Integer overflow or wraparound in Microsoft Defender allows an unauthorized attacker to execute code locally.
In plain language
Written by AI from the record
CVE-2026-55012 is a Microsoft Defender bug that can let an attacker run arbitrary code on your machine if they can get a victim to interact with it; small businesses using Microsoft Malware Protection Engine should update because the fix is available.
CVE-2026-55012 is an integer overflow in Microsoft Malware Protection Engine that can lead to local arbitrary code execution; it is triggered via a local interaction with no required authentication.
If you're affected
Full endpoint compromise
Malware installation possible
Data theft from affected host
Operations disrupted
What is it
Think of Microsoft Malware Protection Engine as part of the guardrails that monitor and protect your computer. This bug is like a math mistake in how that component handles certain values—under the right local situation, a bad actor could potentially trick the guardrails into running attacker-controlled code. The result could be complete takeover of the affected computer.
Who is affected
This matters if your business endpoints run Microsoft Malware Protection Engine as part of Microsoft Defender. It’s not something that requires a login to trigger, but the bug does require user interaction and is described as a local attack, so it’s most relevant when an attacker can get someone to open or interact with something on the machine. Because “reachable in default config” is unknown, treat it as a risk when the vulnerable component is reachable and an attacker can induce the required user interaction on the host.
How urgent is it
This is a RED issue because it could allow arbitrary code execution on an endpoint, which is the kind of flaw attackers look for to fully compromise a machine. Even though exploitation in the press isn’t clearly documented with dates and there’s no public exploit code on record, the availability of a fixed version means you can reduce exposure immediately. Prioritize patching on all systems that run Microsoft Malware Protection Engine.
What to do — in detail
Inventory affected systems
Identify which devices have Microsoft Malware Protection Engine installed/active (typically as part of Microsoft Defender). Focus on every endpoint your users directly interact with.
Confirm the current version
On each device, determine the running Microsoft Malware Protection Engine version.
Compare it against the fixed version: 1.1.26060.3008.
Determine whether you are affected
If the device’s Microsoft Malware Protection Engine version is older than 1.1.26060.3008, it is considered affected and you should upgrade.
If it is already 1.1.26060.3008 or later, you should treat it as not affected for this CVE.
Upgrade to the fixed version
Upgrade Microsoft Malware Protection Engine to 1.1.26060.3008.
After upgrade, re-check the version to ensure the fixed version is actually active.
Temporary workaround if you can’t patch quickly
Because this requires user interaction and is local, reduce opportunities for attackers to induce interaction on those endpoints: tighten controls around opening unknown files/attachments, restrict risky application behaviors where your environment supports it, and ensure users follow safe browsing/downloading practices.
Also prioritize patching those endpoints first (machines exposed to the most untrusted input, such as email-heavy roles).
What to monitor after updating
Look for unusual local process creation or unexpected new executables shortly after user interactions (especially on endpoints you upgraded last).
If your organization has endpoint detection logs, verify that there are no suspicious alerts tied to Microsoft Defender/Malware Protection Engine activity around the timeframe.
KEV / deadlines
This CVE is not listed in CISA KEV, so no CISA-specific due date is provided by the findings.
Confirm completion
Provide a completion report: device list + pre-upgrade version + post-upgrade version results.
Technical context
Severity is high (CVSS 7.8) with local attack characteristics: it requires user interaction and does not require authentication. The core weakness is an integer overflow (CWE-122; also associated with incorrect handling such as CWE-190) in Microsoft Malware Protection Engine, which can be leveraged to achieve local arbitrary code execution. There is no indication from the provided findings that this CVE is listed in CISA KEV, and the press/exploitation findings do not provide clear dated evidence of in-the-wild exploitation; no public exploit code was found in the findings. The practical takeaway is that patching to the fixed Microsoft Malware Protection Engine version is the most reliable mitigation because the vulnerability targets code execution on the endpoint itself. Fix availability is confirmed: 1.1.26060.3008.
This is a general assessment based on public vulnerability data. It does not account for your specific infrastructure — when in doubt, consult a security specialist.
