Fancy Bear Exploits Microsoft RTF Zero-Day CVE-2026-21509 in Operation Neusploit
Fancy Bear (APT28) has been attributed with high confidence to Operation Neusploit, a campaign targeting users in Central and Eastern Europe by weaponizing CVE-2026-21509, a Microsoft RTF parsing zero-day that enables arbitrary code execution via specially crafted RTF documents. Reported lures were written in multiple languages (including English, Romanian, Slovak, and Ukrainian) and targeted victims in Ukraine, Slovakia, and Romania. Microsoft issued an out-of-band patch for CVE-2026-21509 on January 26, 2026, with in-the-wild exploitation observed shortly after.
Post-exploitation activity was described as a multi-stage chain that retrieves a malicious dropper DLL from attacker infrastructure and then deploys different payload paths, including MiniDoor (focused on Outlook email theft/exfiltration) and PixyNetLoader, which ultimately leads to a Covenant Grunt implant for command-and-control. The campaign also uses evasion and targeting controls, including region-restricted payload delivery (e.g., only serving malicious DLLs to requests from targeted geographies and specific User-Agent patterns) and persistence techniques such as COM hijacking, plus additional tradecraft like steganography in PNG files and shellcode loading to execute the final implant.
Timeline
Feb 9, 2026
Researchers document two Neusploit infection chains
Analysis of Operation Neusploit identified two distinct post-exploitation paths: one deploying MiniDoor to exfiltrate Outlook email via a malicious VBA project, and another deploying PixyNetLoader. The latter used COM hijacking, DLL proxying, PNG steganography, and shellcode loading to execute a Covenant Grunt implant communicating over the Filen API.
Jan 29, 2026
Operation Neusploit targets Central and Eastern Europe
Operation Neusploit used spear-phishing lures in English, Romanian, Slovak, and Ukrainian to target users, especially in Ukraine, Slovakia, and Romania. After exploitation, victims received tailored payloads through actor-controlled infrastructure using geo- and user-agent filtering.
Jan 29, 2026
In-the-wild exploitation of CVE-2026-21509 is observed
By January 29, 2026, active exploitation of CVE-2026-21509 had been observed in the wild. The campaigns were attributed with high confidence to Fancy Bear/APT28 and targeted users in Central and Eastern Europe.
Jan 28, 2026
FBI seizes RAMP cybercrime forum domains
In late January 2026, the FBI seized the Russian-language cybercrime forum RAMP. Authorities took over both its clearnet and Tor domains and replaced them with seizure notices.
Jan 26, 2026
Microsoft releases out-of-band patch for CVE-2026-21509
Microsoft issued an out-of-band patch for the zero-day CVE-2026-21509 on January 26, 2026. The flaw was being weaponized in malicious Microsoft RTF files to enable arbitrary code execution.
Jun 1, 2025
KTA529 allegedly hijacks Notepad++ update infrastructure
According to the SecuritySenses briefing, actor KTA529 compromised Notepad++ hosting infrastructure from June through December 2025 and used the access to hijack update traffic. The activity allegedly delivered a previously undocumented backdoor named CHRYSALIS.
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APT28 Exploits Microsoft Office RTF Zero-Day (CVE-2026-21509) in Operation Neusploit
**APT28** (Russia-linked) has been observed exploiting a **Microsoft Office RTF zero-day, `CVE-2026-21509`**, in a campaign dubbed **Operation Neusploit** targeting organizations in **Central and Eastern Europe** (including **Ukraine, Slovakia, and Romania**). The intrusion chain begins with **socially engineered emails** delivering **weaponized RTF documents**; opening the file triggers code execution and downloads a malicious **dropper DLL** from attacker-controlled infrastructure, enabling follow-on payload deployment and persistence. Technical analysis describes **two dropper variants** that deploy different components, including **MiniDoor**, a malicious **Microsoft Outlook VBA** project designed to **steal and forward emails**. Observed behaviors include writing the VBA payload to `%appdata%\Microsoft\Outlook\VbaProject.OTM`, creating a mutex (`adjgfenkbe`), and modifying Windows Registry settings to **weaken Outlook security** so the malicious project loads automatically at Outlook startup; string decryption uses XOR routines (including a hardcoded `0x3a` key and a rolling XOR key). Reporting attributes the activity to APT28 based on TTP overlaps and notes exploitation was seen **in the wild** shortly after Microsoft issued an emergency fix.
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