Category Archives: Zero-Day Vulnerability

Microsoft Issues Patch for Windows Zero-Day Flaw Under Active Attack

Microsoft today, on its year-end December Patch Tuesday, released security updates to patch a total 39 vulnerabilities its Windows operating systems and applications—10 of which are rated as critical and other important in severity. One of the security vulnerabilities patched by the tech giant this month is listed as publicly known at the time of release, and one is a zero-day reported as being

New Adobe Flash Zero-Day Exploit Found Hidden Inside MS Office Docs

Cybersecurity researchers have discovered a new zero-day vulnerability in Adobe Flash Player that hackers are actively exploiting in the wild as part of a targeted campaign appears to be attacking a Russian state health care institution. The vulnerability, tracked as CVE-2018-15982, is a use-after-free flaw resides in Flash Player that, if exploited successfully, allows an attacker to execute

0-Days Found in iPhone X, Samsung Galaxy S9, Xiaomi Mi6 Phones

At Pwn2Own 2018 mobile hacking competition held in Tokyo on November 13-14, white hat hackers once again demonstrated that even the fully patched smartphones running the latest version of software from popular smartphone manufacturers can be hacked. Three major flagship smartphones—iPhone X, Samsung Galaxy S9, and Xiaomi Mi6—were among the devices that successfully got hacked at the annual

63 New Flaws (Including 0-Days) Windows Users Need to Patch Now

It's Patch Tuesday once again…time for another round of security updates for the Windows operating system and other Microsoft products. This month Windows users and system administrators need to immediately take care of a total of 63 security vulnerabilities, of which 12 are rated critical, 49 important and one moderate and one low in severity. <!-- adsense --> Two of the vulnerabilities

Unpatched VirtualBox Zero-Day Vulnerability and Exploit Released Online

An independent exploit developer and vulnerability researcher has publicly disclosed a zero-day vulnerability in VirtualBox—a popular open source virtualization software developed by Oracle—that could allow a malicious program to escape virtual machine (guest OS) and execute code on the operating system of the host machine. The vulnerability occurs due to memory corruption issues and affects

FireEye Uncovers CVE-2017-8759: Zero-Day Used in the Wild to Distribute FINSPY

FireEye recently detected a malicious Microsoft Office RTF document that leveraged CVE-2017-8759, a SOAP WSDL parser code injection vulnerability. This vulnerability allows a malicious actor to inject arbitrary code during the parsing of SOAP WSDL definition contents. FireEye analyzed a Microsoft Word document where attackers used the arbitrary code injection to download and execute a Visual Basic script that contained PowerShell commands.

FireEye shared the details of the vulnerability with Microsoft and has been coordinating public disclosure timed with the release of a patch to address the vulnerability and security guidance, which can be found here.

FireEye email, endpoint and network products detected the malicious documents.

Vulnerability Used to Target Russian Speakers

The malicious document, “Проект.doc” (MD5: fe5c4d6bb78e170abf5cf3741868ea4c), might have been used to target a Russian speaker. Upon successful exploitation of CVE-2017-8759, the document downloads multiple components (details follow), and eventually launches a FINSPY payload (MD5: a7b990d5f57b244dd17e9a937a41e7f5).

FINSPY malware, also reported as FinFisher or WingBird, is available for purchase as part of a “lawful intercept” capability. Based on this and previous use of FINSPY, we assess with moderate confidence that this malicious document was used by a nation-state to target a Russian-speaking entity for cyber espionage purposes. Additional detections by FireEye’s Dynamic Threat Intelligence system indicates that related activity, though potentially for a different client, might have occurred as early as July 2017.

CVE-2017-8759 WSDL Parser Code Injection

A code injection vulnerability exists in the WSDL parser module within the PrintClientProxy method ( - System.Runtime.Remoting/metadata/wsdlparser.cs,6111). The IsValidUrl does not perform correct validation if provided data that contains a CRLF sequence. This allows an attacker to inject and execute arbitrary code. A portion of the vulnerable code is shown in Figure 1.

Figure 1: Vulnerable WSDL Parser

When multiple address definitions are provided in a SOAP response, the code inserts the “//base.ConfigureProxy(this.GetType(),” string after the first address, commenting out the remaining addresses. However, if a CRLF sequence is in the additional addresses, the code following the CRLF will not be commented out. Figure 2 shows that due to lack validation of CRLF, a System.Diagnostics.Process.Start method call is injected. The generated code will be compiled by csc.exe of .NET framework, and loaded by the Office executables as a DLL.

Figure 2: SOAP definition VS Generated code

The In-the-Wild Attacks

The attacks that FireEye observed in the wild leveraged a Rich Text Format (RTF) document, similar to the CVE-2017-0199 documents we previously reported on. The malicious sampled contained an embedded SOAP monikers to facilitate exploitation (Figure 3).

Figure 3: SOAP Moniker

The payload retrieves the malicious SOAP WSDL definition from an attacker-controlled server. The WSDL parser, implemented in of .NET framework, parses the content and generates a .cs source code at the working directory. The csc.exe of .NET framework then compiles the generated source code into a library, namely http[url path].dll. Microsoft Office then loads the library, completing the exploitation stage.  Figure 4 shows an example library loaded as a result of exploitation.

Figure 4: DLL loaded

Upon successful exploitation, the injected code creates a new process and leverages mshta.exe to retrieve a HTA script named “word.db” from the same server. The HTA script removes the source code, compiled DLL and the PDB files from disk and then downloads and executes the FINSPY malware named “left.jpg,” which in spite of the .jpg extension and “image/jpeg” content-type, is actually an executable. Figure 5 shows the details of the PCAP of this malware transfer.

Figure 5: Live requests

The malware will be placed at %appdata%\Microsoft\Windows\OfficeUpdte-KB[ 6 random numbers ].exe. Figure 6 shows the process create chain under Process Monitor.

Figure 6: Process Created Chain

The Malware

The “left.jpg” (md5: a7b990d5f57b244dd17e9a937a41e7f5) is a variant of FINSPY. It leverages heavily obfuscated code that employs a built-in virtual machine – among other anti-analysis techniques – to make reversing more difficult. As likely another unique anti-analysis technique, it parses its own full path and searches for the string representation of its own MD5 hash. Many resources, such as analysis tools and sandboxes, rename files/samples to their MD5 hash in order to ensure unique filenames. This variant runs with a mutex of "WininetStartupMutex0".


CVE-2017-8759 is the second zero-day vulnerability used to distribute FINSPY uncovered by FireEye in 2017. These exposures demonstrate the significant resources available to “lawful intercept” companies and their customers. Furthermore, FINSPY has been sold to multiple clients, suggesting the vulnerability was being used against other targets.

It is possible that CVE-2017-8759 was being used by additional actors. While we have not found evidence of this, the zero day being used to distribute FINSPY in April 2017, CVE-2017-0199 was simultaneously being used by a financially motivated actor. If the actors behind FINSPY obtained this vulnerability from the same source used previously, it is possible that source sold it to additional actors.


Thank you to Dhanesh Kizhakkinan, Joseph Reyes, FireEye Labs Team, FireEye FLARE Team and FireEye iSIGHT Intelligence for their contributions to this blog. We also thank everyone from the Microsoft Security Response Center (MSRC) who worked with us on this issue.

Acknowledgement of Attacks Leveraging Microsoft Zero-Day

FireEye recently detected malicious Microsoft Office RTF documents that leverage a previously undisclosed vulnerability. This vulnerability allows a malicious actor to execute a Visual Basic script when the user opens a document containing an embedded exploit. FireEye has observed several Office documents exploiting the vulnerability that download and execute malware payloads from different well-known malware families.

FireEye shared the details of the vulnerability with Microsoft and has been coordinating for several weeks public disclosure timed with the release of a patch by Microsoft to address the vulnerability. After recent public disclosure by another company, this blog serves to acknowledge FireEye’s awareness and coverage of these attacks.

FireEye email and network solutions detect the malicious documents as: Malware.Binary.Rtf.

Attack Scenario

The attack involves a threat actor emailing a Microsoft Word document to a targeted user with an embedded OLE2link object. When the user opens the document, winword.exe issues a HTTP request to a remote server to retrieve a malicious .hta file, which appears as a fake RTF file. The Microsoft HTA application loads and executes the malicious script. In both observed documents the malicious script terminated the winword.exe process, downloaded additional payload(s), and loaded a decoy document for the user to see. The original winword.exe process is terminated in order to hide a user prompt generated by the OLE2link.

The vulnerability is bypassing most mitigations; however, as noted above, FireEye email and network products detect the malicious documents. Microsoft Office users are recommended to apply the patch as soon as it is available. 


FLARE Team, FireEye Labs Team, FireEye iSIGHT Intelligence, and Microsoft Security Response Center (MSRC).