Attackers Exploiting WebLogic Servers via CVE-2020-14882 to install Cobalt Strike
Last Updated: 2020-11-04 13:50:55 UTC
by Renato Marinho (Version: 1)
Starting late last week, we observed a large number of scans against our WebLogic honeypots to detect if they are vulnerable to CVE-2020-14882. CVE-2020-14882 was patched about two weeks ago as part of Oracle's quarterly critical patch update. In addition to scans simply enumerating vulnerable servers, we saw a small number of scans starting on Friday (Oct. 30th) attempting to install crypto-mining tools .
On Friday, Oracle amended its patch for CVE-2020-14882 . A new variation of the vulnerability (CVE-2020-14750) can be used to exploit WebLogic servers with a trivial modification of the exploit code.
Last Saturday we started seeing a campaign using a chain of Powershell obfuscated scripts to download a Cobalt Strike payload. According to Cisco Talos Q4 2020 CTIR report, 66% of all ransomware attacks this quarter involved the use of Cobalt Strike . Thus, as expected, there is a high probability ransomware gang included CVE-2020-14882 exploit in their arsenal.
The attack, as seen in Figure 1, exploits the vulnerability to execute a PowerShell payload base64-encoded.
Figure 1 - Payload delivery
Decoding the base64 content, we can find the following code. As seen, there is another encoding layer using base64 and gzip compression. I usually make some adjustments to the original malicious script to make it save the decoded content to a file. So, replacing “IEX” by “$content =” and appending the script with “$content |out-file -filepath decoded_script.ps1” is enough to accomplish this result for this case.
Figure 2 - First stage decoding
Part of the resulting code is shown in Figure 3. Notice that there is another protected code. There is a loop decrypting each byte of the code using an XOR function with the byte 0x35.
Figure 3 - Second stage decoding
The result of this operation is a shellcode to download and execute a Cobalt Strike payload hosted at http://185[.]205.210.179:4321/Z8qZ.
Figure 4 - Cobalt Strike payload download
Submitting the binary to VirusTotal, we had the following result:
Figure 5 - Cobalt Strike payload submitted to Virus Total
Running the malicious scripts in a controlled environment, it was possible to see connections established from time to time with the C2 at http://185[.]205.210.179/en_US/all.js.
The malicious requests are available at https://isc.sans.edu/WebLogicPS.log.zip
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