Russian APT28 Hackers Targeting 13 Nations in Ongoing Cyber Espionage Campaign

CVE-2023-23397 is an elevation of privilege vulnerability in Microsoft Outlook caused by improper input validation (CWE-20) combined with authentication bypass via spoofed authentication data on the channel (CWE-294), allowing an attacker to force Outlook to authenticate to an attacker-controlled SMB/WebDAV server. It is triggered when Outlook processes a crafted email or calendar object — for example a meeting or task reminder whose sound property points to an attacker-supplied UNC path — and requires no user interaction. That authentication exchange leaks the victim's NTLM credential hash, which the attacker can crack offline or relay to authenticate as the victim and access resources such as Exchange mailboxes, effectively escalating privileges. Affected software spans Microsoft 365 Apps, Microsoft Office (including the Long Term Servicing Channel), and Microsoft Outlook, which are deployed across enterprises, governments, and militaries worldwide. It is actively exploited in the wild — added to CISA's Known Exploited Vulnerabilities catalog on 2023-03-14 with a 97.4% EPSS — and Microsoft has warned of exploitation by Russia-aligned threat actors in campaigns against government and military mail servers, with patches shipped in Microsoft's March 2023 security updates.

Do: Apply Microsoft's March 2023 security updates to Microsoft 365 Apps, Office/LTSC, and Outlook immediately, per CISA's required action. As interim mitigation, enable Extended Protection for Authentication or add accounts to the Protected Users group to block the NTLM credential leak, and audit calendar and task reminder sound properties for UNC paths (Microsoft published an audit/cleanup script for this) while watching for unexpected outbound SMB/WebDAV connections from hosts running Outlook.

RARLAB WinRAR before 6.23 mishandles ZIP archives that contain a benign file (such as a JPG) alongside a folder with the same name, causing the folder's contents - which can include malicious executable files - to be processed when the user merely attempts to view the benign file. By sending a crafted ZIP archive, an attacker gains arbitrary code execution on the victim's machine with the user's privileges. Because the flaw is local (AV:L) and requires user interaction, risk is limited to Windows systems running an unpatched copy of WinRAR, while machines without the tool are unaffected. The bug was actively exploited in the wild from April through October 2023, including by government-backed actors (APT28), SideCopy attacks on Indian government entities, ransomware operations, and trading-account theft campaigns, and it was added to CISA's Known Exploited Vulnerabilities catalog on 2023-08-24.

Do: Upgrade all Windows systems running WinRAR to version 6.23 or later, which fixes this flaw; if patching is not immediately possible, treat ZIP files from untrusted sources with caution and check archives for duplicate file/folder names before opening. Given KEV listing with known ransomware use and public proof-of-concept exploits, hunt for compromise by reviewing whether unexpected executables or scripts ran when ZIP archives were opened, and apply vendor mitigations per CISA's required action or discontinue use if mitigations are unavailable.