From 8564f9d963da8d82a77612d4ade12e36962c594c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Andr=C3=A9=20Kallehauge?=
 <3846700+kallehauge@users.noreply.github.com>
Date: Mon, 12 Oct 2026 14:07:03 +0200
Subject: [PATCH 1/3] fix(dk/cvr): reject numbers that start with 0

No CVR number starts with 0, and python-stdnum's dk/cvr refuses them
with InvalidFormat. Without the check, 00000000 passes as a valid CVR
because its modulus 11 sum is 0, so a common placeholder value is
accepted as a real company number.
---
 src/dk/cvr.spec.ts | 10 +++++++++-
 src/dk/cvr.ts      |  2 +-
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/src/dk/cvr.spec.ts b/src/dk/cvr.spec.ts
index 541bcd62..43638f6b 100644
--- a/src/dk/cvr.spec.ts
+++ b/src/dk/cvr.spec.ts
@@ -1,5 +1,5 @@
 import { validate, format } from './cvr';
-import { InvalidLength, InvalidChecksum } from '../exceptions';
+import { InvalidLength, InvalidChecksum, InvalidFormat } from '../exceptions';
 
 describe('dk/cvr', () => {
   it('format:DK 13585628', () => {
@@ -31,4 +31,12 @@ describe('dk/cvr', () => {
 
     expect(result.error).toBeInstanceOf(InvalidChecksum);
   });
+
+  // No CVR number starts with 0. These all pass the modulus 11 check, so the
+  // leading digit is the only thing that rejects them.
+  test.each(['00000000', 'DK00000000', '01000004'])('validate:%s', value => {
+    const result = validate(value);
+
+    expect(result.error).toBeInstanceOf(InvalidFormat);
+  });
 });
diff --git a/src/dk/cvr.ts b/src/dk/cvr.ts
index b8e69ca2..cfbe064d 100644
--- a/src/dk/cvr.ts
+++ b/src/dk/cvr.ts
@@ -54,7 +54,7 @@ const impl: Validator = {
     if (value.length !== 8) {
       return { isValid: false, error: new exceptions.InvalidLength() };
     }
-    if (!strings.isdigits(value)) {
+    if (!strings.isdigits(value) || value[0] === '0') {
       return { isValid: false, error: new exceptions.InvalidFormat() };
     }
 

From 8e94d1b41d81299259ea9273e034742e718caec5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Andr=C3=A9=20Kallehauge?=
 <3846700+kallehauge@users.noreply.github.com>
Date: Mon, 12 Oct 2026 14:22:54 +0200
Subject: [PATCH 2/3] test(dk/cvr): a real company's CVR still passes

Novo Nordisk A/S (24256790), active in the Danish CVR register, with
and without the DK prefix.
---
 src/dk/cvr.spec.ts | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/dk/cvr.spec.ts b/src/dk/cvr.spec.ts
index 43638f6b..036c8477 100644
--- a/src/dk/cvr.spec.ts
+++ b/src/dk/cvr.spec.ts
@@ -39,4 +39,11 @@ describe('dk/cvr', () => {
 
     expect(result.error).toBeInstanceOf(InvalidFormat);
   });
+
+  // Novo Nordisk A/S, active in the Danish CVR register: real numbers still pass.
+  test.each(['24256790', 'DK24256790'])('validate:%s', value => {
+    const result = validate(value);
+
+    expect(result.isValid && result.compact).toEqual('24256790');
+  });
 });

From dd809555a158e479ac7377323cf2735cd1a150c9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Andr=C3=A9=20Kallehauge?=
 <3846700+kallehauge@users.noreply.github.com>
Date: Mon, 12 Oct 2026 14:24:06 +0200
Subject: [PATCH 3/3] test(dk/cvr): describe the registered number by its rule,
 not its owner

---
 src/dk/cvr.spec.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/dk/cvr.spec.ts b/src/dk/cvr.spec.ts
index 036c8477..a20e519c 100644
--- a/src/dk/cvr.spec.ts
+++ b/src/dk/cvr.spec.ts
@@ -40,7 +40,7 @@ describe('dk/cvr', () => {
     expect(result.error).toBeInstanceOf(InvalidFormat);
   });
 
-  // Novo Nordisk A/S, active in the Danish CVR register: real numbers still pass.
+  // A registered CVR number still passes.
   test.each(['24256790', 'DK24256790'])('validate:%s', value => {
     const result = validate(value);