Microsoft IIS Flaw Enables Remote Code Execution by Unauthorized Attackers

A newly disclosed vulnerability in Internet Information Services (IIS) Inbox COM Objects could allow attackers to execute arbitrary code on affected systems.

Tracked as CVE-2025-59282, the flaw stems from a race condition and use-after-free scenario in shared memory components.

Microsoft assigned itself as the CNA and rated the issue as Important, with a CVSS 3.1 score of 7.0 (temporal 6.1) based on local attack vector, high complexity, no required privileges, and user interaction.

Race Condition in Inbox COM Objects

The vulnerability arises from concurrent execution on a global memory resource used by certain IIS COM objects. In a race condition (CWE-362), improper synchronization lets one thread free memory that another thread still uses (CWE-416), creating a window for use-after-free exploitation.

An attacker can craft a malicious file and trick a local user into opening it. If the race is won, arbitrary code runs with elevated trust on the same machine, potentially granting shell access or the ability to drop additional payloads.

• Attack requires precise timing to exploit the synchronization flaw.
• Involves both race condition and use-after-free vulnerabilities.
• Relies on user opening a specially crafted file.

Understanding these technical details helps defenders anticipate and recognize suspicious file executions.

Attack Complexity and Mitigation Strategies

Despite being labeled Remote Code Execution, exploitation is strictly local: an attacker must already have code execution capabilities on the target host or persuade a legitimate user to load a specially crafted component.

The CVSS vector string CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H underscores this nuance: the attack complexity is high, requiring precise timing to win the race, and user interaction is mandatory.

No known public exploit or widespread weaponization exists, and Microsoft assesses real-world exploitation as unlikely at present.

• Systems without IIS enabled remain unaffected.
• Disabling legacy COM object support reduces attack surface.
• Application whitelisting can prevent untrusted file execution.

Until an official patch is applied, these mitigations provide layered defenses against potential exploitation.

Microsoft’s Response and Recommendations

Microsoft released an official fix on October 14, 2025, within its regular security update cycle. All supported versions of Windows Server running IIS should install the update immediately to remediate CVE-2025-59282.

Organizations are encouraged to review their software inventory for IIS installations and confirm that inbox COM object features are disabled unless explicitly needed.

Regularly monitoring the Microsoft Support Lifecycle portal ensures that patches are applied promptly to maintain a hardened environment against coordinated vulnerability disclosures.

Staying current with security bulletins and reinforcing local security policies remains essential, as emerging vulnerabilities like this one continue to target underlying synchronization flaws in legacy components.

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