Windows 10 CryptoAPI Spoofing Vulnerability
After Adobe today releases its first Patch Tuesday updates for 2020, Microsoft has now also published its January security advisories warning billions of users of 49 new vulnerabilities in its various products.

What's so special about the latest Patch Tuesday is that one of the updates fixes a serious flaw in the core cryptographic component of widely used Windows 10, Server 2016 and 2019 editions that was discovered and reported to the company by the National Security Agency (NSA) of the United States.

What's more interesting is that this is the first security flaw in Windows OS that the NSA reported responsibly to Microsoft, unlike the Eternalblue SMB flaw that the agency kept secret for at least five years and then was leaked to the public by a mysterious group, which caused WannaCry menace in 2017.

CVE-2020-0601: Windows CryptoAPI Spoofing Vulnerability


According to an advisory released by Microsoft, the flaw, dubbed 'NSACrypt' and tracked as CVE-2020-0601, resides in the Crypt32.dll module that contains various 'Certificate and Cryptographic Messaging functions' used by the Windows Crypto API for handling encryption and decryption of data.

The issue resides in the way Crypt32.dll module validates Elliptic Curve Cryptography (ECC) certificates that is currently the industry standard for public-key cryptography and used in the majority of SSL/TLS certificates.

In a press release published by the NSA, the agency explains "the certificate validation vulnerability allows an attacker to undermine how Windows verifies cryptographic trust and can enable remote code execution."

Exploitation of the vulnerability allows attackers to abuse validation of trust between:
  • HTTPS connections
  • Signed files and emails
  • Signed executable code launched as user-mode processes
Though technical details of the flaw are not yet available to the public, Microsoft confirms the flaw, which if exploited successfully, could allow attackers to spoof digital signatures on software, tricking the operating system into installing malicious software while impersonating the identity of any legitimate software—without users' knowledge.

"A spoofing vulnerability exists in the way Windows CryptoAPI (Crypt32.dll) validates Elliptic Curve Cryptography (ECC) certificates," the microsoft advisory says.

"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. The user would have no way of knowing the file was malicious because the digital signature would appear to be from a trusted provider."

Besides this, the flaw in CryptoAPI could also make it easy for remote man-in-the-middle attackers to impersonate websites or decrypt confidential information on user connections to the affected software.

"This vulnerability is classed Important and we have not seen it used in active attacks," the microsoft said in a separate blog post.

"This vulnerability is one example of our partnership with the security research community where a vulnerability was privately disclosed and an update released to ensure customers were not put at risk."

"The consequences of not patching the vulnerability are severe and widespread. Remote exploitation tools will likely be made quickly and widely available," the NSA said.

Besides Windows CryptoAPI spoofing vulnerability that has been rated 'important' in severity, Microsoft has also patched 48 other vulnerabilities, 8 of which are critical and rest all 40 are important.

There is no mitigating or workaround available for this vulnerability, so you're highly recommended to install the latest software updates by heading on to your Windows Settings → Update & Security → Windows Update → clicking 'Check for updates on your PC.'

Other Critical RCE Flaws in Windows


Two of the critical issues affect Windows Remote Desktop Gateway (RD Gateway), tracked as CVE-2020-0609 and CVE-2020-0610, that can be exploited by unauthenticated attackers to execute malicious code on targeted systems just by sending a specially crafted request via RDP.

"This vulnerability is pre-authentication and requires no user interaction. An attacker who successfully exploited this vulnerability could execute arbitrary code on the target system," the advisory says.

One critical issue in Remote Desktop Client, tracked as CVE-2020-0611, could lead to a reverse RDP attack where a malicious server can execute arbitrary code on the computer of the connecting client.ability

"To exploit this vulnerability, an attacker would need to have control of a server and then convince a user to connect to it," the advisory says.

"An attacker could also compromise a legitimate server, host malicious code on it, and wait for the user to connect."

Fortunately, none of the flaws addressed this month by Microsoft were publicly disclosed or found being exploited in the wild.
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