CVE-2026-49793 is a Windows Resilient File System (ReFS) heap-based buffer overflow that can lead to remote code execution. Microsoft rates it High severity with a CVSS v3.1 base score of 7.8 and temporal score of 6.8. The vector is local attack only (AV:L), low attack complexity, low privileges required, and no user interaction, with high confidentiality, integrity, and availability impact. Microsoft lists the exploit status as not publicly disclosed and not exploited, with exploit code maturity unproven. Because the attack vector is local rather than network-based, enterprise exposure is lower than for remote network services, but it remains important on systems where untrusted local code or users are present.

Highlights:
- CVSS scores: Base 7.8 - Temporal 6.8
- Exploit status & code maturity: Publicly Disclosed: No; Exploited: No; Exploit Code Maturity: UNPROVEN
- Impact: Remote Code Execution with HIGH confidentiality, integrity, and availability impacts
- Exploitation likelihood: Exploitation Less Likely; vector context is LOCAL, LOW attack complexity, LOW privileges required, and NO user interaction
- Severity for enterprise: High technical severity, but real-world enterprise risk is reduced by the local-only vector; highest concern is on systems where local attacker access is possible
- Patch status: available

Affected systems:
- Windows 10 1607
- Windows 10 1809
- Windows 10 21H2
- Windows 10 22H2
- Windows 11 24H2
- Windows 11 25H2
- Windows 11 26H1
- Windows 11 unspecified
- Windows Server 2016
- Windows Server 2019
- Windows Server 2022
- Windows Server 2025