A now-patched security flaw in Google Chrome was exploited as a zero-day by a threat actor known as TaxOff to deploy a backdoor codenamed Trinper.
The attack, observed in mid-March 2025 by Positive Technologies, involved the use of a sandbox escape vulnerability tracked as CVE-2025-2783 (CVSS score: 8.3).
Google addressed the flaw later that month after Kaspersky reported in-the-wild exploitation in a campaign dubbed Operation ForumTroll targeting various Russian organizations.
“The initial attack vector was a phishing email containing a malicious link,” security researchers Stanislav Pyzhov and Vladislav Lunin said. “When the victim clicked the link, it triggered a one-click exploit (CVE-2025-2783), leading to the installation of the Trinper backdoor employed by TaxOff.”
The phishing email is said to have been disguised as an invitation to the Primakov Readings forum – the same lure detailed by Kaspersky – urging users to click on a link that led to a fake website hosting the exploit.
TaxOff is the name assigned to a hacking group that was first documented by the Russian cybersecurity company in late November 2024 as targeting domestic government agencies using legal and finance-related phishing emails to deliver Trinper.
Written in C++, the backdoor makes use of multithreading to capture victim host information, record keystrokes, gather files matching specific extensions (.doc, .xls, .ppt, .rtf, and .pdf), and establish a connection with a remote server to receive commands and exfiltrate the results of the execution.
The instructions sent from the command-and-control (C2) server extend the implant’s functionality, allowing it to read/write files, run commands using cmd.exe, launch a reverse shell, change directory, and shutdown itself.
“Multithreading provides a high degree of parallelism to hide the backdoor while retaining the ability to collect and exfiltrate data, install additional modules, and maintain communications with C2,” Lunin noted at the time.
Positive Technologies said its investigation into the mid-March 2025 intrusion led to the discovery of another attack dating back to October 2024 that also commenced with a phishing email, which purported to be an invitation to an international conference called “Security of the Union State in the modern world.”
The email message also contained a link, which downloaded a ZIP archive file containing a Windows shortcut that, in turn, launched a PowerShell command to ultimately serve a decoy document while also dropping a loader responsible for launching the Trinper backdoor by means of the open-source Donut loader. A variation of the attack has been found to swap out the Donut loader in favor of Cobalt Strike.
This attack chain, per the company, shares several tactical similarities with that of another hacking group tracked as Team46, raising the possibility that the two threat activity clusters are one and the same.
Interestingly, another set of phishing emails sent by the Team46 attackers a month before claimed to be from Moscow-based telecom operator Rostelecom, alerting recipients of supposed maintenance outages last year.
These emails included a ZIP archive, which embedded a shortcut that launched a PowerShell command to deploy a loader that had been previously used to deliver another backdoor in an attack targeting an unnamed Russian company in the rail freight industry.
The March 2024 intrusion, detailed by Doctor Web, is notable for the fact that one of the payloads weaponized a DLL hijacking vulnerability in the Yandex Browser (CVE-2024-6473, CVSS score: 8.4) as a zero-day to download and execute unspecified malware. It was resolved in version 24.7.1.380 released in September 2024.
“This group leverages zero-day exploits, which enables it to penetrate secure infrastructures more effectively,” the researchers said. “The group also creates and uses sophisticated malware, implying that it has a long-term strategy and intends to maintain persistence on the compromised systems for an extended period.”
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