diff --git a/README.md b/README.md
index 574c7668..fb821a71 100644
--- a/README.md
+++ b/README.md
@@ -315,7 +315,6 @@ The following tests are not yet implemented and therefore missing:
 - Mandatory Test 6.1.10
 - Mandatory Test 6.1.14
 - Mandatory Test 6.1.16
-- Mandatory Test 6.1.27.12
 - Mandatory Test 6.1.27.13
 - Mandatory Test 6.1.27.14
 - Mandatory Test 6.1.27.15
@@ -422,6 +421,7 @@ export const mandatoryTest_6_1_27_8: DocumentTest
 export const mandatoryTest_6_1_27_9: DocumentTest
 export const mandatoryTest_6_1_27_10: DocumentTest
 export const mandatoryTest_6_1_27_11: DocumentTest
+export const mandatoryTest_6_1_27_12: DocumentTest
 export const mandatoryTest_6_1_28: DocumentTest
 export const mandatoryTest_6_1_29: DocumentTest
 export const mandatoryTest_6_1_30: DocumentTest
diff --git a/csaf_2_1/mandatoryTests.js b/csaf_2_1/mandatoryTests.js
index 95c5c092..d31895cc 100644
--- a/csaf_2_1/mandatoryTests.js
+++ b/csaf_2_1/mandatoryTests.js
@@ -38,6 +38,7 @@ export { mandatoryTest_6_1_1 } from './mandatoryTests/mandatoryTest_6_1_1.js'
 export { mandatoryTest_6_1_8 } from './mandatoryTests/mandatoryTest_6_1_8.js'
 export { mandatoryTest_6_1_11 } from './mandatoryTests/mandatoryTest_6_1_11.js'
 export { mandatoryTest_6_1_13 } from './mandatoryTests/mandatoryTest_6_1_13.js'
+export { mandatoryTest_6_1_27_12 } from './mandatoryTests/mandatoryTest_6_1_27_12.js'
 export { mandatoryTest_6_1_34 } from './mandatoryTests/mandatoryTest_6_1_34.js'
 export { mandatoryTest_6_1_35 } from './mandatoryTests/mandatoryTest_6_1_35.js'
 export { mandatoryTest_6_1_9 } from './mandatoryTests/mandatoryTest_6_1_9.js'
diff --git a/csaf_2_1/mandatoryTests/mandatoryTest_6_1_27_12.js b/csaf_2_1/mandatoryTests/mandatoryTest_6_1_27_12.js
new file mode 100644
index 00000000..2ba6c559
--- /dev/null
+++ b/csaf_2_1/mandatoryTests/mandatoryTest_6_1_27_12.js
@@ -0,0 +1,74 @@
+import Ajv from 'ajv/dist/jtd.js'
+
+const ajv = new Ajv()
+
+/*
+  This is the jtd schema that needs to match the input document so that the
+  test is activated. If this schema doesn't match it normally means that the input
+  document does not validate against the csaf json schema or optional fields that
+  the test checks are not present.
+ */
+const inputSchema = /** @type {const} */ ({
+  additionalProperties: true,
+  properties: {
+    document: {
+      additionalProperties: true,
+      properties: {
+        category: {
+          type: 'string',
+        },
+      },
+    },
+    vulnerabilities: {
+      elements: {
+        additionalProperties: true,
+        optionalProperties: {
+          product_status: {
+            additionalProperties: true,
+            optionalProperties: {
+              known_affected: {
+                elements: {
+                  type: 'string',
+                },
+              },
+            },
+          },
+        },
+      },
+    },
+  },
+})
+
+const validate = ajv.compile(inputSchema)
+
+/**
+ * This implements the mandatory test 6.1.27.12 of the CSAF 2.1 standard.
+ *
+ * @param {unknown} doc
+ */
+export function mandatoryTest_6_1_27_12(doc) {
+  /*
+    The `ctx` variable holds the state that is accumulated during the test ran and is
+    finally returned by the function.
+   */
+  const ctx = {
+    errors:
+      /** @type {Array<{ instancePath: string; message: string }>} */ ([]),
+    isValid: true,
+  }
+
+  if (!validate(doc) || doc.document.category !== 'csaf_security_advisory')
+    return ctx
+
+  for (const [index, vulnerability] of doc.vulnerabilities.entries()) {
+    if (!vulnerability.product_status?.known_affected) {
+      ctx.isValid = false
+      ctx.errors.push({
+        instancePath: `/vulnerabilities/${index}/product_status`,
+        message: `missing the know_effected element`,
+      })
+    }
+  }
+
+  return ctx
+}
diff --git a/tests/csaf_2_1/mandatoryTest_6_1_27_12.js b/tests/csaf_2_1/mandatoryTest_6_1_27_12.js
new file mode 100644
index 00000000..0643bc86
--- /dev/null
+++ b/tests/csaf_2_1/mandatoryTest_6_1_27_12.js
@@ -0,0 +1,38 @@
+import assert from 'node:assert/strict'
+import { mandatoryTest_6_1_27_12 } from '../../csaf_2_1/mandatoryTests/mandatoryTest_6_1_27_12.js'
+
+describe('mandatoryTest_6_1_27_12', function () {
+  it('only runs on documents matching the input schema', function () {
+    assert.equal(
+      mandatoryTest_6_1_27_12({
+        document: 'invalid json',
+        vulnerabilities: [
+          {
+            product_status: {
+              under_investigation: ['CSAFPID-9080700'],
+            },
+          },
+        ],
+      }).isValid,
+      true
+    )
+  })
+
+  it('only runs on csaf_security_advisory documents', function () {
+    assert.equal(
+      mandatoryTest_6_1_27_12({
+        document: {
+          category: 'unknown category',
+        },
+        vulnerabilities: [
+          {
+            product_status: {
+              under_investigation: ['CSAFPID-9080700'],
+            },
+          },
+        ],
+      }).isValid,
+      true
+    )
+  })
+})
diff --git a/tests/csaf_2_1/oasis.js b/tests/csaf_2_1/oasis.js
index 6fb44c13..89d12404 100644
--- a/tests/csaf_2_1/oasis.js
+++ b/tests/csaf_2_1/oasis.js
@@ -20,7 +20,6 @@ const excluded = [
   '6.1.27.4',
   '6.1.27.6',
   '6.1.27.11',
-  '6.1.27.12',
   '6.1.27.13',
   '6.1.27.14',
   '6.1.27.15',