Microsoft IIS Vulnerability Allows Unauthorized Attacker To execute Malicious Code

Microsoft has disclosed a critical remote code execution flaw in its Internet Information Services (IIS) platform, posing risks to organizations relying on Windows servers for web hosting.

Tracked as CVE-2025-59282, the vulnerability affects the Inbox COM Objects handling global memory, stemming from a race condition and use-after-free error.

Announced on October 14, 2025, it carries a CVSS 3.1 base score of 7.0, rated as “Important” by Microsoft.

While not yet exploited in the wild, security experts warn that its potential for arbitrary code execution could enable attackers to compromise server integrity, steal data, or pivot to broader network attacks.

The flaw arises during concurrent execution where shared resources lack proper synchronization, allowing an unauthorized attacker to manipulate memory states.

According to the CVE details, exploitation requires local access but can originate from a remote adversary who tricks a user into opening a malicious file.

No privileges are needed, though the high attack complexity demands winning a precise race condition, making it challenging yet feasible for skilled threat actors.

Microsoft IIS Vulnerability

At its core, CVE-2025-59282 exploits weaknesses in CWE-362 (race condition) and CWE-416 (use-after-free) within IIS’s COM object management.

When a user interacts with a crafted file, such as a specially malformed document or script, the vulnerability triggers improper memory handling.

This leads to a use-after-free scenario where freed memory is accessed concurrently, enabling code injection.

The CVSS vector string, CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H, highlights key factors: local attack vector, high complexity, required user interaction, and high impacts across confidentiality, integrity, and availability.

Microsoft clarifies that “remote” in the title refers to the attacker’s position, not the execution site, distinguishing it from fully remote exploits.

No proof-of-concept code has been publicly released, but researchers note similarities to past IIS memory issues, where attackers could escalate to system-level control.

Affected versions include Windows Server editions with IIS enabled, though Microsoft has not specified exact builds in initial advisories.

Successful exploitation could allow attackers to run arbitrary code with the privileges of the IIS process, often running as SYSTEM on misconfigured servers.

In enterprise environments, this might expose sensitive web applications, databases, or API endpoints to ransomware deployment, data exfiltration, or lateral movement.

For instance, a compromised IIS server in a corporate intranet could serve as an entry point for advanced persistent threats targeting financial or healthcare sectors.

Given the “Exploitation Unlikely” assessment from Microsoft’s MSRC, immediate threats remain low. However, the lack of patches at disclosure time urges urgent updates.

No indicators of compromise (IoCs) have been detailed yet, but monitoring for unusual COM object interactions or memory anomalies in IIS logs is advised.

Mitigations

The simplest defense is disabling IIS if unused, as unaffected systems face no risk. Microsoft recommends applying forthcoming patches via Windows Update and restricting file execution policies.

Enabling User Account Control (UAC) and auditing COM interactions can further harden defenses.

Security firm researchers, including acknowledgers Zhiniang Peng from HUST and R4nger from CyberKunLun, emphasize timely patching to prevent escalation.

As IIS powers millions of web servers, this vulnerability underscores the need for vigilant memory-safe coding in legacy components. Organizations should scan environments and review web server configurations promptly.

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