Defender For EndpointApplication · Microsoft
CVE-2026-21537
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedImproper control of generation of code ('code injection') in Microsoft Defender for Linux allows an unauthorized attacker to execute code over an adjacent network.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · moderate confidenceA code injection vulnerability in Microsoft Defender for Linux allows an adjacent network attacker to inject and execute arbitrary code. The flaw stems from improper control of code generation, likely in the antivirus's scanning or update mechanisms, enabling remote code execution without authentication but requiring network adjacency.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data
Defender For EndpointApplication
all versionsCVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Adjacent
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Verify Microsoft Defender for Endpoint is installed on LinuxRun command: rpm -qa | grep -i defender OR dpkg -l | grep -i mdatp OR which mdatpAffected if The command returns any mdatp or Defender package, indicating Defender for Endpoint is installed on Linux
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Confirm the Defender for Endpoint service is runningRun command: systemctl status mdatp OR ps aux | grep mdatpAffected if The service is active/running, meaning the vulnerable component is operational
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Check if real-time protection or scanning is enabledRun command: mdatp config real-time-protection-statistics get OR mdatp statusAffected if Real-time protection or antivirus scanning is enabled (the vulnerable code generation occurs in scanning mechanisms)
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Assess network exposure of the Defender serviceReview network listening ports: netstat -tlnp | grep mdatp OR ss -tlnp | grep mdatp. Check if Defender listens on non-loopback interfacesAffected if Defender is bound to accessible network interfaces, enabling adjacent attackers to reach the vulnerable component
If Microsoft Defender for Endpoint is installed and running on Linux with network accessibility, the environment is affected by CVE-2026-21537 since all versions are vulnerable.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataApply Microsoft security updates for Defender for Linux immediately. Until patched, minimize network exposure and restrict lateral movement from untrusted network segments.
Fix this in Defender For Endpoint
Scoped from the published advisory
- Consultation4.0 h
- Implementation2.0 h
- Testing4.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,392.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-21537 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-21537 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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