CVE-2019-1253

CVE-2019-1253 is an elevation of privilege vulnerability in the Windows AppX Deployment Server, which improperly handles junctions (reparse-point links, mapped to CWE-59), allowing file operations to be redirected to attacker-controlled locations. Exploitation is local: an attacker must first gain low-privileged code execution on the victim system, then abuse the flawed junction handling to escalate privileges. A successful attack yields elevated (administrative/SYSTEM-level) rights with high impact on confidentiality, integrity, and availability, reflected in the CVSS 3.1 score of 7.8. Affected systems are Windows 10 versions 1703, 1709, 1803, 1809, and 1903, and Windows Server 1803, 1903, and 2019. The flaw is being exploited in the wild — CISA added it to the Known Exploited Vulnerabilities catalog on 2022-03-15 with confirmed ransomware use — and EPSS puts the probability of exploitation in the next 30 days at 11.6% (96th percentile).

What to do: Apply Microsoft's security updates per vendor instructions immediately — patching is a CISA KEV required action and the flaw has confirmed ransomware use, so prioritize endpoints and servers. Because the affected builds (Windows 10 1703–1903 and Windows Server 1803/1903/2019) are legacy, verify each host is on a servicing channel still receiving the update or migrate to a supported build. Since exploitation requires prior low-privileged code execution, pair patching with endpoint detection coverage to catch initial-access activity before the privilege escalation step.