Microsoft Gets a Patch Tuesday Assist from...the NSA

For its first Patch Tuesday release of the year, Microsoft included a patch for a vulnerability affecting the latest versions of Windows that was discovered and reported to Microsoft by the U.S. National Security Agency.

The NSA's public cooperation with Microsoft in defending users of the operating system marks a change from the agency's well-documented past practice of quietly collecting and weaponizing serious OS flaws that are discovered by its researchers.

Microsoft and the NSA offered differing characterizations of the flaw in Windows 10, Windows Server 2016 and Windows Server 2019. While Microsoft encouraged all users to rapidly apply the patch, the structure of Microsoft's extensive vulnerability rating system slightly underplays the severity of the flaw. The NSA, on the other hand, warned that the consequences of not patching would be "severe and widespread."

The U.S. Cybersecurity and Infrastructure Security Agency (CISA) also released an Emergency Directive and Activity Alert regarding the flaw on Tuesday. While CISA's directive only applies to certain federal agencies, the agency's warnings are often heeded by state and local governments and private sector organizations.

In a Cybersecurity Advisory released at the same time as Microsoft's patches, the NSA said:

NSA has discovered a critical vulnerability (CVE-2020-0601) affecting Microsoft Windows cryptographic functionality. The certificate validation vulnerability allows an attacker to undermine how Windows verifies cryptographic trust and can enable remote code execution. The vulnerability affects Windows 10 and Windows Server 2016/2019 as well as applications that rely on Windows for trust functionality. Exploitation of the vulnerability allows attackers to defeat trusted network connections and deliver executable code while appearing as legitimately trusted entities.

Offering examples of ways that validations of trust may be impacted, the NSA cited HTTPS connections, signed files and e-mails, and signed executable code launched as user-mode processes.

"The vulnerability places Windows endpoints at risk to a broad range of exploitation vectors," the NSA statement said in explaining the agency's alarm over the issue. "NSA assesses the vulnerability to be severe and that sophisticated cyber actors will understand the underlying flaw very quickly and, if exploited, would render the previously mentioned platforms as fundamentally vulnerable. The consequences of not patching the vulnerability are severe and widespread. Remote exploitation tools will likely be made quickly and widely available. Rapid adoption of the patch is the only known mitigation at this time and should be the primary focus for all network owners."

On Microsoft's severity scale, however, the vulnerability was rated as being "important" rather than Microsoft's top level of "critical." Microsoft noted that the flaw had not been publicly disclosed, and there were no known public exploits of the flaw currently. Microsoft did give the flaw its "exploitation more likely" rating for both its latest software releases and older software releases. That is the highest level on Microsoft's exploitability index assessment short of flaws for which exploits already exist. Microsoft applies that rating in cases where Microsoft believes exploit code could be created to consistently exploit the vulnerability and when there are past cases where the specific type of vulnerability has been exploited.

Microsoft's technical description of the vulnerability acknowledges the NSA, which is a first. In a separate public statement about CVE-2020-0601, Mechele Gruhn, principal security program manager for the Microsoft Security Research Center, does not name the NSA but does talk about cooperation with security researchers to work on patching newly discovered vulnerabilities.

"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," Gruhn wrote.

Rumblings that a major patch was on the way emerged earlier in the week. The Krebs on Security blog posted an article on Monday with details of the patch collected from sources, and referenced Twitter posts from security industry insiders who indicated something substantial was afoot.

The agency's cooperation reflects a larger debate about the appropriate role of America's digital spy agency. Historically, the organization is known for its offensive capabilities, hiring top researchers to find and exploit vulnerabilities, build them into sophisticated toolsets, and keep those tools secret and productive for as many years as possible. But the recent security/intelligence/public relations disasters involving the EternalBlue tools released by the Shadow Brokers group highlighted a huge self-defeating flaw in the approach. Namely that with the United States being one of the most digitized and Internet-connected countries in the world, when those U.S.-developed tools get into the hands of adversaries of the United States and U.S. businesses, they can do more damage to the U.S. than they could do to their intended targets.

In a statement reported by The Washington Post, a senior NSA official acknowledged the shift in gears represented by the public cooperation on protecting infrastructure versus secretly attacking it.

"This is...a change in approach...by NSA of working to share, working to lean forward, and then working to really share the data as part of building trust," the Post quoted Anne Neuberger, director of the NSA's Cybersecurity Directorate, as saying Tuesday. Krebs on Security's Brian Krebs, apparently reporting from the same NSA news conference, added via Twitter that Neuberger also said this wasn't the first time NSA has reported a vulnerability to Microsoft, but it is the first time it has accepted credit or attribution when Microsoft asked.

The NSA dubs the operation "Turn a New Leaf," and it received praise from security researchers. That said, the agency's strategic mission of exploiting enemy networks undoubtedly remains unchanged.

Yes, the NSA has just helped Microsoft and its more attentive customers patch a flaw. At the same time, is it tinfoil hat territory to bet that other teams at NSA are involved in the race to develop exploits based on the same vulnerabilities, or perhaps have already done so given the agency's head start?

What we have here is a complicated dance. The NSA is playing a slightly more transparent -- and from the standpoint of software vendors and their customers, a more constructive -- role in network security than it has in the past. At least it is playing that role in this specific case. We'll take what we can get.

Posted by Scott Bekker on 01/14/2020 at 9:13 AM