diff --git a/README.md b/README.md
index 1c1f5999..292940eb 100644
--- a/README.md
+++ b/README.md
@@ -433,6 +433,7 @@ export const mandatoryTest_6_1_41: DocumentTest
 export const mandatoryTest_6_1_43: DocumentTest
 export const mandatoryTest_6_1_45: DocumentTest
 export const mandatoryTest_6_1_52: DocumentTest
+export const mandatoryTest_6_1_56: DocumentTest
 ```
 
 [(back to top)](#bsi-csaf-validator-lib)
diff --git a/csaf_2_1/mandatoryTests.js b/csaf_2_1/mandatoryTests.js
index 482f0616..dde8f5f7 100644
--- a/csaf_2_1/mandatoryTests.js
+++ b/csaf_2_1/mandatoryTests.js
@@ -61,3 +61,4 @@ export { mandatoryTest_6_1_41 } from './mandatoryTests/mandatoryTest_6_1_41.js'
 export { mandatoryTest_6_1_43 } from './mandatoryTests/mandatoryTest_6_1_43.js'
 export { mandatoryTest_6_1_45 } from './mandatoryTests/mandatoryTest_6_1_45.js'
 export { mandatoryTest_6_1_52 } from './mandatoryTests/mandatoryTest_6_1_52.js'
+export { mandatoryTest_6_1_56 } from './mandatoryTests/mandatoryTest_6_1_56.js'
diff --git a/csaf_2_1/mandatoryTests/mandatoryTest_6_1_56.js b/csaf_2_1/mandatoryTests/mandatoryTest_6_1_56.js
new file mode 100644
index 00000000..23753b61
--- /dev/null
+++ b/csaf_2_1/mandatoryTests/mandatoryTest_6_1_56.js
@@ -0,0 +1,153 @@
+import Ajv from 'ajv/dist/jtd.js'
+
+/** @typedef {string} Product
+
+/** @typedef {import('ajv/dist/jtd.js').JTDDataType<typeof inputSchema>} InputSchema */
+
+/** @typedef {InputSchema['vulnerabilities'][number]} Vulnerability */
+
+/** @typedef {NonNullable<Vulnerability['metrics']>[number]} Metric */
+
+const jtdAjv = new Ajv()
+
+const inputSchema = /** @type {const} */ ({
+  additionalProperties: true,
+  properties: {
+    vulnerabilities: {
+      elements: {
+        additionalProperties: true,
+        optionalProperties: {
+          metrics: {
+            elements: {
+              additionalProperties: true,
+              optionalProperties: {
+                source: {
+                  type: 'string',
+                },
+                products: {
+                  elements: { type: 'string' },
+                },
+                content: {
+                  additionalProperties: true,
+                  optionalProperties: {
+                    cvss_v2: {
+                      additionalProperties: true,
+                      optionalProperties: {
+                        version: { type: 'string' },
+                      },
+                    },
+                    cvss_v3: {
+                      additionalProperties: true,
+                      optionalProperties: {
+                        version: { type: 'string' },
+                      },
+                    },
+                    cvss_v4: {
+                      additionalProperties: true,
+                      optionalProperties: {
+                        version: { type: 'string' },
+                      },
+                    },
+                    qualitative_severity_rating: {
+                      type: 'string',
+                    },
+                  },
+                },
+              },
+            },
+          },
+        },
+      },
+    },
+  },
+})
+
+const validate = jtdAjv.compile(inputSchema)
+
+/**
+ * For each item in `/vulnerabilities` it MUST be tested that no Qualitative Severity Rating and CVSS values are
+ * listed for the tuple of Product ID and source.
+ * @param {unknown} doc
+ */
+export function mandatoryTest_6_1_56(doc) {
+  const ctx = {
+    errors:
+      /** @type {Array<{ instancePath: string; message: string }>} */ ([]),
+    isValid: true,
+  }
+
+  /** @type {Array<{ message: string; instancePath: string }>} */
+  const errors = []
+
+  if (!validate(doc)) {
+    return ctx
+  }
+
+  /** @type {Array<Vulnerability>} */
+  const vulnerabilities = doc.vulnerabilities
+
+  /**
+   * Create a unique string for the tuple of productId and source
+   * to compare them easily
+   * @param {string} productId
+   * @param {string | undefined} source
+   *
+   * @return string
+   */
+  function createTupleStringForProductAndSource(productId, source) {
+    return JSON.stringify({ productId: productId, source: source ?? '' })
+  }
+
+  /**
+   * check whether the given metric contains a cvss (v2, v3 or v4) content
+   * @param  {Metric}  metric
+   * @returns {boolean}
+   */
+  function hasCvssContent(metric) {
+    return (
+      metric.content?.cvss_v2?.version !== undefined ||
+      metric.content?.cvss_v3?.version !== undefined ||
+      metric.content?.cvss_v4?.version !== undefined
+    )
+  }
+
+  vulnerabilities.forEach((vulnerabilityItem, vulnerabilityIndex) => {
+    /** @type {Map<string,string>} */
+    const productIdServiceTuplesCvss = new Map()
+    /** @type {Map<string,string>} */
+    const productIdServiceTuplesRating = new Map()
+
+    /** @type {Array<Metric> | undefined} */
+    const metrics = vulnerabilityItem.metrics
+    metrics?.forEach((metric, metricIndex) => {
+      /** @type {Array<Product> | undefined} */
+      const productsOfMetric = metric.products
+      productsOfMetric?.forEach((product, productIndex) => {
+        if (hasCvssContent(metric)) {
+          productIdServiceTuplesCvss.set(
+            createTupleStringForProductAndSource(product, metric.source),
+            `/vulnerabilities/${vulnerabilityIndex}/metrics/${metricIndex}/products/${productIndex}`
+          )
+        }
+        if (metric.content?.qualitative_severity_rating) {
+          productIdServiceTuplesRating.set(
+            createTupleStringForProductAndSource(product, metric.source),
+            `/vulnerabilities/${vulnerabilityIndex}/metrics/${metricIndex}/products/${productIndex}`
+          )
+        }
+      })
+    })
+
+    productIdServiceTuplesCvss.forEach((value, key) => {
+      if (productIdServiceTuplesRating.has(key))
+        errors.push({
+          message:
+            'in the metrics of the vulnerability a Qualitative Severity Rating and CVSS value ' +
+            'with the same product id and source is used.',
+          instancePath: value,
+        })
+    })
+  })
+
+  return { errors: errors, isValid: errors.length === 0 }
+}
diff --git a/tests/csaf_2_1/mandatoryTest_6_1_56.js b/tests/csaf_2_1/mandatoryTest_6_1_56.js
new file mode 100644
index 00000000..4072cb02
--- /dev/null
+++ b/tests/csaf_2_1/mandatoryTest_6_1_56.js
@@ -0,0 +1,8 @@
+import assert from 'node:assert/strict'
+import { mandatoryTest_6_1_56 } from '../../csaf_2_1/mandatoryTests/mandatoryTest_6_1_56.js'
+
+describe('mandatoryTest_6_1_56', function () {
+  it('only runs on relevant documents', function () {
+    assert.equal(mandatoryTest_6_1_56({ document: 'mydoc' }).isValid, true)
+  })
+})
diff --git a/tests/csaf_2_1/oasis.js b/tests/csaf_2_1/oasis.js
index dbc5a7b9..fc0a7332 100644
--- a/tests/csaf_2_1/oasis.js
+++ b/tests/csaf_2_1/oasis.js
@@ -30,7 +30,6 @@ const excluded = [
   '6.1.53',
   '6.1.54',
   '6.1.55',
-  '6.1.56',
   '6.2.11',
   '6.2.19',
   '6.2.20',