Microsoft Corp. today pushed software updates to plug more than 70 security holes in its Windows operating systems and related products, including two zero-day vulnerabilities that are already being exploited in active attacks.
Top of the heap on this Fat Patch Tuesday is CVE-2024-21412, a “security feature bypass” in the way Windows handles Internet Shortcut Files that Microsoft says is being targeted in active exploits. Redmond’s advisory for this bug says an attacker would need to convince or trick a user into opening a malicious shortcut file.
Researchers at Trend Micro have tied the ongoing exploitation of CVE-2024-21412 to an advanced persistent threat group dubbed “Water Hydra,” which they say has being using the vulnerability to execute a malicious Microsoft Installer File (.msi) that in turn unloads a remote access trojan (RAT) onto infected Windows systems.
The other zero-day flaw is CVE-2024-21351, another security feature bypass — this one in the built-in Windows SmartScreen component that tries to screen out potentially malicious files downloaded from the Web. Kevin Breen at Immersive Labs says it’s important to note that this vulnerability alone is not enough for an attacker to compromise a user’s workstation, and instead would likely be used in conjunction with something like a spear phishing attack that delivers a malicious file.
Satnam Narang, senior staff research engineer at Tenable, said this is the fifth vulnerability in Windows SmartScreen patched since 2022 and all five have been exploited in the wild as zero-days. They include CVE-2022-44698 in December 2022, CVE-2023-24880 in March 2023, CVE-2023-32049 in July 2023 and CVE-2023-36025 in November 2023.
Narang called special attention to CVE-2024-21410, an “elevation of privilege” bug in Microsoft Exchange Server that Microsoft says is likely to be exploited by attackers. Attacks on this flaw would lead to the disclosure of NTLM hashes, which could be leveraged as part of an NTLM relay or “pass the hash” attack, which lets an attacker masquerade as a legitimate user without ever having to log in.
“We know that flaws that can disclose sensitive information like NTLM hashes are very valuable to attackers,” Narang said. “A Russian-based threat actor leveraged a similar vulnerability to carry out attacks – CVE-2023-23397 is an Elevation of Privilege vulnerability in Microsoft Outlook patched in March 2023.”
Microsoft notes that prior to its Exchange Server 2019 Cumulative Update 14 (CU14), a security feature called Extended Protection for Authentication (EPA), which provides NTLM credential relay protections, was not enabled by default.
“Going forward, CU14 enables this by default on Exchange servers, which is why it is important to upgrade,” Narang said.
Rapid7’s lead software engineer Adam Barnett highlighted CVE-2024-21413, a critical remote code execution bug in Microsoft Office that could be exploited just by viewing a specially-crafted message in the Outlook Preview pane.
“Microsoft Office typically shields users from a variety of attacks by opening files with Mark of the Web in Protected View, which means Office will render the document without fetching potentially malicious external resources,” Barnett said. “CVE-2024-21413 is a critical RCE vulnerability in Office which allows an attacker to cause a file to open in editing mode as though the user had agreed to trust the file.”
Barnett stressed that administrators responsible for Office 2016 installations who apply patches outside of Microsoft Update should note the advisory lists no fewer than five separate patches which must be installed to achieve remediation of CVE-2024-21413; individual update knowledge base (KB) articles further note that partially-patched Office installations will be blocked from starting until the correct combination of patches has been installed.
It’s a good idea for Windows end-users to stay current with security updates from Microsoft, which can quickly pile up otherwise. That doesn’t mean you have to install them on Patch Tuesday. Indeed, waiting a day or three before updating is a sane response, given that sometimes updates go awry and usually within a few days Microsoft has fixed any issues with its patches. It’s also smart to back up your data and/or image your Windows drive before applying new updates.
For a more detailed breakdown of the individual flaws addressed by Microsoft today, check out the SANS Internet Storm Center’s list. For those admins responsible for maintaining larger Windows environments, it often pays to keep an eye on Askwoody.com, which frequently points out when specific Microsoft updates are creating problems for a number of users.
The final Patch Tuesday of 2023 is upon us, with Microsoft Corp. today releasing fixes for a relatively small number of security holes in its Windows operating systems and other software. Even more unusual, there are no known “zero-day” threats targeting any of the vulnerabilities in December’s patch batch. Still, four of the updates pushed out today address “critical” vulnerabilities that Microsoft says can be exploited by malware or malcontents to seize complete control over a vulnerable Windows device with little or no help from users.
Among the critical bugs quashed this month is CVE-2023-35628, a weakness present in Windows 10 and later versions, as well as Microsoft Server 2008 and later. Kevin Breen, senior director of threat research at Immersive Labs, said the flaw affects MSHTML, a core component of Windows that is used to render browser-based content. Breen notes that MSHTML also can be found in a number of Microsoft applications, including Office, Outlook, Skype and Teams.
“In the worst-case scenario, Microsoft suggests that simply receiving an email would be enough to trigger the vulnerability and give an attacker code execution on the target machine without any user interaction like opening or interacting with the contents,” Breen said.
Another critical flaw that probably deserves priority patching is CVE-2023-35641, a remote code execution weakness in a built-in Windows feature called the Internet Connection Sharing (ICS) service that lets multiple devices share an Internet connection. While CVE-2023-35641 earned a high vulnerability severity score (a CVSS rating of 8.8), the threat from this flaw may be limited somewhat because an attacker would need to be on the same network as the target. Also, while ICS is present in all versions of Windows since Windows 7, it is not on by default (although some applications may turn it on).
Satnam Narang, senior staff research engineer at Tenable, notes that a number of the non-critical patches released today were identified by Microsoft as “more likely to be exploited.” For example, CVE-2023-35636, which Microsoft says is an information disclosure vulnerability in Outlook. An attacker could exploit this flaw by convincing a potential victim to open a specially crafted file delivered via email or hosted on a malicious website.
Narang said what makes this one stand out is that exploitation of this flaw would lead to the disclosure of NTLM hashes, which could be leveraged as part of an NTLM relay or “pass the hash” attack, which lets an attacker masquerade as a legitimate user without ever having to log in.
”It is reminiscent of CVE-2023-23397, an elevation of privilege vulnerability in Microsoft Outlook that was exploited in the wild as a zero day and patched in the March 2023 Patch Tuesday release,” Narang said. “However, unlike CVE-2023-23397, CVE-2023-35636 is not exploitable via Microsoft’s Preview Pane, which lowers the severity of this flaw.”
As usual, the SANS Internet Storm Center has a good roundup on all of the patches released today and indexed by severity. Windows users, please consider backing up your data and/or imaging your system before applying any updates. And feel free to sound off in the comments if you experience any difficulties as a result of these patches.
Microsoft today released updates to fix more than five dozen security holes in its Windows operating systems and related software, including three “zero day” vulnerabilities that Microsoft warns are already being exploited in active attacks.
The zero-day threats targeting Microsoft this month include CVE-2023-36025, a weakness that allows malicious content to bypass the Windows SmartScreen Security feature. SmartScreen is a built-in Windows component that tries to detect and block malicious websites and files. Microsoft’s security advisory for this flaw says attackers could exploit it by getting a Windows user to click on a booby-trapped link to a shortcut file.
Kevin Breen, senior director of threat research at Immersive Labs, said emails with .url attachments or logs with processes spawning from .url files “should be a high priority for threat hunters given the active exploitation of this vulnerability in the wild.”
The second zero day this month is CVE-2023-36033, which is a vulnerability in the “DWM Core Library” in Microsoft Windows that was exploited in the wild as a zero day and publicly disclosed prior to patches being available. It affects Microsoft Windows 10 and later, as well as Microsoft Windows Server 2019 and subsequent versions.
“This vulnerability can be exploited locally, with low complexity and without needing high-level privileges or user interaction,” said Mike Walters, president and co-founder of the security firm Action1. “Attackers exploiting this flaw could gain SYSTEM privileges, making it an efficient method for escalating privileges, especially after initial access through methods like phishing.”
The final zero day in this month’s Patch Tuesday is a problem in the “Windows Cloud Files Mini Filter Driver” tracked as CVE-2023-36036 that affects Windows 10 and later, as well as Windows Server 2008 at later. Microsoft says it is relatively straightforward for attackers to exploit CVE-2023-36036 as a way to elevate their privileges on a compromised PC.
Beyond the zero day flaws, Breen said organizations running Microsoft Exchange Server should prioritize several new Exchange patches, including CVE-2023-36439, which is a bug that would allow attackers to install malicious software on an Exchange server. This weakness technically requires the attacker to be authenticated to the target’s local network, but Breen notes that a pair of phished Exchange credentials will provide that access nicely.
“This is typically achieved through social engineering attacks with spear phishing to gain initial access to a host before searching for other vulnerable internal targets – just because your Exchange Server doesn’t have internet-facing authentication doesn’t mean it’s protected,” Breen said.
Breen said this vulnerability goes hand in hand with three other Exchange bugs that Microsoft designated as “exploitation more likely:” CVE-2023-36050, CVE-2023-36039 and CVE-2023-36035.
Finally, the SANS Internet Storm Center points to two additional bugs patched by Microsoft this month that aren’t yet showing signs of active exploitation but that were made public prior to today and thus deserve prioritization. Those include: CVE-2023-36038, a denial of service vulnerability in ASP.NET Core, with a CVSS score of 8.2; and CVE-2023-36413: A Microsoft Office security feature bypass. Exploiting this vulnerability will bypass the protected mode when opening a file received via the web.
Windows users, please consider backing up your data and/or imaging your system before applying any updates. And feel free to sound off in the comments if you experience any difficulties as a result of these patches.