Cropped screenshots on affected software leave behind image data that can be recovered, potentially revealing uncropped screenshot context.
Vulnerability
Google Pixel’s Markup tool (CVE-2023-21036, a.k.a. Acropalypse) was discovered in January 2023 and was patched on March 13, 2023.
Separate but similar vulnerability in Microsoft Snipping Tool and Snip & Sketch discovered on March 21, 2023.
Affected Products
Google Pixel’s Markup Tool (Pixel 3 – Pixel 7 Pro)
Microsoft Snipping Tool on Windows 11, Microsoft Snip & Sketch on Windows 10 [8]
Remediation
Google Pixel Markup Tool – March 2023 Android Security Update [1]. It should be noted that any picture cropped by the unpatched Markup tool in the last 5 years was vulnerable. This patch does not retroactively go through old photos to fix the issue. However, 3rd party tools are available to identify and sanitize vulnerable images [2][3].
Windows Snipping Tool – Microsoft is actively testing a patched version of the Windows 11 software and has made a version available to Windows Insiders in the Canary channel (early release & testing builds) in the Microsoft Store as of March 23 [7]. It is anticipated that a formal patch will be released in the near future.
Background
Acropalypse (CVE-2023-21036) – The Acropalypse bug was initially reported to Google in January 2023 and was fixed in the monthly security update released on March 13, 2023. The vulnerability stems from the fact that when an image is cropped using the Markup tool, all of the data from the original image is not deleted and simply resides at the tail of the file [4].
There are two parts for this vulnerability to work. The first part is that the PNG image needs to be compressed in a certain way [5]. The second part is that the original file must be larger than the cropped image that is saved over it. As shown in the visual below, this is because the original image’s size is not updated, and the newly saved image only overwrites a part of that file.
Fig. 1 – Visual representation of PNG data from 9to5Google [4]
Using proof-of-concept code such as the Acropalypse app website [3], vulnerable images can be uploaded, and any retrievable data from the original image file can be recovered.
After the Acropalypse vulnerability became public, security researchers began looking to see if other software behaved in a similar way. On March 21, David Buchanan tweeted his discovery [6] that the Windows 11 Snipping Tool is also vulnerable. While this and the Acropalypse bug are separate vulnerabilities, the idea behind the issue is generally the same. Using this software, any image that is saved, cropped, and then saved again (over the original image) is vulnerable.
PacketWatch has recommendations and best practices to mitigate potentially sensitive data exposure:
Ensure Pixel devices are fully up-to-date with the latest security patch.
Ensure systems and software receive regular patching.
Conduct a review to determine if these vulnerable tools were used for business processes.
As a best practice, avoid capturing or saving sensitive data in unapproved formats such as an image.
Read our latest Enterprise Threat Intelligence Briefing on the Microsoft Outlook Elevation of Privilege Vulnerability, compiled by Kyle Nordby and John Garner.
Vulnerability
CVE-2023-23397 – Microsoft Outlook Elevation of Privilege Vulnerability[1]
Affected Products
All supported versions of Microsoft Outlook for Windows
Remediation
March 14th security patches for Microsoft Outlook[1]
Microsoft released a patch in February regarding a vulnerability with a CVSS score of 9.8, just shy of the maximum of 10. This low-complexity exploit was found and reported to Microsoft by the Ukrainian Computer Emergency Response Team (CERT).
While the Microsoft Security Response Center (MSRC) page[1] states that there is no currently released proof-of-concept (POC) code, security researchers have already figured out how to leverage this exploit. For example, in an article by MDSec on the same day as the announcement[4], a red teamer built a full POC detailing how the exploit works.
This was originally seen being leveraged by Russian threat actors as early as April 2022. With the publicity of the CVE and ease of exploitation, PacketWatch has high confidence that this will be actively exploited in the coming weeks. PacketWatch already monitors for indicators of compromise (IOCs) by checking for suspicious outbound SMB traffic and is currently advising to both patch Outlook and review firewall policies for current clients.
In emails with tasks or calendar events that have due dates, the sender can specify when it becomes overdue, playing a default or custom sound. The exploit itself relies on that property, where the attacker instead replaces the reminder sound with a malicious UNC path[5]. This triggers the Outlook client to send NTLM hashes over SMB to a destination controlled by the attacker. Once completed, the attacker can then leverage those credentials using an NTLM Relay attack, also known as a Pass-the-Hash attack[6].
A patch for affected Outlook clients is already available by Microsoft[1]. Proactively, PacketWatch recommends reviewing what protocols and ports can communicate externally to the environment. Microsoft has also released a detection script that can reveal previous exploitation attempts[3].
THREAT ACTORS LEVERAGING EXPLOITS SEEN IN WILD SINCE DECEMBER
CVE-2021-39144 – VMware Cloud Foundation XStream Remote Code Execution Vulnerability
The Cybersecurity and Infrastructure Security Agency (CISA) has added another VMware vulnerability (CVE-2021-39144) to their growing list of vulnerabilities that they have observed threat actors exploiting in the wild. Exploitation only requires network access to the NSX-v Manager appliance, and successful exploitation will give root privileges (full control) of the NSX-v Manager. This exploit is lower complexity with available POC code, and vulnerable systems only need to be network accessible to any compromised machines, or web accessible, with no additional requirements such as valid credentials.
All versions of VMware NSX Data Center for vSphere (NSX-v) Manager 6.4.14 are affected by the vulnerability. Because these are observed being actively exploited, it is important to ensure that relevant VMware products are fully patched. Additional information is available in the VMware article linked below. Proof of concept (POC) code is currently available, giving both security professionals and threat actors easy methods to find vulnerable systems. The NIST link below has references to available exploit code.
Mitigation
If leveraging VMware Cloud Foundation, ensure that it is fully patched.
Proper documentation of critical and sensitive infrastructure products to quickly identify potentially vulnerable systems.
Network segmentation and limited accessibility to VMware/critical infrastructure should be enforced and periodically reviewed.
The information provided in this article is provided “as-is”. It is not finally evaluated intelligence and should be considered raw information that is provided for strictly situational awareness, given what is known at this time.
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