Description

Microsoft is aware of an elevation of privilege in the Microsoft Malware Protection Engine in Microsoft Defender publicly referred to as "ShieldBreak ". We are working to provide a high quality security update that addresses this vulnerability. We will provide information in this CVE when the update is available.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "7.8",
  "pubDate": "2026-08-14T22:17:06.810Z",
  "pubdate": "2026-08-14T22:17:06.810Z",
  "executiveSummary": "Microsoft is addressing a publicly disclosed elevation of privilege vulnerability affecting the Microsoft Malware Protection Engine within Microsoft Defender, designated with the identifier \"ShieldBreak \".\nThis vulnerability allows an unprivileged local attacker or a process running under restricted security contexts to escalate privileges on targeted Windows systems.\nThe security flaw resides directly in the core scanning and parsing components of the affected antimalware engine, which typically operates with elevated system-level privileges to inspect and remediate files.\nSuccessful exploitation of this vulnerability could grant an attacker higher-level privileges, potentially compromising the integrity and security of the entire operating system.\nThe risk implication is severe, as the Microsoft Malware Protection Engine processes untrusted files automatically during routine system scans, real-time protection monitoring, or definition updates.\nWhile specific exploitation requirements and attack vectors are presently restricted pending the release of official security updates, vulnerabilities of this class typically involve parsing malformed input files designed to trigger memory corruption or logic errors within the parsing engine.",
  "technicalDetails": "The vulnerability exists within the Microsoft Malware Protection Engine, specifically inside the proprietary file parsing and scanning subsystems utilized by Microsoft Defender.\nThe root cause stems from improper handling of specially crafted, malicious input data processed by the engine, which can lead to memory corruption, insecure object handling, or logic flaws during file inspection.\nBecause the Microsoft Malware Protection Engine executes as a privileged service within the operating system architecture, any successful state manipulation or arbitrary code execution achieved within the engine context can be leveraged to achieve an elevation of privilege.\nThe attack flow typically begins when a threat actor places a specially crafted payload or malformed file onto the local filesystem where it will be automatically ingested and parsed by the scanning engine during scheduled scans, real-time file access monitoring, or archive extraction routines.\nUpon ingestion, the vulnerable parsing component attempts to process the malformed structure without adequate boundary checks or input sanitization, triggering the underlying flaw.\nAuthentication and privilege requirements for initial execution are minimal; a local user with restricted access can stage the malicious file in a directory monitored by the engine or trigger a scan via standard system interactions.\nNetwork exposure is generally not required for initial exploitation if local file vectors are utilized, although remote vectors could theoretically apply depending on how untrusted files are synchronized or downloaded onto the endpoint.\nPost-exploitation impact includes the potential execution of arbitrary code with the elevated privileges of the antimalware service account, allowing the attacker to bypass local security controls, modify system configurations, install persistent backdoors, or compromise additional system components."
}