A Ghostwriter campaign using a new variant of PicassoLoader targets opposition activists in Belarus, and Ukrainian military and government organizations.SentinelLABS observed a new Ghostwriter campaign targeting Belarusian opposition activists and Ukrainian military and government entities with a new variant of PicassoLoader. The campaign has been active since late 2024, threat actors used weaponized Microsoft Excel documents as lures.The researchers believe the campaign is still ongoing, SentinelLABS states that the attacks are an extension of the long-running Ghostwriter campaign.The threat actor Ghostwriter (aka UNC1151, UAC-0057) is linked to the government of Belarus. In August 2020, security experts from FireEye uncovered a disinformation campaign aimed at discrediting NATO by spreading fake news content on compromised news websites. According to FireEye, the campaign tracked as GhostWriter, has been ongoing since at least March 2017 and is aligned with Russian security interests.The attack chain analyzed by SentinelLabs starts with a Google Drive link in a phishing email from a sender named “Vladimir Nikiforech.” It led to a RAR archive containing a malicious Excel workbook named “Political prisoners (across courts of Minsk).xls.” This marks a shift in Ghostwriter’s targeting, now aimed at Belarusian opposition. The attack, likely tied to Belarus’ Jan 26, 2025 election, used an obfuscated VBA macro to execute malicious code.Upon execution, the macro drops Realtek(r)Audio.dll in %Temp%, launching it via regsvr32.exe to execute a .NET assembly. The DLL is obfuscated with ConfuserEx and contains a stripped-down PicassoDownloader variant, linked to Ghostwriter. It decrypts additional code in memory and modifies its PE header for evasion.“As a part of application protection provided by the obfuscator, the Downloader creates a copy of itself in memory, and then modifies it. It does so by decrypting additional code of the assembly. It also uses a clever evasion technique, altering its own PE header in memory and breaking internal links to the .NET assembly. This makes it impossible for security products to parse it as a .NET module.” reads the report published by SentinelLABS. “The temp.xlsx decoy file is immediately opened in Excel in an attempt to make the victim believe that it contains the original content of the политзаключенные (по судам минска).xls file.”The decoy Excel file is shown while additional payloads download in the background. In past attacks, the nation-state actors used this method to deploy the post-exploitation tool Cobalt Strike, while now the malicious code delivers Ukraine-themed lures. SentinelOne found weaponized Excel files retrieving second-stage malware via steganography, hiding it in a JPG image from sciencealert[.]shop. The researchers noticed that the URLs are now inactive.The attack attribution is based on the use of PicassoLoader, a downloader toolkit linked to Ghostwriter. In 2024, the APT group deployed Excel workbooks with Macropack-obfuscated VBA macros and .NET downloaders obfuscated with ConfuserEx. This variant appears to be a simplified version of PicassoLoader.“The Ghostwriter threat actor has been consistently active in the past years and continues its attempts to compromise targets aligned with the interests of Belarus and its closest ally, Russia. It has mounted multiple attacks reported by CERT UA and other security researchers throughout 2024. While Belarus doesn’t actively participate in military campaigns in the war in Ukraine, cyber threat actors associated with it appear to have no reservation about conducting cyberespionage operations against Ukrainian targets.” concludes the report. “The campaign described in this publication also serves as confirmation that Ghostwriter is closely tied with the interests of the Belarusian government waging an aggressive pursuit of its opposition and organizations associated with it.”Follow me on Twitter: @securityaffairs and Facebook and MastodonPierluigi Paganini(SecurityAffairs – hacking, PicassoLoader)