Evaluation of two arbitrary code execution vulnerabilities affecting WPS Workplace -

ESET researchers found a code execution vulnerability in WPS Workplace for Home windows (CVE⁠-⁠2024⁠-⁠7262), because it was being exploited by APT-C-60, a South Korea-aligned cyberespionage group. Upon analyzing the basis trigger, we subsequently found one other strategy to exploit the defective code (CVE-2924-7263). Following a coordinated disclosure course of, each vulnerabilities are actually patched – on this blogpost, we offer technical particulars.

Key factors of the blogpost:

APT-C-60 weaponized a code execution vulnerability in WPS Workplace for Home windows (CVE-2024-7262) with the intention to goal East Asian international locations.

A root trigger evaluation of this vulnerability is offered together with an outline of its weaponization.

The examine of the exploit led ESET researchers to the invention of an alternate path to use the vulnerability (CVE-2024-7263).

Overview

Whereas investigating APT-C-60 actions, we discovered a wierd spreadsheet doc referencing one of many group’s many downloader elements. Our evaluation led us to the invention of a code execution vulnerability in WPS Workplace for Home windows being exploited within the wild by APT-C-60 to focus on East Asian international locations. The ultimate payload is a customized backdoor we internally named SpyGlace, publicly documented by ThreatBook as TaskControler.dll.

In response to the WPS web site, this software program has over 500 million energetic customers worldwide, which makes it an excellent goal to succeed in a considerable variety of people within the East Asia area. Throughout our coordinated vulnerability disclosure course of, DBAPPSecurity independently revealed an evaluation of the weaponized vulnerability and confirmed that APT-C-60 has exploited the vulnerability to ship malware to customers in China.

The malicious doc (SHA-1: 7509B4C506C01627C1A4C396161D07277F044AC6) comes as an MHTML export of the generally used XLS spreadsheet format. Nevertheless, it accommodates a specifically crafted and hidden hyperlink designed to set off the execution of an arbitrary library if clicked when utilizing the WPS Spreadsheet software. The relatively unconventional MHTML file format permits a file to be downloaded as quickly because the doc is opened; subsequently, leveraging this method whereas exploiting the vulnerability gives for distant code execution. Determine 1 exhibits how the doc is displayed in WPS Spreadsheet: a picture of rows and columns referencing the Coremail e-mail answer, used as a decoy. The picture hides the malicious hyperlink.

Evaluation of two arbitrary code execution vulnerabilities affecting WPS Workplace — *Determine 1. The exploit doc embeds an image hiding the malicious hyperlink*

Following our coordinated vulnerability disclosure coverage, from the second the weaponized doc was uploaded to VirusTotal to the discharge of this blogpost, the next timeline was noticed:

2024-02-29: The exploit doc for CVE-2024-7262 was uploaded to VirusTotal.
2024-03-??: Kingsoft launched an replace that silently patched the CVE-2024-7672 vulnerability in order that the 2024-02-29 exploit not labored. This was decided retrospectively, by analyzing all accessible WPS Workplace releases between 2024-03 and 2024-04, as Kingsoft was not particularly forthcoming in offering exact particulars of its actions when trying to restore this vulnerability.
2024-04-30: We analyzed the malicious doc from VirusTotal and found it was actively exploiting CVE-2024-7262, which was a zero-day vulnerability on the time of the doc’s preliminary use. We additionally found that Kingsoft’s silent patch addressed just one a part of the defective code, and the remaining flawed code was nonetheless exploitable.
2024-05-25: We contacted Kingsoft to report our findings. Whereas the primary vulnerability was already patched, we requested if they might create a CVE entry and/or a public assertion as they’d for CVE-2022-24934.
2024-05-30: Kingsoft acknowledged the vulnerabilities and informed us they’d preserve us up to date.
2024-06-17: We requested for an replace.
2024-06-22: Kingsoft informed us the event group was nonetheless engaged on it and was aiming to repair this within the coming model.
2024-07-31: Based mostly on later exams, we discovered that CVE-2024-7263 was silently patched. We suggested Kingsoft that we had reserved and have been making ready CVE-2024-7262 and CVE-2024-7263.
2024-08-11: DBAPPSecurity group independently revealed its findings.
2024-08-15: CVE-2024-7262 and CVE-2024-7263 have been revealed.
2024-08-16: We requested Kingsoft for an additional replace.
2024-08-22: Kingsoft acknowledged it had fastened CVE-2024-7263 by the tip of Could, which contradicts the corporate’s declare on 2024-06-22 that its growth group “are nonetheless engaged on it”.
2024-08-28: Kingsoft has acknowledged each vulnerabilities and that it has patched each. Nevertheless, it has expressed little interest in publicizing the in-the-wild exploitation of CVE-2024-7262 so we are actually publishing this blogpost to warn Kingsoft’s clients that they need to urgently replace WPS Workplace as a consequence of in-the-wild exploitation and third-party disclosure of the CVE-2024-7262 vulnerability and exploit, which improve the probabilities of additional exploitation.

The CVE-2024-7262 vulnerability stemmed from the shortage of sanitization of an attacker-provided file path and lack of validation of the plugin being loaded. After analyzing its patch, we found one other strategy to exploit the vulnerability by leveraging an additional logic bug.

CVE-2024-7262

This part describes the bug exploited by APT-C-60 that enables code execution by way of hijacking the management movement of the WPS Workplace plugin element promecefpluginhost.exe. We additionally clarify how the vulnerability was triggered and weaponized within the form of a legitimate-looking spreadsheet doc.

Root trigger evaluation

When putting in WPS Workplace for Home windows, the software program suite registers a customized protocol handler referred to as ksoqing that enables the execution of an exterior software each time a person clicks on a URL beginning with the URI scheme ksoqing://. Within the Home windows working system, the registration of a customized protocol handler is completed within the registry. On this case, the default worth beneath the important thing HKCRksoqingshellopencommand directs Home windows to execute C:Customers<USER>AppDataLocalKingsoftWPS Workplace<VERSION>office6wps.exe with the argument /qingbangong “%1” the place %1 is changed with the total URL. As an example this, Determine 2 exhibits what occurs when a person clicks on a hyperlink utilizing the customized protocol ksoqing contained in the WPS Spreadsheet software (et.exe).

*Determine 2. The WPS Spreadsheet software begins* wps.exe to deal with the customized protocol ksoqing

Determine 3 gives an summary of the management movement of the exploit for CVE-2024-7262.

*Determine 3. Overview of the exploit’s management movement*

As soon as launched, wps.exe masses qingbangong.dll, the element liable for parsing and validating sure parameters from the hyperlink. The malicious hyperlink within the exploit file we discovered has the next format ksoqing://kind=ksolaunch&cmd=<base64-encoded string>&token=<MD5 hash>&launchname=promecefpluginhost.exe. In response to our evaluation and exams, this ends in launching an software already current on the system (on this case, promecefpluginhost.exe), with the attacker-provided base64-encoded command line.

The token parameter is the MD5 hash of the encoded worth of the cmd parameter concatenated with the string _qingLaunchKey_ adopted by the encoded worth of the launchname parameter. The final one should be an executable positioned beneath C:Customers<USER>AppDataLocalKingsoftWPS Workplace<VERSION>office6 and signed with a legitimate certificates from Kingsoft.

After decoding the cmd parameter, we discovered that the command line /qingbangong -CefParentID=1 -JSCefServicePath=<base64-encoded file path> is handed to promecefpluginhost.exe. After some initialization, the library ksojscore.dll is loaded and decodes the JSCefServicePath parameter. The result’s a string handed as a parameter to Qt’s QLibrary::load methodology. This file path is attacker-defined, which implies that an attacker may obtain code execution by loading an arbitrary DLL. Determine 4 illustrates how the attacker-controlled JSCefServicePath parameter is processed by ksojscore.dll.

*Determine 4. Parameter* JSCefServicePath *is decoded (left) and used as an argument for the QLibrary::load methodology (proper)*

Primarily, it’s doable to abuse the ksoqing scheme protocol and create a hyperlink that when clicked will load a library from a given distant file path. APT-C-60 weaponized the vulnerability to execute its first-stage trojan downloader element (SHA-1: 08906644B0EF1EE6478C45A6E0DD28533A9EFC29).

Exploiting the vulnerability

With a purpose to exploit this vulnerability, an attacker would want to retailer a malicious library someplace accessible by the focused pc both on the system or on a distant share, and know its file path prematurely. The exploit builders of this vulnerability knew a few tips that helped them obtain this.

Leveraging the MHTML format to obtain distant recordsdata

The authors of the exploit selected to leverage a particular function of the supported MHTML file format to have their malicious element downloaded and saved on the system in a predictable means. This specific kind of file is an export format supplied by Microsoft Phrase and Excel functions to permit customers to view paperwork of their browser. It’s a multipart archive containing HTML, CSS, and JavaScript recordsdata that facilitate the show of the doc. By inserting an img tag inside one of many HTML recordsdata, it’s doable to make the Spreadsheet software obtain a distant file when the doc is being loaded. As an illustration, Determine 5 exhibits certainly one of our check recordsdata with the img tag and its src component pointing to a library saved regionally.

When opening the spreadsheet doc with the WPS Spreadsheet et.exe software, the distant library is mechanically downloaded and saved on disk, as noticed utilizing ProcMon proven in Determine 6.

*Determine 6. The WPS Spreadsheet software downloads and shops our library on the system*

Discovering a predictable file path

As for the predictable file path downside, we discovered that the downloaded recordsdata are saved beneath %localappdatapercentTempwpsINetCache and the filename is the MD5 hash of the URL encoded in UTF‑16LE. As an illustration, our URL was http://localhost/Dll1.dll for which the MD5 hash is 914CBE6372D5B7C93ADDC4FEB5E964CD. Nevertheless, when attempting to set the variable JSCefServicePath to level to such a file path, it will get concatenated to the basis listing of the WPS Workplace software positioned beneath %localappdatapercentKingsoftWPS Workplace<VERSION>office6. If the file can’t be discovered, promecefpluginhost.exe will attempt to retrieve the library from different paths, as proven in Determine 7.

*Determine 7. The file path pointed to by* JSCefServicePath *is appended to the basis listing of WPS Workplace*

Nevertheless, it’s doable to make use of a relative path from the basis listing of the WPS Workplace software, corresponding to ……..TempwpsINetCache914cbe6372d5b7c93addc4feb5e964cd.

The file extension downside

There’s a final impediment to beat. An astute reader would have most likely seen that the .dll extension will get appended to the filename when the promecefpluginhost.exe course of tries to load the library. As seen in Determine 6, the extension will not be appended when the downloaded file is created. The authors of the exploit, as soon as once more, used their data of the Home windows API to bypass this restriction. As talked about earlier, the QLibrary::Load methodology is liable for loading the library which in flip calls LoadLibraryW. The documentation for the lpLibFileName parameter handed to this operate states that including a trailing dot character (.) prevents the operate from appending the .dll extension. Due to this fact, appending this character to the relative path would enable our library to get loaded.

Reproducing the exploit

When placing all of it collectively, with the intention to reproduce the exploit, we adopted these steps:

Host a customized library on an online server.
Compute the MD5 hash of the URL.
Construct the corresponding hyperlink.
Create a spreadsheet doc, insert the hyperlink, and export it as an MHTML file.
Insert an img tag contained in the exported file to level to the URL.

Determine 8 illustrates find out how to construct the hyperlink.

*Determine 8. Constructing the hyperlink*

After opening the doc, a single click on on the hyperlink triggered the vulnerability and our customized library was loaded as proven in Determine 9 and, in additional element, in Determine 10.

*Determine 9. Our customized library will get written to disk and loaded*

*Determine 10. Name stack element of our library being loaded*

When loaded, our customized library writes the PID, the presence of admin privileges, and the file path of the internet hosting course of to a log file. We reproduced the exploit for various variations of WPS Workplace for Home windows as illustrated in Determine 11.

Determine 11. Log file itemizing for weak WPS Workplace variations

Since this can be a one-click vulnerability, the exploit builders embedded an image of the spreadsheet’s rows and columns contained in the spreadsheet with the intention to deceive and persuade the person that the doc is a daily spreadsheet. The malicious hyperlink was linked to the picture in order that clicking on a cell within the image would set off the exploit, as reproduced in Determine 12.

*Determine 12. A misleading spreadsheet embedding a picture of normal rows and columns*

One other fascinating reality about this vulnerability is that it will also be triggered by way of a single click on within the preview pane in Home windows Explorer, which makes it much more harmful.

Affected variations

The affected variations of WPS Workplace for Home windows vary from 12.2.0.13110, launched round August 2023 till the discharge of the patch in March 2024 with model 12.1.0.16412. The weaponized doc was first uploaded to VirusTotal in February; some malicious elements, given their PE timestamp, have been inbuilt February.

CVE-2024-7263

This part gives an evaluation of the patch for CVE-2024-7262 and the ensuing discovery of one other code execution vulnerability by way of hijacking the management movement of the identical WPS Workplace plugin element: promecefpluginhost.exe.