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Researchers say trojanized CWP web server hides Linux backdoor
XLab researchers told BleepingComputer that CWPdoor is spread by replacing Control Web Panel's cwpsrv binary with a passive, log-suppressing Linux backdoor.
Researchers at XLab, the research arm of QiAnXin Technology Group, say a Linux backdoor they call CWPdoor is being installed by replacing cwpsrv, the web server used by Control Web Panel, with a trojanized copy, BleepingComputer reported Nov. 51.
Control Web Panel, formerly CentOS Web Panel, is an open-source hosting control panel for web, email, DNS, and database services1. XLab said more than 340,000 CWP instances were exposed on the public web over the past month1.
XLab said it found the malware on June 29 after capturing a script that posed as an updater and swapped legitimate cwpsrv versions 1.15.10 and 1.24.0 for a malicious binary1. The script restored timestamps, deleted temporary files, and wiped command-history logs, according to the report1.
CWPdoor stays dormant until an attacker sends a crafted request with encrypted command data in an X-Ngx-Integrity-Data header, plus timestamp and RSA signature headers1. Commands and output use AES-256-CBC encryption1.
The backdoor checks that the timestamp is within a five-minute window and verifies the signature before handing the command to a helper process1. XLab said binding those fields and enforcing a plus-or-minus 300-second window provides replay protection1.
The implant also tampers with the server logging module so the triggering request does not appear in access logs, BleepingComputer said, citing XLab1.
After the first script, researchers saw CWPdoor uploaded to VirusTotal on Sept. 30 in an archive that also included the Ebury Linux backdoor1. The malicious cwpsrv file in that archive had zero detections at the time1.
XLab said that sample indicated real victims, and that any operational link between Ebury and CWPdoor remains unclear1. Ebury is a long-running Linux credential-stealing botnet; BleepingComputer noted an ESET report from May 2024 that attributed nearly 400,000 server infections since 20091.
XLab recommended checking for an ngx_http_integrity_helper Unix socket, suspicious cwpsrv helper processes, and X-Ngx-Integrity strings in the server binary1. If compromise is confirmed, it advised replacing the binary, upgrading, rotating control-panel credentials, and hunting for other malware1.
BleepingComputer did not quote a statement from Control Web Panel's maintainers, and XLab did not publish a confirmed victim count beyond the VirusTotal sample and the exposed-instance figure1.
