Unofficial Patch Released for New Actively Exploited Windows MotW Vulnerability

An unofficial patch has been built offered for an actively exploited security flaw in Microsoft Windows that tends to make it feasible for documents signed with malformed signatures to sneak past Mark-of-the-Web (MotW) protections.

The take care of, introduced by 0patch, comes weeks immediately after HP Wolf Security disclosed a Magniber ransomware marketing campaign that targets users with pretend security updates which utilize a JavaScript file to proliferate the file-encrypting malware.

Though files downloaded from the internet in Windows are tagged with a MotW flag to protect against unauthorized actions, it has given that been located that corrupt Authenticode signatures can be employed to enable the execution of arbitrary executables devoid of any SmartScreen warning.

Authenticode is a Microsoft code-signing technology that authenticates the identification of the publisher of a individual piece of software and verifies whether the application was tampered with soon after it was signed and posted.

“The [JavaScript] file in fact has the MotW but continue to executes without the need of a warning when opened,” HP Wolf Security researcher Patrick Schläpfer noted.

Source: Will Dormann Twitter

“If the file has this malformed Authenticode signature, the SmartScreen and/or file-open up warning dialog will be skipped,” security researcher Will Dormann described.

Now in accordance to 0patch co-founder Mitja Kolsek, the zero-working day bug is the final result of SmartScreen returning an exception when parsing the malformed signature, which is improperly interpreted as a decision to operate the plan fairly than trigger a warning.

Fixes for the flaw also appear fewer than two weeks after unofficial patches have been shipped for a further zero-day MotW bypass flaw that arrived to mild in July and has due to the fact occur beneath active attack, per security researcher Kevin Beaumont.

The vulnerability, uncovered by Dormann, relates to how Windows fails to set the MotW identifier to documents extracted from especially crafted .ZIP information.

“Attackers thus understandably favor their destructive data files not remaining marked with MOTW this vulnerability enables them to generate a ZIP archive this kind of that extracted malicious data files will not be marked,” Kolsek claimed.

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Some parts of this article are sourced from:
thehackernews.com