We use optional cookies to improve your experience on our websites, such as through social media connections, and to display personalized advertising based on your online activity. If you reject optional cookies, only cookies necessary to provide you the services will be used. You may change your selection by clicking “Manage Cookies” at the bottom of the page. Privacy Statement Third-Party Cookies AcceptRejectManage cookies MSRC  Customer Guidance  Security Update Guide  Vulnerabilities  CVE-2026-55011 Microsoft Defender Remote Code Execution Vulnerability New On this page  CVE-2026-55011  Subscribe RSS PowerShell  API  CSAF Security Vulnerability Released: Jul 14, 2026 Assigning CNA Microsoft CVE.org link CVE-2026-55011  Impact Remote Code Execution Max Severity Critical Weakness CWE-191: Integer Underflow (Wrap or Wraparound) CVSS Source Microsoft Vector String CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C Metrics CVSS:3.1 7.8 / 6.8  Base score metrics: 7.8 / Temporal score metrics: 6.8  Expand all  Collapse all Metric Value   Base score metrics(8) Attack Vector Local Attack Complexity Low Privileges Required None User Interaction Required Scope Unchanged Confidentiality High Integrity High Availability High   Temporal score metrics(3) Exploit Code Maturity Unproven Remediation Level Official Fix Report Confidence Confirmed Please see Common Vulnerability Scoring System for more information on the definition of these metrics. Executive Summary Integer underflow (wrap or wraparound) in Microsoft Defender allows an unauthorized attacker to execute code locally. Exploitability The following table provides an exploitability assessment for this vulnerability at the time of original publication. Publicly disclosed No Exploited No Exploitability assessment Exploitation Less Likely FAQ According to the CVSS metric, the attack vector is local (AV:L). Why does the CVE title indicate that this is a remote code execution? The word Remote in the title refers to the location of the attacker. This type of exploit is sometimes referred to as Arbitrary Code Execution (ACE). The attack itself is carried out locally. For example, when the score indicates that the Attack Vector is Local and User Interaction is Required, this could describe an exploit in which an attacker, through social engineering, convinces a victim to download and open a specially crafted file from a website which leads to a local attack on their computer. References Identification Last version of the Microsoft Malware Protection Engine affected by this vulnerability 1.1.26050.11 First version of the Microsoft Malware Protection Engine with this vulnerability addressed 1.1.26060.3008 See Manage Updates Baselines Microsoft Defender Antivirus for more information. Microsoft Defender is disabled in my environment, why are vulnerability scanners showing that I am vulnerable to this issue? Vulnerability scanners are looking for specific binaries and version numbers on devices. Microsoft Defender files are still on disk even when disabled. Systems that have disabled Microsoft Defender are not in an exploitable state. Why is no action required to install this update? In response to a constantly changing threat landscape, Microsoft frequently updates malware definitions and the Microsoft Malware Protection Engine. In order to be effective in helping protect against new and prevalent threats, antimalware software must be kept up to date with these updates in a timely manner. For enterprise deployments as well as end users, the default configuration in Microsoft antimalware software helps ensure that malware definitions and the Microsoft Malware Protection Engine are kept up to date automatically. Product documentation also recommends that products are configured for automatic updating. Best practices recommend that customers regularly verify whether software distribution, such as the automatic deployment of Microsoft Malware Protection Engine updates and malware definitions, is working as expected in their environment. How often are the Microsoft Malware Protection Engine and malware definitions updated? Microsoft typically releases an update for the Microsoft Malware Protection Engine once a month or as needed to protect against new threats. Microsoft also typically updates the malware definitions three times daily and can increase the frequency when needed. Depending on which Microsoft antimalware software is used and how it is configured, the software may search for engine and definition updates every day when connected to the Internet, up to multiple times daily. Customers can also choose to manually check for updates at any time. What is the Microsoft Malware Protection Engine? The Microsoft Malware Protection Engine, mpengine.dll, provides the scanning, detection, and cleaning capabilities for Microsoft antivirus and antispyware software. Windows Defender uses the Microsoft Malware Protection Engine. On which products is Defender installed and active by default? Defender runs on all supported version of Windows. Are there other products that use the Microsoft Malware Protection Engine? Yes, Microsoft System Center Endpoint Protection, Microsoft System Center 2012 R2 Endpoint Protection, Microsoft System Center 2012 Endpoint Protection and Microsoft Security Essentials. Does this update contain any additional security-related changes to functionality? Yes. In addition to the changes that are listed for this vulnerability, this update includes defense-in-depth updates to help improve security-related features. Acknowledgements Anonymous Microsoft recognizes the efforts of those in the security community who help us protect customers through coordinated vulnerability disclosure. See Acknowledgements for more information. Security Updates To determine the support lifecycle for your software, see the Microsoft Support Lifecycle. Release date Descending  Edit columns  Download  Filters  Product Family  Max Severity  Impact  Platform   Clear Release date  Product Platform Impact Max Severity Article Download Build Number Assigning CNA Title: Release date, Content: Jul 14, 2026 Microsoft Malware Protection Engine - Remote Code Execution Critical Title: Knowledge Base Articles for Microsoft Malware Protection Engine, Content:, 1 link Release Notes  Title: Download Security Update for Microsoft Malware Protection Engine, Content:, 1 link Security Update Title: Build numbers, Content: 1.1.26060.3008 Title: Assigning CNA, Content: Microsoft All results loaded Loaded all 1 rows Disclaimer The information provided in the Microsoft Knowledge Base is provided "as is" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply. Revisions version revisionDate description 1.0 Jul 14, 2026 Information published.  How satisfied are you with the MSRC Security Update Guide? Rating  Broken  Bad  Below average  Average  Great!  Your Privacy Choices Consumer Health Privacy Privacy & Cookies