a valid JSON Schema pattern for adding presence constraints on top of a referenced base type:
+
+```yaml
+schemas:
+  PersonBase:
+    type: object
+    properties:
+      personName:
+        type: object
+        properties:
+          givenName:
+            type: string
+          familyName:
+            type: string
+  Person:
+    type: object
+    allOf:
+      - $ref: '#/components/schemas/PersonBase'
+    properties:
+      personName:
+        required:
+          - givenName
+          - familyName
+    required:
+      - personName
+```
+
+The rule also accepts `oneOf` branches used as pure constraint fragments, where each branch contains only a `required` keyword and the property's type is defined in a parent `allOf` sibling:
+
+```yaml
+schemas:
+  PersonBase:
+    type: object
+    properties:
+      communication:
+        type: object
+        properties:
+          landlines:
+            type: array
+          mobiles:
+            type: array
+          emails:
+            type: array
+  Person:
+    type: object
+    allOf:
+      - $ref: '#/components/schemas/PersonBase'
+    properties:
+      communication:
+        oneOf:
+          - required:
+              - landlines
+          - required:
+              - mobiles
+          - required:
+              - emails
+    required:
+      - communication
+```
+
+Misspellings in bare `required` lists are still caught. If a required key does not exist in the property's type definition resolved through the parent `allOf` sibling, the rule reports an error:
+
+```yaml
+schemas:
+  Person:
+    type: object
+    allOf:
+      - $ref: '#/components/schemas/PersonBase'
+    properties:
+      personName:
+        required:
+          - giveName # misspelling of givenName
+    required:
+      - personName
+```
+
+```bash
+Required property 'giveName' is undefined.
+```
+
 ## Related rules
 
 - [no-invalid-schema-examples](./no-invalid-schema-examples.md)
diff --git a/docs/@v2/rules/common/no-required-schema-properties-undefined.md b/docs/@v2/rules/common/no-required-schema-properties-undefined.md
index 3ca3bffe9a..04abf81f4e 100644
--- a/docs/@v2/rules/common/no-required-schema-properties-undefined.md
+++ b/docs/@v2/rules/common/no-required-schema-properties-undefined.md
@@ -128,6 +128,86 @@ schemas:
         example: doggie
 ```
 
+The rule accepts bare `required` constraints on property sub-schemas when the property's type is defined in a parent `allOf` sibling. This is a valid JSON Schema pattern for adding presence constraints on top of a referenced base type:
+
+```yaml
+schemas:
+  PersonBase:
+    type: object
+    properties:
+      personName:
+        type: object
+        properties:
+          givenName:
+            type: string
+          familyName:
+            type: string
+  Person:
+    type: object
+    allOf:
+      - $ref: '#/components/schemas/PersonBase'
+    properties:
+      personName:
+        required:
+          - givenName
+          - familyName
+    required:
+      - personName
+```
+
+The rule also accepts `oneOf` branches used as pure constraint fragments, where each branch contains only a `required` keyword and the property's type is defined in a parent `allOf` sibling:
+
+```yaml
+schemas:
+  PersonBase:
+    type: object
+    properties:
+      communication:
+        type: object
+        properties:
+          landlines:
+            type: array
+          mobiles:
+            type: array
+          emails:
+            type: array
+  Person:
+    type: object
+    allOf:
+      - $ref: '#/components/schemas/PersonBase'
+    properties:
+      communication:
+        oneOf:
+          - required:
+              - landlines
+          - required:
+              - mobiles
+          - required:
+              - emails
+    required:
+      - communication
+```
+
+Misspellings in bare `required` lists are still caught. If a required key does not exist in the property's type definition resolved through the parent `allOf` sibling, the rule reports an error:
+
+```yaml
+schemas:
+  Person:
+    type: object
+    allOf:
+      - $ref: '#/components/schemas/PersonBase'
+    properties:
+      personName:
+        required:
+          - giveName # misspelling of givenName
+    required:
+      - personName
+```
+
+```bash
+Required property 'giveName' is undefined.
+```
+
 ## Related rules
 
 - [no-schema-type-mismatch](./no-schema-type-mismatch.md)
diff --git a/packages/core/src/rules/common/__tests__/no-required-schema-properties-undefined.test.ts b/packages/core/src/rules/common/__tests__/no-required-schema-properties-undefined.test.ts
index 04167ac42d..bf909a7d26 100644
--- a/packages/core/src/rules/common/__tests__/no-required-schema-properties-undefined.test.ts
+++ b/packages/core/src/rules/common/__tests__/no-required-schema-properties-undefined.test.ts
@@ -46,7 +46,7 @@ describe('no-required-schema-properties-undefined', () => {
               "source": "foobar.yaml",
             },
           ],
-          "message": "Required property 'test' is not defined.",
+          "message": "Required property 'test' is undefined.",
           "ruleId": "no-required-schema-properties-undefined",
           "severity": "error",
           "suggest": [],
@@ -59,7 +59,7 @@ describe('no-required-schema-properties-undefined', () => {
               "source": "foobar.yaml",
             },
           ],
-          "message": "Required property 'test2' is not defined.",
+          "message": "Required property 'test2' is undefined.",
           "ruleId": "no-required-schema-properties-undefined",
           "severity": "error",
           "suggest": [],
@@ -108,7 +108,7 @@ describe('no-required-schema-properties-undefined', () => {
               "source": "foobar.yaml",
             },
           ],
-          "message": "Required property 'test' is not defined.",
+          "message": "Required property 'test' is undefined.",
           "ruleId": "no-required-schema-properties-undefined",
           "severity": "error",
           "suggest": [],
@@ -231,7 +231,7 @@ describe('no-required-schema-properties-undefined', () => {
               "source": "foobar.yaml",
             },
           ],
-          "message": "Required property 'foo' is not defined.",
+          "message": "Required property 'foo' is undefined.",
           "ruleId": "no-required-schema-properties-undefined",
           "severity": "error",
           "suggest": [],
@@ -286,7 +286,7 @@ describe('no-required-schema-properties-undefined', () => {
               "source": "foobar.yaml",
             },
           ],
-          "message": "Required property 'surname' is not defined.",
+          "message": "Required property 'surname' is undefined.",
           "ruleId": "no-required-schema-properties-undefined",
           "severity": "error",
           "suggest": [],
@@ -428,7 +428,7 @@ describe('no-required-schema-properties-undefined', () => {
               "source": "foobar.yaml",
             },
           ],
-          "message": "Required property 'test' is not defined.",
+          "message": "Required property 'test' is undefined.",
           "ruleId": "no-required-schema-properties-undefined",
           "severity": "error",
           "suggest": [],
@@ -536,7 +536,7 @@ describe('no-required-schema-properties-undefined', () => {
               "source": "foobar.yaml",
             },
           ],
-          "message": "Required property 'name' is not defined.",
+          "message": "Required property 'name' is undefined.",
           "ruleId": "no-required-schema-properties-undefined",
           "severity": "error",
           "suggest": [],
@@ -648,7 +648,7 @@ describe('no-required-schema-properties-undefined', () => {
               "source": "foobar.yaml",
             },
           ],
-          "message": "Required property 'name' is not defined.",
+          "message": "Required property 'name' is undefined.",
           "ruleId": "no-required-schema-properties-undefined",
           "severity": "error",
           "suggest": [],
@@ -661,7 +661,7 @@ describe('no-required-schema-properties-undefined', () => {
               "source": "foobar.yaml",
             },
           ],
-          "message": "Required property 'huntingSkill' is not defined.",
+          "message": "Required property 'huntingSkill' is undefined.",
           "ruleId": "no-required-schema-properties-undefined",
           "severity": "error",
           "suggest": [],
@@ -796,7 +796,7 @@ describe('no-required-schema-properties-undefined', () => {
               "source": "foobar.yaml",
             },
           ],
-          "message": "Required property 'missing-required-prop' is not defined.",
+          "message": "Required property 'missing-required-prop' is undefined.",
           "ruleId": "no-required-schema-properties-undefined",
           "severity": "error",
           "suggest": [],
@@ -841,7 +841,7 @@ describe('no-required-schema-properties-undefined', () => {
               "source": "foobar.yaml",
             },
           ],
-          "message": "Required property 'missingRequired' is not defined.",
+          "message": "Required property 'missingRequired' is undefined.",
           "ruleId": "no-required-schema-properties-undefined",
           "severity": "error",
           "suggest": [],
@@ -889,7 +889,194 @@ describe('no-required-schema-properties-undefined', () => {
               "source": "foobar.yaml",
             },
           ],
-          "message": "Required property 'missing-required' is not defined.",
+          "message": "Required property 'missing-required' is undefined.",
+          "ruleId": "no-required-schema-properties-undefined",
+          "severity": "error",
+          "suggest": [],
+        },
+      ]
+    `);
+  });
+
+  it('should not report bare required when property is defined in parent allOf sibling', async () => {
+    const document = parseYamlToDocument(
+      outdent`
+          openapi: 3.0.0
+          components:
+            schemas:
+              PersonBase:
+                type: object
+                properties:
+                  personName:
+                    type: object
+                    properties:
+                      givenName:
+                        type: string
+                      familyName:
+                        type: string
+              Person:
+                type: object
+                allOf:
+                  - $ref: '#/components/schemas/PersonBase'
+                properties:
+                  personName:
+                    required:
+                      - givenName
+                      - familyName
+                required:
+                  - personName
+        `,
+      'foobar.yaml'
+    );
+
+    const results = await lintDocument({
+      externalRefResolver: new BaseResolver(),
+      document,
+      config: await createConfig({ rules: { 'no-required-schema-properties-undefined': 'error' } }),
+    });
+
+    expect(replaceSourceWithRef(results)).toMatchInlineSnapshot(`[]`);
+  });
+
+  it('should not report bare required in oneOf branches when property is defined in parent allOf sibling', async () => {
+    const document = parseYamlToDocument(
+      outdent`
+          openapi: 3.0.0
+          components:
+            schemas:
+              PersonBase:
+                type: object
+                properties:
+                  communication:
+                    type: object
+                    properties:
+                      landlines:
+                        type: array
+                      mobiles:
+                        type: array
+                      emails:
+                        type: array
+              Person:
+                type: object
+                allOf:
+                  - $ref: '#/components/schemas/PersonBase'
+                properties:
+                  communication:
+                    oneOf:
+                      - required:
+                          - landlines
+                      - required:
+                          - mobiles
+                      - required:
+                          - emails
+                required:
+                  - communication
+        `,
+      'foobar.yaml'
+    );
+
+    const results = await lintDocument({
+      externalRefResolver: new BaseResolver(),
+      document,
+      config: await createConfig({ rules: { 'no-required-schema-properties-undefined': 'error' } }),
+    });
+
+    expect(replaceSourceWithRef(results)).toMatchInlineSnapshot(`[]`);
+  });
+
+  it('should not report bare required in anyOf branches when property is defined in parent allOf sibling', async () => {
+    const document = parseYamlToDocument(
+      outdent`
+          openapi: 3.0.0
+          components:
+            schemas:
+              PersonBase:
+                type: object
+                properties:
+                  communication:
+                    type: object
+                    properties:
+                      landlines:
+                        type: array
+                      mobiles:
+                        type: array
+                      emails:
+                        type: array
+              Person:
+                type: object
+                allOf:
+                  - $ref: '#/components/schemas/PersonBase'
+                properties:
+                  communication:
+                    anyOf:
+                      - required:
+                          - landlines
+                      - required:
+                          - mobiles
+                      - required:
+                          - emails
+                required:
+                  - communication
+        `,
+      'foobar.yaml'
+    );
+
+    const results = await lintDocument({
+      externalRefResolver: new BaseResolver(),
+      document,
+      config: await createConfig({ rules: { 'no-required-schema-properties-undefined': 'error' } }),
+    });
+
+    expect(replaceSourceWithRef(results)).toMatchInlineSnapshot(`[]`);
+  });
+
+  it('should report misspelled required property even when parent allOf sibling defines the property', async () => {
+    const document = parseYamlToDocument(
+      outdent`
+          openapi: 3.0.0
+          components:
+            schemas:
+              PersonBase:
+                type: object
+                properties:
+                  personName:
+                    type: object
+                    properties:
+                      givenName:
+                        type: string
+                      familyName:
+                        type: string
+              Person:
+                type: object
+                allOf:
+                  - $ref: '#/components/schemas/PersonBase'
+                properties:
+                  personName:
+                    required:
+                      - giveName
+                required:
+                  - personName
+        `,
+      'foobar.yaml'
+    );
+
+    const results = await lintDocument({
+      externalRefResolver: new BaseResolver(),
+      document,
+      config: await createConfig({ rules: { 'no-required-schema-properties-undefined': 'error' } }),
+    });
+
+    expect(replaceSourceWithRef(results)).toMatchInlineSnapshot(`
+      [
+        {
+          "location": [
+            {
+              "pointer": "#/components/schemas/Person/properties/personName/required/0",
+              "reportOnKey": false,
+              "source": "foobar.yaml",
+            },
+          ],
+          "message": "Required property 'giveName' is undefined.",
           "ruleId": "no-required-schema-properties-undefined",
           "severity": "error",
           "suggest": [],
@@ -929,7 +1116,7 @@ describe('no-required-schema-properties-undefined', () => {
               "source": "foobar.yaml",
             },
           ],
-          "message": "Required property 'name' is not defined.",
+          "message": "Required property 'name' is undefined.",
           "ruleId": "no-required-schema-properties-undefined",
           "severity": "error",
           "suggest": [],
diff --git a/packages/core/src/rules/common/no-required-schema-properties-undefined.ts b/packages/core/src/rules/common/no-required-schema-properties-undefined.ts
index c8751b2622..082d7e24f0 100644
--- a/packages/core/src/rules/common/no-required-schema-properties-undefined.ts
+++ b/packages/core/src/rules/common/no-required-schema-properties-undefined.ts
@@ -81,13 +81,50 @@ export const NoRequiredSchemaPropertiesUndefined:
 
         const compositionRoot = findCompositionRoot(parents.length - 2, currentSchema);
 
+        const hasPropertyInParentContext = (
+          propertyName: string,
+          targetSchema: AnySchema
+        ): boolean => {
+          for (let i = parents.length - 2; i >= 0; i--) {
+            const ancestor = parents[i];
+            const props = ancestor.properties as Record<string, AnySchema> | undefined;
+            if (!props) continue;
+
+            const propKey = (Object.keys(props) as string[]).find((k) => {
+              const val = getOwn(props, k) as AnySchema;
+              if (val === targetSchema) return true;
+              return resolveSchema(val, ctx).schema === targetSchema;
+            });
+            if (!propKey) continue;
+
+            const checkSiblings = (siblings: AnySchema[] | undefined): boolean =>
+              !!siblings?.some((sibling) => {
+                const { schema: s, location } = resolveSchema(sibling, ctx);
+                if (!s?.properties) return false;
+                const propDef = getOwn(s.properties as Record<string, AnySchema>, propKey);
+                if (propDef === undefined) return false;
+                return hasProperty(propDef as AnySchema, propertyName, new Set(), location);
+              });
+
+            if (
+              checkSiblings(ancestor.allOf) ||
+              checkSiblings(ancestor.anyOf) ||
+              checkSiblings(ancestor.oneOf)
+            ) {
+              return true;
+            }
+          }
+          return false;
+        };
+
         for (const [i, requiredProperty] of currentSchema.required.entries()) {
           if (
             !hasProperty(currentSchema, requiredProperty, new Set()) &&
-            !hasProperty(compositionRoot, requiredProperty, new Set())
+            !hasProperty(compositionRoot, requiredProperty, new Set()) &&
+            !hasPropertyInParentContext(requiredProperty, compositionRoot ?? currentSchema)
           ) {
             ctx.report({
-              message: `Required property '${requiredProperty}' is not defined.`,
+              message: `Required property '${requiredProperty}' is undefined.`,
               location: ctx.location.child(['required', i]),
             });
           }