Security Affairs newsletter Round 562 by Pierluigi Paganini

A path traversal flaw (CWE-35) in the Windows version of WinRAR allows attackers to achieve arbitrary code execution by delivering a specially crafted archive file that writes outside the expected location when it is opened or processed. Because the CVSS 4.0 vector indicates a local attack requiring user interaction, victims are typically infected by extracting or previewing a malicious archive received via phishing, a malicious download, or another delivery channel. A successful attacker gains the privileges of the user running WinRAR, providing an initial foothold that has been used for both espionage and ransomware operations. Anyone running the Windows version of WinRAR — one of the most widely deployed Windows desktop utilities — is affected, and CPE data additionally lists dtSearch as an affected vendor. Exploitation is confirmed in the wild by nation-state actors (e.g., the China-linked Amaranth-Dragon group per related reporting) and criminal actors including ransomware operators; the flaw was added to CISA's Known Exploited Vulnerabilities catalog on 2025-08-12 and carries a near-maximal 94.6% EPSS score.

Do: Update WinRAR to the latest patched release from RARLAB on all Windows endpoints, prioritizing remediation per CISA KEV and BOD 22-01 requirements, and verify that dtSearch deployments bundling the affected component are also updated. Because exploitation requires a user to open or extract a crafted archive, warn users to treat unexpected archive files delivered by email or download with suspicion. Given confirmed ransomware use, hunt across user workstations — not just exposed servers — for suspicious archive-based infections and confirm the patched WinRAR version is installed.

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.