Category Archives: Security

Recent Activity, Security, Troubleshooting, WED Blog, Windows 10

Using Microsoft Safety Scanner MSERT.exe

April 2, 2021 Ed Tittel 1 Comment

With each Patch Tuesday, MS releases a new version of the Malicious Software Removal Tool (MSRT). Just yesterday, I learned about a similar but different tool named Microsoft Safety Scanner (MSERT.exe). At first, I did a double-take to make sure it wasn’t a typo. It’s not, as the Safety Scanner Docs page attests. (Here are live links to the 32-bit and 64-bit downloads mentioned in the lead-in graphic.) Here, I’ll explore what’s involved in using Microsoft Safety Scanner, aka MSERT.exe.

Explanation Precedes Using Microsoft Safety Scanner

MS explains the tool thusly “a scan tool designed to find and remove malware from Windows computers.” It goes on to says “Simply download it and run a scan to find malware and try to reverse changes made by identified threats.” Like the MSRT, the MS Safety Scanner gets updates and new signatures all the time, so MS recommends that you always download a fresh copy any time you’d like to use it. They also observe that it’s only worth using for 10 days, after which one MUST download a new version.

Here’s how MS describes the MSRT on its download page:

Windows Malicious Software Removal Tool (MSRT) helps keep Windows computers free from prevalent malware. MSRT finds and removes threats and reverses the changes made by these threats. MSRT is generally released monthly as part of Windows Update or as a standalone tool available here for download.

I’ll be darned if I can tell much difference between them. Nor do I see much distinction in third-party coverage. That said, Explorer sees big differences in size between the two, to wit:

Notice that MSERT.exe shows up as itself, while MSRT shows up as KB890830, version 5.87. Because MSRT is released monthly through WU, it apparently keeps the same KB number, but gets a new version number with each release. MSERT is not so readily obliging but does show that information on its Properties/Details page. That’s where I learned that MSERT stands for “Microsoft Support Emergency Response Tool.”

Full name plus file version info readily available here.
[Click image for full-sized view.]

Let’s just say this is another tool from MS you can run at your own discretion to check a Windows PC for malware, and attempt cleanup. All this makes me curious to understand why we have access to not one, but two, such tools. Even the best of third-party explanations/explorations tend to be a bit shaky, like this Tom’s Hardware Forums item. Even my home forums community at TenForums is pretty much mum on differences, to my consternation and regret.

Using Microsoft Safety Scanner

The .exe file is portable and runs from anywhere (including the Downloads folder). The Docs don’t say one should run the program as administrator, but I did so anyway. It presents a EULA to which you must agree before it does its thing. Next you get a welcome/disclosure screen:

Click Next, and you get your choice of scan types (quick, full, or customized).

Then, it scans your “most likely compromised” files under quick scan.

On my production PC, the whole process took about 3:00 and produced the following results.

Nothing to see here folks, please move along. A clean bill of health, in other words.

Upon completion, the log file (named msert.log) shows nothing informative about cleanup or actions taken (probably because it found nothing to clean up). Here’s a NotePad++ view of its contents (click to view full-sized, as it’s a little hard to read in native WordPress resolution):

I’m still not sure if you and I really need this tool or not, but it’s nice to know it’s available on demand should you wish to make a malware scan and clean-up pass over your Windows PC. The whole thing still has me wondering…

Recent Activity, Security, Troubleshooting, WED Blog, Windows 10, Windows OS Musings

Multiple Methods Clear Defender Threat History

March 9, 2021 Ed Tittel Leave a comment

First, an admission. I do occasionally use the CCleaner and the MiniTool Partition Wizard (MTPW) installers. Yes, I know they include “bundleware” elements that Defender flags as “potentially unwanted programs” (PUPs). In fact, until you clear the threat history and exclude that history from future scans, Defender keeps reporting them ad infinitum. Sigh. As I worked my way through a UGetFix.com article yesterday on my Lenovo X390 Yoga I learned multiple methods clear Defender threat history. In fact, when none of the article’s methods worked for me, a spin on one of them did the trick.

[Note] The lead-in graphic for this story shows a Defender warning for a “potentially unwanted application” (PUA) from another bundleware instance. That one comes from the Unlocker program (it’s always been a little dicey, which is why I provide a MajorGeeks download link). Use at your own risk.

Enumerating Multiple Methods Clear Defender Threat History

The UGetFix.com article is entitled “Windows Defender identifies the same threat repeatedly — how to fix?” It works readers through three separate methods:

Delete the Service folder within the following Windows folder:
C:\ProgramData\Microsoft\Windows Defender\Scans\History. This is where Defender keeps its logs and threat history info. There’s an alternate method based on Event Viewer described in the article as well to clear the history log.
Prevent Defender from scanning the history file. This occurs in Manage Settings inside Virus & Threat Protection in Defender, under the Exclusions heading. By excluding the preceding folder specification, you stop Defender from repeating warnings based on its own history files.
Clear Browser Caches: YMMV on this one, depending on the browsers you use. I’ll let you puzzle these efforts out for yourselves, from the help systems built into each browser.

As I said, none of the methods worked for me. What did work, was a variation on Item number 1 above. I was unable to delete the Service folder. It came back as “locked by Windows Defender.” What I was able to do, however, was to navigate within the Service folder and edit the history.log file using NotePad++ to delete its contents. I also found a series of two-digit-numbered folders with various history files inside (named 01, 02 and so forth) that I was able to delete (and did so).

After that maneuver, the annoying multiple repetitions of PUP warnings for the CCleaner (version 5.77) and MTPW (version 12.03) installers disappeared. I used Everything to check my systems and make sure the offending files were no longer present, too. It’s only the installers that include bundleware. Once deleted and flushed, they no longer pose any threat.

Concluding Unscientific Rantlet

It’s weird that Defender triggers PUA/PUP warnings from the contents of its own history file. Even when the files that legitimately trigger an alert on a Windows 10 PC are no longer present, the same alerts still trigger — repeatedly! My plea to the Defender development team is that they automatically exclude the history file from scans by default so as to further insulate users from this small but vexing gotcha.

Recent Activity, Security, WED Blog, Windows 10

Simple Command Craters Windows10 PCs Immediately

January 19, 2021 Ed Tittel Leave a comment

It’s not often you see a warning like the one in the lead-in graphic for this story. Indeed, executing a certain string at the command line will immediately crash a Windows 10 PC and render it unbootable. Before I go into details, I’m concerned that a simple command craters Windows10 PCs immediately. (Windows 8, 8.1, and XP are also reportedly affected, but not Windows 7.) Opportunities for malicious use are mind-boggling.

[Note: the lead-in graphic comes courtesy of Sergey Tkachenko at WinAero,com. He posted the story in which it appears Friday, January 15.]

It gets worse. That same string also corrupts any targeted NTFS volume in a URL (just a portion of that string in the address bar will do it). Furthermore, it works from inside a ZIP archive, an ISO, VHD, or VHDX file, too. I’m stunned!

I actually debated myself for days on whether or not to share this info. I finally concluded that the Windows community needs to know. It might arm bad actors with new ammunition. Hopefully, that danger is offset by the increased care it should cultivate in everyone else who learns about it.

What Simple Command Craters Windows10 PCs Immediately?

The command can occur in a file reference at the command line or in PowerShell. The simplest invocation is:

cd c:\:$i30:$bitmap

That’s it. Doesn’t look like much, does it? It can address other drive letters (in which case, it will corrupt them instead). C: is particularly dangerous because it’s the default volume where Windows and all of its necessary pieces and parts reside. Once the string is entered, an error message appears. It informs you that “The file or directory is corrupted and unreadable.” Windows will attempt repairs via Chkdsk upon restart, but it will not succeed.

According to Tkachenko:

…users have figured that it is enough to paste the above ‘:$i30’ string into the browser address bar.

to crater the C: drive. Not good!

Holy Moly! How does THIS work?

This exploit is based on the NTFS $i30 index attribute, which ties into filesystem directories and contains a list of its files and subfolders, and may include deleted items as well as active ones. If you search on “$i30 index attribute” or “NTFS $i30 attribute” you’ll see it’s well-known to computer forensics professionals. It’s also a critical part of the MFT (Master File Table) structures for NTFS. Nobody yet knows or understands why referencing it in a command, URL, or archived file structure is damaging.

According to Tkachenko, the security researcher who found this gotcha says:

I have no idea why it corrupts stuff and it would be a lot of work to find out because the reg key that should BSOD on corruption does not work. So, I’ll leave it to the people with the source code…

MS knows about this now and is reportedly working on a fix. This one should be a doozy, and should get fixed as quickly as they can manage it. In the meantime, watch out!

Do NOT try this at home (or at work, or anywhere else, either). If you simply have to try it, do it in a throwaway VM. Otherwise, cleanup will take time and effort, even if it’s just to restore a backup. As the man said “You have been warned.”