Oct 26 2017

Analyzing Microsoft Office Zero-Day Exploit CVE-2017-11826: Memory Corruption Vulnerability

McAfee Labs has performed frequent analyses of Office-related threats over the years: In 2015, we presented research on the Office OLE mechanism; in 2016 at the BlueHat conference, we looked at the high-level attack surface of Office; and this year at the SYSCAN360 Seattle conference, we presented deep research on the critical Office “Moniker” zero-day vulnerabilities.

This month, Microsoft released an update for an Office zero-day attack. We examined an in-the-wild sample, and with this post we share our findings to help others understand the threat.

The sample arrives as an RTF file, and embeds at least three objects (through the control word “\object”). This is a memory corruption vulnerability, so it needs additional steps to archive the full exploitation.

1. The first object, in the following figure, shows that it loads a COM object whose CLASSID is D5DE8D20-5BB8-11D1-A1E3-00A0C90F2731.

 

If we look into the Windows registry, we see that the COM DLL C:\Windows\system32\msvbvm60.dll will be loaded. The purpose of loading this DLL is that msvbvm60.dll is not compatible with address space layout randomization (ASLR), thus it can be used to bypass ASLR and data execution prevention (DEP) on older Office versions. (We will explain later.) This is not a new trick; researcher Parvez Anwar described this process in 2015.

2. The second object is a .docx file that employs the ActiveX.bin technique to spray the heap, also not a new trick. McAfee Labs first identified this exploitation technique in a zero-day attack discovery in 2013; our colleague Debasish Mandal discussed this technique in one of his recent posts.

3. The third object is the cause of this vulnerability. It is an embedded .docx file. When this .docx is rendered, a memory corruption vulnerability is triggered. Specifically, we have identified the problem is due to mishandling of nested tags in the Office Open XML format. The key tags follow:

With help from the first and the second steps, an attacker can hijack the program’s control flow to a predictable address in msvbvm60.dll’s code by exploiting the memory corruption vulnerability. This is the classic step of “stack pivot” for defeating ASLR and DEP. (See the next figure.) Following the return-oriented programming chain and shellcode comes the main payload, which we will not discuss in this post.

This exploitation technique works only on older Office versions. Since Office 2013, Microsoft has employed the security feature Forced-ASLR. As its name suggests, the feature forces the randomization of a module’s loading address even if the DLL is not ASLR compatible. Thus this in-the-wild attack can work only on Office 2010 and older versions. Nonetheless, because the underlying vulnerability does affect newer versions of Office, we recommend that all Office users install the official patch as soon as possible.

For McAfee NSP customers, we have released signature 0x45219c00 (UDS-HTTP: Microsoft Office Memory Corruption Vulnerability (CVE-2017-11826)) to prevent this attack.

Thanks to my colleague Bing Sun for his help with the analysis.

The post Analyzing Microsoft Office Zero-Day Exploit CVE-2017-11826: Memory Corruption Vulnerability appeared first on McAfee Blogs.

Nov 09 2016

Krebs on Security 2016-11-09 13:55:39

Let’s get this out of the way up front: Having “2016 election” in the headline above is probably the only reason anyone might read this story today. It remains unclear whether Republicans and Democrats can patch things up after a bruising and divisive election, but thanks to a special Election Day Patch Tuesday hundreds of millions of Adobe and Microsoft users have some more immediate patching to do.

As the eyes of the world stayed glued to screens following the U.S. presidential election through the night, Microsoft and Adobe were busy churning out a large number of new security updates for Windows, MS Office, Flash Player and other software. If you use Flash Player or Microsoft products, please take a deep breath and read on.

brokenwindows

Regularly scheduled on the second Tuesday of each month, this month’s “Patch Tuesday” fell squarely on Election Day in the United States and included 14 patch bundles. Those patches fixed a total of 68 unique security flaws in Windows and related software.

Six of the 14 patches carry Microsoft’s most’s-dire “critical” label, meaning they fix bugs that malware or miscreants could use to remotely compromise vulnerable PCs without any help from users apart from maybe visiting a hacked or malicious Web site.

Microsoft says two of the software flaws addressed this week are already being exploited in active attacks. It also warned that three of the software vulnerabilities were publicly detailed prior to the release of these fixes – potentially giving attackers a head start in figuring out how to exploit the bugs.

MS16-129 is our usual dogs breakfast of remote code execution vulnerabilities in the Microsoft Edge browser, impacting both HTML rendering and scripting,” said Bobby Kuzma, systems engineer at Core Security. “MS16-130 contains  a privilege escalation in the onscreen keyboard function from Vista forward. That’s great news for anyone running touchscreen kiosks that are supposedly locked down.”

As part of a new Microsoft policy that took effect last month, home and business Windows users will no longer be able to pick and choose which updates to install and which to leave for another time. Consumers on Windows 7 Service Pack 1 and Windows 8.1 will henceforth receive what Redmond is calling a “Monthly Rollup,” which addresses both security issues and reliability issues in a single update. The “Security-only updates” option — intended for enterprises and not available via Windows Update —  will only include new security patches that are released for that month. What this means is that if any part of the patch bundle breaks, the only option is to remove the entire bundle (instead of the offending patch, as was previously possible). 

brokenflash-aIt’s important to note that several update types won’t be included in a rollup, including those released for Adobe Flash Player on Tuesday. For the second time this month, Adobe issued a critical update for its ubiquitous Flash Player browser plugin. The newest Flash version — v.  23.0.0.207 and available here for both Windows and Mac computers — plugs at least nine more flaws in Flash. To see if you have Flash installed and if so what version is running, check this link.

Google users may need to restart the browser to install or automatically download the latest version. When in doubt, click the vertical three dot icon to the right of the URL bar, select “Help,” then “About Chrome”: If there is an update available, Chrome should install it then.

Somehow KrebsonSecurity neglected to mention the other critical update Adobe pushed for Flash on Oct. 26, 2016 (my bad folks, sorry). It’s really hard to keep up with Flash updates sometimes. That’s part of the reason I’ll continue to encourage readers to disable or remove Adobe Flash unless until it is needed for something specific. Fewer sites now require it, and leaving this buggy, powerful program enabled all the time is just asking for security trouble. Check out the advice at A Month Without Adobe Flash Player for tips on how to hobble or do without Flash entirely.

Indeed, Google reportedly is planning to phase out full support for Flash on its Chrome browser by the end of 2016. And Mozilla is now blocking certain Flash content deemed “not essential to the the user experience.” Specifically, as stated by Mozilla’s Benjamin Smedberg, Mozilla Firefox is blocking specific Flash content that is invisible to users.

“This is expected to reduce Flash crashes and hangs by up to 10%. To minimize website compatibility problems, the changes are initially limited to a short, curated list of Flash content that can be replaced with HTML,” Smedberg wrote back in June. “We intend to add to this list over time.”

For more on this week’s patches, check out coverage from security firms Qualys and Shavlik. And, as always, if you experience any issues downloading or installing any of these updates, please leave a note about it in the comments below.

Oct 31 2016

Trick or Treat! Google issues warning of critical Windows vulnerability in wild

Enlarge / Win32k.sys has some problems. Again.

Recently, Google’s Threat Analysis Group discovered a set of zero-day vulnerabilities in Adobe Flash and the Microsoft Windows kernel that were already being actively used by malware attacks against the Chrome browser. Google alerted both Adobe and Microsoft of the discovery on October 21, and Adobe issued a critical fix to patch its vulnerability last Friday. But Microsoft has yet to patch a critical bug in the Windows kernel that allows these attacks to work—which prompted Google to publicly announce the vulnerabilities today.

“After 7 days, per our published policy for actively exploited critical vulnerabilities, we are today disclosing the existence of a remaining critical vulnerability in Windows for which no advisory or fix has yet been released,” wrote Neel Mehta and Billy Leonard of Google’s Threat Analysis Group.”This vulnerability is particularly serious because we know it is being actively exploited.”

The bug being exploited could allow an attacker to escape from Windows’ security sandbox. The sandbox, which normally allows only user-level applications to execute, lets programs execute without needing administrator access while isolating what it can access on the local system through a set of policies.

Read 2 remaining paragraphs | Comments

Oct 11 2016

Krebs on Security 2016-10-11 14:51:21

Adobe and Microsoft today each issued updates to fix critical security flaws in their products. Adobe’s got fixes for Acrobat and Flash Player ready. Microsoft’s patch bundle for October includes fixes for at least five separate “zero-day” vulnerabilities — dangerous flaws that attackers were already exploiting prior to today’s patch release. Also notable this month is that Microsoft is changing how it deploys security updates, removing the ability for Windows users to pick and choose which individual patches to install.

brokenwindowsZero-day vulnerabilities describe flaws that even the makers of the targeted software don’t know about before they start seeing the flaws exploited in the wild, meaning the vendor has “zero days” to fix the bugs.

According to security vendor Qualys, Patch Tuesday updates fix zero-day bugs in Internet Explorer and Edge — the default browsers on different versions of Windows. MS16-121 addresses a zero-day in Microsoft Office. Another zero-day flaw affects GDI+ — a graphics component built into Windows that can be exploitable through the browser. The final zero-day is present in the Internet Messaging component of Windows.

Starting this month, home and business Windows users will no longer be able to pick and choose which updates to install and which to leave for another time. For example, I’ve often advised home users to hold off on installing .NET updates until all other patches for the month are applied — reasoning that .NET updates are very large and in my experience have frequently been found to be the source of problems when applying huge numbers of patches simultaneously.

But that cafeteria-style patching goes out the…err…Windows with this month’s release. Microsoft made the announcement in May of this year and revisited the subject again in August to add more detail behind its decision:

“Historically, we have released individual patches for these platforms, which allowed you to be selective with the updates you deployed,” wrote Nathan Mercer, a senior product marketing manager at Microsoft. “This resulted in fragmentation where different PCs could have a different set of updates installed leading to multiple potential problems:

  • Various combinations caused sync and dependency errors and lower update quality
  • Testing complexity increased for enterprises
  • Scan times increased
  • Finding and applying the right patches became challenging
  • Customers encountered issues where a patch was already released, but because it was in limited distribution it was hard to find and apply proactively

By moving to a rollup model, we bring a more consistent and simplified servicing experience to Windows 7 SP1 and 8.1, so that all supported versions of Windows follow a similar update servicing model. The new rollup model gives you fewer updates to manage, greater predictability, and higher quality updates. The outcome increases Windows operating system reliability, by eliminating update fragmentation and providing more proactive patches for known issues. Getting and staying current will also be easier with only one rollup update required. Rollups enable you to bring your systems up to date with fewer updates, and will minimize administrative overhead to install a large number of updates.”

Microsoft’s patch policy changes are slightly different for home versus business customers. Consumers on Windows 7 Service Pack 1 and Windows 8.1 will henceforth receive what Redmond is calling a “Monthly Rollup,” which addresses both security issues and reliability issues in a single update. The “Security-only updates” option — intended for enterprises and not available via Windows Update —  will only include new security patches that are released for that month. 

What this means is that if any part of the patch bundle breaks, the only option is to remove the entire bundle (instead of the offending patch, as was previously possible). I have no doubt this simplifies things for Microsoft and likely saves them a ton of money, but my concern is this will leave end-users unable to apply critical patches simply due to a single patch breaking something.

It’s important to note that several update types won’t be included in a rollup, including those for Adobe Flash Player. As it happens, Adobe today issued an update for its Flash Player browser plugin that fixes a dozen security vulnerabilities in the program. The company said it is currently not aware of any attempts to exploit these flaws in the wild (i.e., no zero-days in this month’s Flash patch).

brokenflash-aThe latest update brings Flash to v. 23.0.0.185 for Windows and Mac users alike. If you have Flash installed, you should update, hobble or remove Flash as soon as possible. To see which version of Flash your browser may have installed, check out this page.

The smartest option is probably to ditch the program once and for all and significantly increase the security of your system in the process. I’ve got more on that approach (as well as slightly less radical solutions ) in A Month Without Adobe Flash Player.

If you choose to update, please do it today. The most recent versions of Flash should be available from this Flash distribution page or the Flash home page. Windows users who browse the Web with anything other than Internet Explorer may need to apply this patch twice, once with IE and again using the alternative browser (Firefox, Opera, e.g.). Chrome and IE should auto-install the latest Flash version on browser restart (users may need to manually check for updates in and/or restart the browser to get the latest Flash version).

Finally, Adobe released security updates that correct a whopping 71 flaws in its PDF Reader and Acrobat products. If you use either of these software packages, please take a moment to update them.