Threat Research Center Threat Research Malware Malware Vidar Stealer Unmasked: Code Signing Abuse, Go Loaders and File Inflation 10 min read Related Products Advanced DNS Security Advanced URL Filtering Advanced WildFire Cloud-Delivered Security Services Prisma Browser Unit 42 Incident Response By: Bharath Nannaka Pranay Kumar Chhaparwal Published: July 7, 2026 Categories: Malware Threat Research Tags: AMSI Cryptocurrency DLL Sideloading Factory-v3 Malvertising X3D MINER Share Executive Summary In April 2026, Unit 42 researchers identified a financially motivated campaign delivering Vidar stealer and the XMRig cryptocurrency miner to consumer and small- and medium-sized business victims worldwide. Attackers lure victims via malvertising to pages for downloading files that impersonate cracked versions of copyright-protected software. Upon execution, the loader drops and runs both Vidar stealer and XMRig. Vidar stealer targets information like browser credentials, cookies and crypto wallets. XMRig mines Monero cryptocurrency. We assess the operator of the campaign to be a Vidar stealer malware-as-a-service (MaaS) affiliate involved in operations targeting victims in the U.S. and European Union. This article provides a technical analysis of the campaign. Palo Alto Networks customers are better protected from the threats discussed above through the following products and services: Cortex XDR and XSIAM Advanced WildFire Advanced URL Filtering and Advanced DNS Security Prisma Browser If you think you might have been compromised or have an urgent matter, contact the Unit 42 Incident Response team . Related Unit 42 Topics Vidar Stealer , Malware , Cryptocurrency , XMRig Attack Timeline Since its emergence, attackers have used Vidar stealer in multiple large-scale campaigns. We identified a notable spike in activity from mid-late April 2026, primarily targeting organizations in the U.S. and the EU. Figure 1 illustrates the timeline of the April 2026 campaign, which shows the number of Vidar stealer samples discovered each day. Figure 1. April 2026 campaign. Our investigation of this activity led to the discovery of loader binaries distributing both Vidar stealer and XMRig. Initial Access: Malvertising via Fake Software Cracks This group behind this campaign distributes loader binaries through malvertising , targeting victims who search for pirated or cracked versions of copyright-protected software. The filenames used in this campaign mimic cracked versions of popular copyright-protected programs as well as generic installers. The campaign delivers the malware in password-protected archives with a .bin extension in the filenames. This appears to be a deliberate choice to bypass email gateway scanning and to prevent automated sandbox detonation without the password. We initially discovered 43 of these loader binaries that deliver Vidar stealer and XMRig. Upon extraction and execution, the loader binary is signed with a certificate (subject CN=justwatch[.]com ), creating a false sense of legitimacy before any malicious activity begins. Our analysis of these loader samples indicates they use the Factory-v3 framework. Factory-v3/UpdateFactory Builder Factory-v3 has been described as a MaaS builder used for different families of stealer malware. All 43 samples we discovered from this campaign contain embedded Go build metadata identifying the Factory-v3 framework. The Factory-v3 builder's internal name of UpdateFactor is revealed in a developer/build machine path shown in the programming database (PDB) strings of the loader DLL files: C:\Users\Administrator\Desktop\UpdateFactory\compiler\1.25.9\go\src\runtime\cgo Figure 2 shows a diagram of information from the build machine metadata. Figure 2. Information from the build machine path. The builder generates a unique binary per build. For example, we observed 27 unique build UUIDs across 43 samples, defeating hash-based detection. The builder uses Go version 1.25.9 , a custom pre-release of tools for the Go programming language. Anti-forensic measures are consistent across all samples: The PE TimeDateStamp is zeroed No PE version info is present DLL imports are reduced to kernel32.dll only User-defined type names are obfuscated to a V###### pattern The same builder, toolchain and Authenticode certificate infrastructure underpin a concurrent Lumma stealer campaign. This indicates Factory-v3 is used as a service for multiple stealer affiliates. Rogue Authenticode Certificate All 43 loader samples carry an Authenticode signature fabricated to impersonate JustWatch GmbH, a legitimate German streaming guide service. JustWatch has not been compromised. The certificate is entirely fabricated using a self-signed root certificate authority (CA) that is not present in any public trust store, as shown below in Figure 3. Figure 3. Rogue certificate information. Because the certificate is not chained to a Microsoft-trusted root, Windows SmartScreen and Authenticode validation will flag the binary as untrusted. However, the visual presence of a recognizable brand name in the signature dialog is sufficient to deceive many victims into proceeding. Sample Clusters The 43 loader samples fall into four clusters, as Table 1 below shows. Cluster CPU Architecture File Type Frequency Count Role A x64 EXE 26 Go loader (file-inflated EXE) B x64 DLL 13 Fake MpClient.dll sideload C x86 EXE 3 Go loader 32-bit (shared with Lumma Stealer campaign) D x64 EXE 1 Vidar core payload Table 1. Sample clusters with filetype. Cluster B DLL variants export Windows Defender MpClient.dll API functions to enable DLL search-order hijacking ( MITRE ATT&CK® T1574.002 ). When a legitimate Windows Defender binary attempts to load MpClient.dll , the operating system locates the malicious copy first if it is placed in a higher-priority search path. The exported function names mimicked include MpAllocMemory, MpClientUtilExportFunctions, MpConfigOpen, MpFreeMemory and nine others. File-Size Inflation Loaders in Clusters A and C append hundreds of megabytes of null bytes after the last PE section, pushing the total file size to as high as 491 MB. Most automated sandbox environments enforce an upper file-size limit of 50-100 MB and silently skip oversized submissions, meaning the malware never executes in the analysis environment. The real malicious content in the largest observed sample is only 2.3 MB, and the remaining 489 MB is null byte padding. Defenders should ensure security tooling removes null byte padding before applying size limits, since the same sample compresses to approximately 2.4 MB. AMSI Bypass Static disassembly of the Vidar core payload sample (SHA256 hash: 7ed4a256e1d281cb4f194d13ff554fb280dafde0a67a18115ea038ea6c87d ) reveals an in-memory Antimalware Scan Interface (AMSI) bypass that executes before any stealer logic runs. The routine loads amsi.dll , resolves the AmsiScanBuffer variable and overwrites its first six bytes with a patch. This patch forces the function to return E_INVALIDARG , which might disable Windows AMSI for all subsequent script and code execution on the victim machine. Both the DLL name and function name are XOR-obfuscated with single-byte key 0x05 to evade static string scanning. Table 2 shows the encoded and decoded strings for these names. Encoded String XOR Key Decoded String dhvl+aii 0x05 amsi.dll DhvlVfdkGpcc\`w 0x05 AmsiScanBuffer Table 2. Encoded and decoded strings from the sample. Figure 4 below shows patched bytes written to the AmsiScanBuffer location ( 0x80070057 ). Figure 4. AMSI buffer bytes. The binary uses a second, longer obfuscation layer for larger data blobs. This layer is obfuscated by a 32-byte rotating XOR with the key 69946018ddda1058ce5c2a556c78a747838865c47074dcb165effb0840cb1cf5 applied to the Telegram bot token, Monero wallet address and mining pool hostname for the XMRig payload. Attack Chain Figure 5 shows that the attack chain begins with malvertising, luring victims into downloading a password-protected .bin archive disguised as a cracked version of a legitimate program. Figure 5. Execution chain X3D MINER/Vidar Stealer via Factory-v3. The loader extracted from the .bin archive exhibits the following features: It leverages the Factory-v3 Go framework It is signed with a fake JustWatch certificate It is padded with null bytes to reach a large file size of hundreds of MB to evade detection The malware employs anti-analysis techniques such as process enumeration, alongside an AMSI bypass where the AmsiScanBuffer function is patched to prevent detection by some types of security software. Subsequently, the malware drops multiple payloads including Vidar stealer and the XMRig cryptocurrency miner, while establishing persistence mechanisms through registry modifications and scheduled tasks. The next stage involves reconnaissance, as the malware gathers information about files, hardware IDs (HWID) and bypasses proxies. Vidar stealer then exfiltrates sensitive data such as credentials and cryptocurrency wallets, communicating with a command-and-control (C2) server at 136.243.203[.]109 . Simultaneously, XMRig begins mining Monero using the mining pool at pool.supportxmr[.]com . Finally, the attacker is notified of new activity via Telegram, with messages labeled " X3D MINER • NEW LOG ," ensuring the operator stays informed about successful infections and stolen data. This means the threat actor behind Vidar is deploying the X3D MINER XMRig package. Dynamic analysis of the Vidar core payload confirmed the following execution sequence: Geolocation beacon : GET request to ip-api[.]com/json resolves the victim's public IP address and country, which are embedded in the subsequent Telegram alert Payload drop : It drops MicrosoftUpdate.exe in the %TEMP% directory as part of the Vidar stealer component and it places the following files in %AppData%\Temp%AppData%\Temp MicrosoftEdgeUpdate.exe (the XMRig launcher) libuv-1.dll (an XMRig dependency) WinRing0x64.sys (an XMRig