diff --git a/csaf_2_1/mandatoryTests.js b/csaf_2_1/mandatoryTests.js
index 8ae82bc4..0a1ed735 100644
--- a/csaf_2_1/mandatoryTests.js
+++ b/csaf_2_1/mandatoryTests.js
@@ -1,5 +1,4 @@
 export {
-  mandatoryTest_6_1_2,
   mandatoryTest_6_1_3,
   mandatoryTest_6_1_4,
   mandatoryTest_6_1_5,
@@ -35,6 +34,7 @@ export {
   mandatoryTest_6_1_33,
 } from '../mandatoryTests.js'
 export { mandatoryTest_6_1_1 } from './mandatoryTests/mandatoryTest_6_1_1.js'
+export { mandatoryTest_6_1_2 } from './mandatoryTests/mandatoryTest_6_1_2.js'
 export { mandatoryTest_6_1_6 } from './mandatoryTests/mandatoryTest_6_1_6.js'
 export { mandatoryTest_6_1_7 } from './mandatoryTests/mandatoryTest_6_1_7.js'
 export { mandatoryTest_6_1_8 } from './mandatoryTests/mandatoryTest_6_1_8.js'
diff --git a/csaf_2_1/mandatoryTests/mandatoryTest_6_1_2.js b/csaf_2_1/mandatoryTests/mandatoryTest_6_1_2.js
new file mode 100644
index 00000000..c6adedb3
--- /dev/null
+++ b/csaf_2_1/mandatoryTests/mandatoryTest_6_1_2.js
@@ -0,0 +1,160 @@
+import Ajv from 'ajv/dist/jtd.js'
+
+const ajv = new Ajv()
+
+const branchSchema = /** @type {const} */ ({
+  additionalProperties: true,
+  optionalProperties: {
+    branches: {
+      elements: {
+        additionalProperties: true,
+        properties: {},
+      },
+    },
+    product: {
+      additionalProperties: true,
+      optionalProperties: {
+        product_id: { type: 'string' },
+      },
+    },
+  },
+})
+
+const validateBranch = ajv.compile(branchSchema)
+
+const fullProductNameSchema = /** @type {const} */ ({
+  additionalProperties: true,
+  optionalProperties: {
+    product_id: { type: 'string' },
+  },
+})
+
+/*
+  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,
+  optionalProperties: {
+    product_tree: {
+      additionalProperties: true,
+      optionalProperties: {
+        branches: {
+          elements: branchSchema,
+        },
+        full_product_names: {
+          elements: fullProductNameSchema,
+        },
+        product_paths: {
+          elements: {
+            additionalProperties: true,
+            optionalProperties: {
+              full_product_name: fullProductNameSchema,
+            },
+          },
+        },
+      },
+    },
+  },
+})
+
+const validate = ajv.compile(inputSchema)
+
+/**
+ * @typedef {import('ajv/dist/core').JTDDataType<typeof branchSchema>} Branch
+ * @typedef {import('ajv/dist/core').JTDDataType<typeof fullProductNameSchema>} FullProductName
+ */
+
+/**
+ * This implements the mandatory test 6.1.2 of the CSAF 2.1 standard.
+ *
+ * @param {unknown} doc
+ */
+export function mandatoryTest_6_1_2(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)) {
+    return ctx
+  }
+
+  /** @type {Map<string, string>} */
+  const seenProductIds = new Map()
+
+  doc.product_tree?.branches?.forEach((branch, index) => {
+    checkBranch(`/product_tree/branches/${index}`, branch)
+  })
+
+  doc.product_tree?.full_product_names?.forEach((fullProductName, index) => {
+    checkFullProductName(
+      `/product_tree/full_product_names/${index}`,
+      fullProductName
+    )
+  })
+
+  doc.product_tree?.product_paths?.forEach((productPath, index) => {
+    const fullProductName = productPath.full_product_name
+    if (!fullProductName) return
+    checkFullProductName(
+      `/product_tree/product_paths/${index}/full_product_name`,
+      fullProductName
+    )
+  })
+
+  return ctx
+
+  /**
+   * Checks whether the given product_id was already defined and registers an error if so.
+   *
+   * @param {string} instancePath The instance path of the product_id to check.
+   * @param {string} productId The product_id value to check.
+   */
+  function checkProductId(instancePath, productId) {
+    if (seenProductIds.has(productId)) {
+      ctx.isValid = false
+      ctx.errors.push({
+        instancePath,
+        message: 'duplicate definition of product_id',
+      })
+    } else {
+      seenProductIds.set(productId, instancePath)
+    }
+  }
+
+  /**
+   * Checks the product_id in the given "full product name".
+   *
+   * @param {string} prefix The instance path prefix of the "full product name".
+   * @param {FullProductName} fullProductName The "full product name" object.
+   */
+  function checkFullProductName(prefix, fullProductName) {
+    if (fullProductName.product_id) {
+      checkProductId(`${prefix}/product_id`, fullProductName.product_id)
+    }
+  }
+
+  /**
+   * Checks the product_id in the given branch object and its branch children.
+   *
+   * @param {string} prefix The instance path prefix of the "branch".
+   * @param {Branch} branch The "branch" object.
+   */
+  function checkBranch(prefix, branch) {
+    if (branch.product?.product_id) {
+      checkProductId(`${prefix}/product/product_id`, branch.product.product_id)
+    }
+    branch.branches?.forEach((child, index) => {
+      if (!validateBranch(child)) return
+      checkBranch(`${prefix}/branches/${index}`, child)
+    })
+  }
+}
diff --git a/tests/csaf_2_1/mandatoryTest_6_1_2.js b/tests/csaf_2_1/mandatoryTest_6_1_2.js
new file mode 100644
index 00000000..617de372
--- /dev/null
+++ b/tests/csaf_2_1/mandatoryTest_6_1_2.js
@@ -0,0 +1,65 @@
+import assert from 'node:assert'
+import { mandatoryTest_6_1_2 } from '../../csaf_2_1/mandatoryTests/mandatoryTest_6_1_2.js'
+
+describe('mandatory test 6.1.2', function () {
+  describe('valid examples', function () {
+    it('only runs on relevant documents', function () {
+      assert.equal(mandatoryTest_6_1_2({ product_tree: 'mydoc' }).isValid, true)
+    })
+  })
+  it('skips invalid full product names', function () {
+    assert.equal(
+      mandatoryTest_6_1_2({
+        product_tree: {
+          full_product_names: [
+            {
+              product_id: { invalid: true },
+            },
+          ],
+        },
+      }).isValid,
+      true
+    )
+  })
+
+  it('validates branches and skips invalid ones', function () {
+    assert.equal(
+      mandatoryTest_6_1_2({
+        product_tree: {
+          branches: [
+            {
+              product: {
+                product_id: 'CSAFPID-9080700',
+              },
+              branches: [
+                {
+                  product: 'CSAFPID-9080701',
+                },
+                {
+                  branches: [{}],
+                },
+              ],
+            },
+          ],
+        },
+      }).isValid,
+      true
+    )
+  })
+
+  it('validates product_paths and skips invalid ones', function () {
+    assert.equal(
+      mandatoryTest_6_1_2({
+        product_tree: {
+          product_paths: [
+            {
+              full_product_name: {},
+            },
+            {},
+          ],
+        },
+      }).isValid,
+      true
+    )
+  })
+})