Windows 7 and Server 2008 R2 users without Extended Security Updates
have just received a micropatch for CVE-2020-1113, a Windows Task Scheduler Security Feature Bypass.
This vulnerability was patched by Microsoft with May 2020 Updates, but
Windows 7 and Server 2008 users without Extended Security Updates
remained vulnerable.
The vulnerability lies in Task Scheduler accepting RPC requests that can
be relayed. An attacker can piggyback on such requests by having some
logged-on user send an SMB request to their computer, and then act as
man-in-the-middle.
Microsoft's patch makes sure the authentication level of the RPC request
received by Task Scheduler is RPC_C_AUTHN_LEVEL_PKT_PRIVACY, which
prevents such piggybacking. Our micropatch does effectively the same,
with just six CPU instructions on 32-bit Windows, and two CPU instructions on 64-bit Windows:
;This patch is inserted right after the RpcServerInqCallAttributesW call. ;The call fills the RPC_CALL_ATTRIBUTES_V2_W structure with data, and at ; address rsp+78h we can find ;the RPC_CALL_ATTRIBUTES_V2_W.AuthenticationLevel value, which describes ;the level of RPC authentication ;used. The range of this variable is form 0x0 to 0x6, where 0x6 is ;authentication with integrity (signature)
cmp dword[rsp+78h], 6 ;Check if the RPC_CALL_ATTRIBUTES_V2_W.AuthenticationLevel ; value is equal to 6 jb PIT_0x3b449 ;If the value is less than 6, jump to the ;"access denied error" block
code_end patchlet_end
And a video of the micropatch in action:
We'd like to thank Sylvain Heiniger (@sploutchy)
for sharing their analysis and POC, which allowed us to create this
micropatch for Windows users without official security updates. We also
encourage security researchers to privately share their analyses with us
for micropatching.
This
micropatch is immediately available to all 0patch users with a PRO
license, and is targeted at Windows 7 and Windows Server 2008 R2 users
without Extended Security Updates. To obtain the micropatch and have it
applied on your
computer(s) along with other micropatches included with a PRO license,
create an account in 0patch Central, install 0patch Agent and register it to your account. Note that no computer restart is needed for installing the agent or applying/un-applying any 0patch micropatch.
To learn more about 0patch, please visit our Help Center.
We have just released a new 0patch Agent. We don't do that very often, for two reasons: (1) we like the software we're using to be stable, to favor reliability over novelty, and to not introduce unnecessary changes - so that's what we try to do for you; and (2) building and thoroughly testing a piece of software that needs to work reliably on multiple platforms is pretty expensive. Because of the latter, we've micropatched two functional bugs in our previous Agent version (see here and here) instead of hastily issuing a new one. Micropatching is vastly superior to the traditional rebuild-test-distribute model when fixing simple bugs (which most security bugs and many functional ones are) as it incurs minimal risk of breaking something outside the patched bits, requires only narrowly-focused testing, and allows for inexpensive and unobtrusive deployment (and revocation, if needed).
Nevertheless, bugs and feature requests have piled up, and our server is evolving too, prompting the agent to learn a couple of new tricks.
What's new in the new 0patch Agent? If you like details, please refer to release notes, but otherwise the main changes are:
Annoying popups in 0patch FREE are now gone and replaced by a summary popup that will tell you how many patches you're missing out on that would be relevant on your computer.
Log is now displayed much faster in 0patch Console.
Pop-ups are no longer shown when any application is in full screen mode.
The above-mentioned functional bugs that we've previously micropatched have now been patched in the code, so there is no need to apply a micropatch to every process anymore.
Failed syncs immediately after system startup (which many of you have noticed, and thankfully reported) have been fixed.
May we remind you that the agent is still very small, just over 4MB on the file system.
We recommend you update your agent to this new version at your earliest convenience. The update process will not require a computer restart.
Locally Managed 0patchAgents
If you're using 0patch locally on your computer, 0patch Agent has already started notifying you about a new version. To update the agent, launch 0patch Console and in the "AGENT VERSION" box, click on "GET LATEST VERSION" and let the update process complete. Note that the console will disappear in the process, and will get re-launched when the new agent version is installed.
Remotely Managed 0patch Agents
If you're managing 0patch Agents in your organization remotely through 0patch Central, your group settings will determine whether/which agents will get updated automatically and which will require a manual action on your part. To make sure all agents are updated, you can open the All Computers group, select all computers, and under ACTIONS, select "Update agent to new version."
Thank you for using 0patch! As always, we'll appreciate your feedback, bug reports, feature requests and musical recommendations at support@0patch.com.
This month's Patch Tuesday included a fix for CVE-2020-1350, a critical memory corruption vulnerability in Windows DNS Server affecting all Windows Server versions from long-unsupported Server 2003 to the latest Server 2019.
After Microsoft's initial announcement and security advisory, the CheckPoint research team published a detailed article about the issue, describing the attack vector and providing enough information for other security researchers to trigger the vulnerability. Just one day later, the first real proof-of-concept was published, developed by Max Van Amerongen (@maxpl0it) from F-Secure Labs, and later several other researchers have shown their own tools triggering the vulnerability.
We can safely assume that offensive teams worldwide are currently trying to develop a reliable arbitrary code execution exploit as they know that Windows Updates take anywhere from long to eternity before getting applied to most Windows Servers out there. Their job will not be trivial, with various exploit mitigations in place on modern Windows servers, but counting on them to fail would be a risky strategy. In addition, many companies are still using Windows Server 2008 machines with no security updates past January this year.
Numerous 0patch customers have one or more Windows 2008 Servers and we wanted to take care of them as quickly as possible. With a working proof-of-concept at hand we could easily create a micropatch for this issue. Let's look at Microsoft's patch first:
The image above shows the difference between vulnerable function SigWireRead (left) and its patched counterpart (right). This function was one of only three functions in dns.exe modified by the July update, and the other two were not relevant for the issue at hand.
Microsoft's patch (gray code blocks) introduced three integer overflow/underflow checks, for one subtraction and two addition operations. When faced with Max's proof-of-concept, it is the third check (the lowest gray code block) that detects the overflow and redirects execution towards function's exit instead of processing the DNS packet further - which would lead to memory corruption.
Our micropatch does logically the same, with one difference - when integer overflow/underflow is detected, it also displays and logs an exploit attempt, allowing admins to know that their server was targeted by an exploit:
code_start push rdi ; push to ensure normal code flow after patch push rax ; push to ensure normal code flow after patch
;First check sub rdi, rax cmp rdi, 0xFFFF ja ExploitBlocked ; the TCP packet is not valid, jump to Exploit Blocked
;Second check movzx eax, byte[rsp+30h+2*8] ; added 2*8 to the original offset to compensate for the 2 pushes at the beginning add ax, 0x14 cmp ax, 0x12 jb ExploitBlocked ; the TCP packet is not valid, jump to Exploit Blocked
;Third check lea ecx, [rax+rdi] cmp cx, ax jb ExploitBlocked ; the TCP packet is not valid, jump to Exploit Blocked jmp End ; the TCP packet is valid, continue with original code ExploitBlocked: pop rax ; restore rax to its previous value pop rdi ; restore rdi to its previous value call PIT_ExploitBlocked ; Exploit Blocked pop up jmp PIT_0x4EC68 ; Exit function, TCP packet not valid End: pop rax ; restore rax to its previous value pop rdi ; restore rdi to its previous value code_end
patchlet_end
We released our micropatch early afternoon CET today and it got applied to all online computers with 0patch PRO worldwide within 60 minutes without restarting the computer or DNS service.
This is how it looks like when a DNS server is attacked without and with 0patch:
The first instance of our micropatch is targeted at Windows Server 2008 R2 without Extended Security Updates, and we plan to port it to Windows Server 2003 next for our users who are for various reasons still using this unsupported server. [Update 7/20/2020: Micropatch is now ported to 32-bit and 64-bit Windows Server 2003.]
Although free official updates exist for all supported Windows servers, admins may not be able to apply them immediately or restart the computer; for such cases, requests for porting our micropatch to specific versions of dns.exe running on affected computers can be sent to sales@0patch.com.
If you have 0patch Agent with PRO license installed on your Windows Server 2008 R2 or Server 2003 computer, our micropatch is already downloaded and applied to your DNS server. Otherwise, to obtain the micropatch and have it
applied on your
computer(s) along with other micropatches included with a PRO license,
create an account in 0patch Central, purchase a PRO license or request a trial at sales@0patch.com, install 0patch Agent and register it to your account.
Note that no computer restart is needed for installing the agent or applying/un-applying any 0patch micropatch.
To learn more about 0patch, please visit our Help Center.
We'd like to thank Max Van Amerongen (@maxpl0it)
from F-Secure Labs for publishing their analysis and POC, and for
providing additional assistance in triggering the vulnerability and
simplifying our test case, thereby allowing us to create this micropatch for
Windows users without official security updates.
Windows 7 and Server 2008 R2 users without Extended Security Updates
have just received a micropatch for CVE-2020-0662, a remote memory corruption vulnerability in DHCP message processing.
This vulnerability was patched by Microsoft with February 2020 Updates, but Windows 7 and Server 2008 users without Extended Security Updates remained vulnerable.
The vulnerability lies in accepting a hardware address in a DHCP packet that is longer than 20h bytes, resulting in out-of-bounds read or write, depending on the Windows version. Our micropatch is logically identical to Microsoft's: it adds a check for the HW address length:
; Added check for Hardware address length, must be <= 20
code_start mov al, [rsi+0xE6] ; [rsi+0xE6] = value of hardware address length cmp al, 0x20 ; compare hardware address length with 0x20 jbe RestoreCodeFlow ; jump if hradware address length is <= 20 call PIT_ExploitBlocked ; exploit blocked shown if hardware address length is > 20 call GetText ; get address for Error text db 'DhcpProcessMessage: ignoring message since HWAdderLength is greater than MAX_HARDWARE_ADDRESS_LENGTH',0 ; Error message GetText: pop rdx ; set rdx to error code address like MS org patch jmp PIT_0x1AB94 ; jump to ensure same code flow like MS patch RestoreCodeFlow: code_end
patchlet_end
We'd like to thank Spencer McIntyre (@zeroSteiner) for sharing their analysis and POC, and for additional assistance in reproducing the bug, which allowed us to create this micropatch for Windows users without official security updates.
This
micropatch is immediately available to all 0patch users with a PRO
license, and is targeted at Windows 7 and Windows Server 2008 R2 users
without Extended Security Updates. To obtain the micropatch and have it
applied on your
computer(s) along with other micropatches included with a PRO license,
create an account in 0patch Central, install 0patch Agent and register it to your account. Note that no computer restart is needed for installing the agent or applying/un-applying any 0patch micropatch.
To learn more about 0patch, please visit our Help Center.
[Update 7/13/2020: Zoom only took one (!) day to issue a new version of Client for Windows that fixes this vulnerability, which is remarkable. We have reviewed their fix and can confirm that it efficiently resolves the vulnerability. With an official vendor fix available to all users, we made our
micropatches for this issue PRO-only according to our guidelines. Meanwhile, after issuing micropatches for this issue targeted at Zoom
Client for Windows versions 5.0.3 to 5.1.2, we noticed a lot of our
users being on all of these versions despite Zoom's highly persistent
update mechanism. We had expected most users to be on version 5.1.2., but this indicates many users may still be on even older Zoom Client
versions. We therefore ported our micropatch to the remaining supported
versions of Zoom Client: 5.0.0., 5.0.1, and 5.0.2. We're now covering
all vulnerable supported clients.]
Earlier this week a security researcher shared a remote code execution "0day" vulnerability in Zoom Client for Windows with our team. The vulnerability allows a remote attacker to execute arbitrary code on victim's computer where Zoom Client for Windows (any currently supported version) is installed by getting the user to perform some typical action such as opening a document file. No security warning is shown to the user in the course of attack.
The researcher (who wants to keep their identity private) stated that they did not report the vulnerability to Zoom either directly or through a broker, but would not object to us reporting it to Zoom.
Analysis
We analyzed the issue and determined it to be only exploitable on Windows 7 and older Windows systems. While Microsoft's official support for Windows 7 has ended this January, there are still millions of home and corporate users out there prolonging its life with Microsoft's Extended Security Updates or with 0patch.
We then documented the issue along with several attack scenarios, and reported it to Zoom earlier today along with a working proof of concept and recommendations for fixing. Should a bug bounty be awarded by Zoom, it shall be waived in favor of a charity of researcher's choice.
Micropatch
On the micropatching side, we were able to quickly create a micropatch that removes the vulnerability in four different places in the code. The micropatch was then ported from the latest version of Zoom Client for Windows (5.1.2) to previous five versions back to 5.0.3 released on May 17, 2020. Zoom Client features a fairly persistent auto-update functionality that is likely to keep home users updated unless they really don't want to be. However, enterprise admins often like to keep control of updates and may stay a couple of versions behind, especially if no security bugs were fixed in the latest versions (which is currently the case).
Our micropatches have already been released and distributed to all online 0patch Agents; Zoom users with 0patch installed are therefore no longer affected by this issue.
According to our guidelines, we're providing these micropatches to everyone for free until Zoom has fixed the issue or made a decision not to fix it. To minimize the risk of exploitation on systems without 0patch, we're not publishing details on this vulnerability until Zoom has fixed the issue, or made a decision not to fix it, or until such details have become public knowledge in any way.
To obtain the free micropatch for this issue and have it applied on your
computer(s),
create a free account in 0patch Central, install 0patch Agent and register it to your account. Note that no computer restart is needed for installing the agent or applying/un-applying any 0patch micropatch.
To learn more about 0patch, please visit our Help Center.
Exploit without and with the micropatch
This video demonstrates how an actual attack could look like, and how 0patch blocks the attack. When 0patch is disabled (or absent), user's clicking on the "Start Video" button triggers the vulnerability and leads to a "HACKED" dialog being shown (of course anything else could be executed instead). With 0patch enabled, the vulnerability is removed from the running Zoom.exe process and clicking on the "Start Video" button does not result in execution of malicious code.
Note that in order to prevent revealing too much information, some prior user activity inside Zoom Client user interface is not shown in the video.
Frequently Asked Questions
Q: Am I affected by this vulnerability if I'm using Windows 10 or Windows 8?
A: No, this vulnerability is only exploitable on Windows 7 and earlier Windows versions. It is likely also exploitable on Windows Server 2008 R2 and earlier though we didn't test that; either way, our micropatch will protect you wherever you're using Zoom Client.
Q: Am I affected by this vulnerability if I'm using Windows 7 fully updated with Extended Security Updates?
A: Yes.
Q: Are other Zoom products affected by this vulnerability too?
A:We did not test any other Zoom products, however only those running on Windows could potentially be affected by this vulnerability.
Q: Is your micropatch for this vulnerability completely free?
A: Yes. If you already have 0patch Agent installed and registered, everything will happen automatically. If not, you only need to create a free account in0patch Central, install 0patch Agent and register it to your account, then all FREE micropatches will be automatically downloaded to your computer and applied as needed. Once Zoom has fixed this issue, this micropatch will no longer be free and will only be available to 0patch PRO license holders.
Q: If I use 0patch to fix this vulnerability, what will happen when Zoom issues an updated version of Zoom Client for Windows?
A: 0patch is designed such that when a vulnerable executable module is replaced by a new version, any micropatches that were made for that vulnerable module automatically stop applying (because the cryptographic hash of the module changes). When Zoom issues an updated Client for Windows and you install it on your computer, our micropatch will become obsolete. In case this updated Zoom Client does not fix this vulnerability, we'll port the micropatch and make it available for free as quickly as possible.
Q: How do I know that the micropatch was actually applied to my Zoom Client?
A: First launch Zoom, then open 0patch Console and view the log. You should be able to find log entries like "Patch ... applied in application Zoom.exe"
Q: I installed 0patch Agent to fix this vulnerability but it is showing a large amount of popups notifying me about missing patches regardless of popup settings in 0patch Console. What can I do to make this stop?
A: We're aware that popups in the FREE plan have become pretty disturbing due to the increased amount of patches, and are
fixing that in the next agent version scheduled to be out next week. If you can't wait, feel free to download the current 0patch Agent release candidate and install it on top of your already installed 0patch Agent. When this release candidate is installed, 0patch Console will show that a “New agent is available”. Please ignore that – the server simply tells the agent that the version it is running is not the current official version. The message will stop appearing when the new agent is officially released.
[Below FAQ added on 7/13/2020]
Q: Why did you drop a 0day without giving the vendor the usual 90 days to fix the issue?
A: We have to be perfectly clear here: we did not "drop a 0day". We took extra care not to reveal any technical details. "Dropping a
0day" implies publishing details that allow anyone skilled to reproduce
the bug and create an exploit. In over two decades of existence, our company has never "dropped a 0day",
moreover we have never published details of unpatched vulnerabilities we
had reported to various vendors even if they took extremely long to fix
them (while it is standard practice to publish after 90 days). We took
the time to write up a detailed report we sent to Zoom, and we took care
of our users by providing them with a micropatch. This is what every
antivirus/antimalware company does for their users, e.g., by immediately
providing signatures for 0days.
Q: Now that Zoom has issued a new version of Client for Windows that fixes this issue, will you publish vulnerability details and proof-of-concept?
A: Our data shows that on the day we issued our micropatches, many 0patch users have been using all supported versions of Zoom Client for Windows instead of the latest one despite of its highly persistent auto-update mechanism. Taking our user base as a statistical sample of the global Zoom user base, this implies a significant amount of Zoom Clients will likely remain vulnerable even though a fixed version is now available. To prevent putting Zoom users who don't also use 0patch at risk, we will not publish any additional details at this time.
Q: Does this vulnerability show that Windows 7 is an insecure operating system?
A: While it may sound so, it really does not. This vulnerability is not a fault of Windows 7 in any way, but just happens to be exploitable there. It is not blocked by some security feature or exploit mitigation on Windows 8 and Windows 10 which isn't there on Windows 7, but by sheer coincidence.
Q: Isn't Windows 7 insecure anyway because Microsoft stopped supporting it?
A: Not really - Microsoft is still providing all critical and important security updates for Windows 7 until January 2023; from security perspective, Windows 7 is therefore effectively just as supported as Windows 10 as long as you're using Microsoft's Extended Security Updates, or, alternatively and less expensively, 0patch.
Community Outreach
We'd
like to thank the security researcher who shared the vulnerability with
us so we could provide quick protection for our existing users and everyone else affected. We're very pleased to see an increase of such
collaboration within security community and call upon all security
researchers to help us protect users and share vulnerability information
with us, whether or not they have also shared it with the original vendor.
We'll do our best to turn your reports into patches as quickly as possible. Thank you all!
Windows 7 and Server 2008 R2 users without Extended Security Updates
have just received a micropatch for CVE-2020-1299, another
"Stuxnet-like" critical LNK remote code execution issue that can get
code executed on user's computer just by viewing a folder with Windows
Explorer.
This vulnerability was patched by Microsoft with June 2020 Updates, but
Windows 7 and Server 2008 users without Extended Security Updates
remained vulnerable.
Security researcher Lê Hữu Quang Linh (@linhlhq) found this vulnerability, published a
detailed analysis and shared a POC with us so we could reproduce the
issue and create a micropatch.
We narrowed the root cause down to the order in which method CKnownFoldersFolder::_ClearCachedObjects (1) deletes a DSA object using a
call to DSA_DestroyCallback and (2) NULLs a pointer to said object. In
vulnerable code, it does it in this order; in patched code, vice versa, as seen on the image below.
Unpatched (left) and patched (right) function CKnownFoldersFolder::_ClearCachedObjects
Microsoft's patch also moved a CoTaskMemFree call to another code block
but we determined that to have no relevant consequence. Therefore, our
micropatch only needed one single instruction to NULL the pointer to the
DSA object before the call to DSA_DestroyCallback.
and qword[rbx+0xb8], 0; put 0 at rbx+0xb8, which contains a circular pointer to the same ; structure and is going to be deleted twice. ; When the function tries to recursively delete this structure, it follows ; this pointer and causes a double free code_end patchlet_end
Here's a video of our micropatch in action:
We'd like to thank security researcher Lê Hữu Quang Linh (@linhlhq)
for a detailed analysis and for sharing their POC with us, which
allowed us to quickly reproduce the issue and produce this micropatch
for Windows users without official security updates..
This
micropatch is immediately available to all 0patch users with a PRO
license, and is targeted at Windows 7 and Windows Server 2008 R2 users
without Extended Security Updates. To obtain the micropatch and have it
applied on your
computer(s) along with other micropatches included with a PRO license,
create an account in 0patch Central, install 0patch Agent and register it to your account. Note that no computer restart is needed for installing the agent or applying/un-applying any 0patch micropatch.
To learn more about 0patch, please visit our Help Center.
Windows 7 and Server 2008 R2 users without Extended Security Updates
have just received a micropatch for CVE-2020-1281, an integer overflow
vulnerability in Windows OLE marshaling that could allow a remote
attacker to execute arbitrary code on user's computer.
This vulnerability was patched by Microsoft with June 2020 Updates, but
Windows 7 and Server 2008 R2 users without Extended Security Updates
remained vulnerable.
Security researcher Yuki Chen found the vulnerability, wrote an in-depth analysis, analyzed
Microsoft's patch and provided a POC for triggering the vulnerability.
The vulnerability is in the way new object size is being calculated when
an object is enlarged (e.g., in string concatenation). This new size is
then used for allocating memory for the resulting "enlarged" object.
The vulnerable code doesn't account for really large numbers where
adding would exceed the capacity of 32-bit numbers. In such cases, an
integer overflow occurs, a too-small memory block is allocated, and
subsequent copying to this new block overwrites memory outside of it.
Microsoft's patch modified several functions related to calculating the
object size. We decided to only patch the one that is proven to be
exploitable at this point (BSTR_UserSize). Upon detecting an overflow,
our patch reports "Exploit Blocked" and terminates the process:
; This patchlet is located in BSTR_UserSize and replaces the main branch of code right up to the retn ; On entry we have: ; - rax points to the content of the BSTR object (the first character of the string) ; - rdx is the size to be added to the string ; - ecx is rdx+3 (just computed using "lea ecx, [rdx+3]) ; The patch performs the same operations the original code does, but for each of them, ; it checks for a numeric overflow and if so, pops ExploitBlocked and triggers an exception like the official patch
code_start
and ecx, 0xFFFFFFFC ; we pushed this instruction out, so replacing it here cmp ecx, edx ; check if adding 3 and aligning resulted in an overflow jb OVERFLOW ; overflow detected
test eax, eax ; same as in original code jz BSTR_IS_NULL mov eax, dword [rax-4] ; same as in original code jmp END1 BSTR_IS_NULL: xor eax, eax ; same as in original code END1:
add eax, 1 ; original code has "inc eax", but that doesn't set the carry flag jc OVERFLOW ; overflow would set the carry flag and eax, 0xFFFFFFFE
add eax, ecx jc OVERFLOW ; overflow would set the carry flag
add eax, 0x0C jc OVERFLOW ; overflow would set the carry flag
We'd like to thank Yuki Chen
for an excellent analysis and POC for this issue, which allowed us to
create a micropatch for Windows users without security updates.
This
micropatch is immediately available to all 0patch users with a PRO
license, and is targeted at Windows 7 and Windows Server 2008 R2 users without Extended Security Updates. To obtain the micropatch and have it applied on your
computer(s) along with other micropatches included with a PRO license,
create an account at 0patch Central, install 0patch Agent and register it to your account. Note that no computer restart is needed for installing the agent or applying/un-applying any 0patch micropatch.
To learn more about 0patch, please visit our Help Center.
