Security Experts:

Out-of-Band Windows Updates Patch Wormable SMB Vulnerability

Microsoft has released out-of-band updates for Windows to patch a critical remote code execution vulnerability in Server Message Block 3.0 (SMBv3) that has been described as “wormable.”

The vulnerability, related to the way SMB 3.1.1 handles certain requests, can be exploited by an unauthenticated attacker to execute arbitrary code on SMB servers and clients.

In attacks aimed at SMB servers, the attacker needs to send specially crafted packets to the targeted system, and in the case of clients, the hacker has to convince the victim to connect to a malicious SMBv3 server.

The existence of the vulnerability was disclosed by Microsoft on Tuesday, when the company released its monthly security updates. At the time, Microsoft said it had been working on a patch and provided mitigation advice.

The flaw, discovered by Microsoft’s own researchers, is officially tracked as CVE-2020-0796 and some members of the cybersecurity industry have named it CoronaBlue and SMBGhost. The weakness impacts Windows 10 and Windows Server versions 1903 and 1909.

Microsoft has not disclosed too many technical details about the vulnerability and a patch was not available until now for analysis. However, researchers have still managed to create scanners for detecting vulnerable servers, and Kryptos Logic claims its experts developed a proof-of-concept (PoC) exploit that achieves a DoS condition.

Kryptos Logic says it has conducted an internet-wide scan for CVE-2020-0796 and identified roughly 48,000 vulnerable hosts.

Users who are unable to immediately apply the patch have been advised to disable SMBv3 compression by following the instructions provided by Microsoft.

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Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.