Microsoft releases urgent Office patch. Russian
Vulnerabilities mentionedAll →
| CVE | Vulnerability | CVSS | EPSS | Flags | Affected | Exposure | Published |
|---|---|---|---|---|---|---|---|
| CVE-2026-21509 | Local Security Feature Bypass in Microsoft Office Under Active Exploitation CVE-2026-21509 is a security feature bypass in Microsoft Office caused by reliance on untrusted input when making a security decision (CWE-807): Office trusts attacker-controlled data when deciding whether a protection applies, allowing an unauthorized local attacker to bypass that security feature. Exploitation is local and requires user interaction (per the CVSS vector), most plausibly by getting a user to open a crafted file or document, and the flaw carries high confidentiality, integrity, and availability impact. Anyone running Microsoft Office, Microsoft 365 Apps, or Office Long Term Servicing Channel is in scope, giving the flaw a potential audience in the hundreds of millions of seats. The flaw is being actively exploited: it was added to CISA's Known Exploited Vulnerabilities catalog on 2026-01-26, Microsoft issued an emergency patch, and headlines attribute in-the-wild use to Russian state hackers targeting Ukrainian and EU organizations, including the maritime and transport sectors (a related APT28 campaign was tied to a separate Office/MSHTML 0-day, CVE-2026-21513). EPSS estimates a 72.6% probability of exploitation within the next 30 days (99th percentile). Do: Apply Microsoft's emergency Office update and the follow-on February 2026 Patch Tuesday fixes across Microsoft 365 Apps, Office, and Office LTSC, checking Microsoft's advisory for the exact affected builds since no version ranges are given in the source data. Given the KEV listing, federal agencies must patch per CISA BOD 22-01 timelines (or follow cloud-service guidance). Hunt for exploitation per vendor guidance — headlines report Russian state use against EU/Ukrainian and maritime/transport targets — and prioritize endpoints where users open untrusted files. | 7.8 | 73% | KEV |
| masshundreds of millions of users/devices (Office and Microsoft 365 Apps have a global installed base on the order of 10^8+ seats) |
Full article288 words · extracted from arstechnica.com · click to collapse
Russian-state hackers wasted no time exploiting a critical Microsoft Office vulnerability that allowed them to compromise the devices inside diplomatic, maritime, and transport organizations in more than half a dozen countries, researchers said Wednesday.
The threat group, tracked under names including APT28, Fancy Bear, Sednit, Forest Blizzard, and Sofacy, pounced on the vulnerability, tracked as CVE-2026-21509, less than 48 hours after Microsoft released an urgent, unscheduled security update late last month, the researchers said. After reverse-engineering the patch, group members wrote an advanced exploit that installed one of two never-before-seen backdoor implants.
Stealth, speed, and precision
The entire campaign was designed to make the compromise undetectable to endpoint protection. Besides being novel, the exploits and payloads were encrypted and ran in memory, making their malice hard to spot. The initial infection vector came from previously compromised government accounts from multiple countries and were likely familiar to the targeted email holders. Command and control channels were hosted in legitimate cloud services that are typically allow-listed inside sensitive networks.
“The use of CVE-2026-21509 demonstrates how quickly state-aligned actors can weaponize new vulnerabilities, shrinking the window for defenders to patch critical systems,” the researchers, with security firm Trellix, wrote. “The campaign’s modular infection chain—from initial phish to in-memory backdoor to secondary implants was carefully designed to leverage trusted channels (HTTPS to cloud services, legitimate email flows) and fileless techniques to hide in plain sight.”
The 72-hour spear phishing campaign began January 28 and delivered at least 29 distinct email lures to organizations in nine countries, primarily in Eastern Europe. Trellix named eight of them: Poland, Slovenia, Turkey, Greece, the UAE, Ukraine, Romania, and Bolivia. Organizations targeted were defense ministries (40 percent), transportation/logistics operators (35 percent), and diplomatic entities (25 percent).
Text extracted automatically; images, tables and formatting may be missing. Original: https://arstechnica.com/security/2026/02/russian-state-hackers-exploit-office-vulnerability-to-infect-computers/