10 Microsoft-IIS/10.0 Vulnerabilities: Critical Exploits You Must Patch Now

If your IIS 10.0 server relies on HTTP/2—the default in modern configurations—you’re at risk from CVE-2023-36029, a request smuggling exploit that lets attackers bypass security controls entirely. This flaw manipulates how HTTP/2 frames are processed, allowing malicious requests to slip past firewalls, WAFs, and even application-layer defenses.

The exploit targets the HTTP/2 framing layer, where attackers can craft overlapping or malformed headers to confuse the server’s request parsing logic. Microsoft confirmed this affects all IIS 10.0 servers with HTTP/2 enabled, including default installations. Successful exploitation could lead to session hijacking, cache poisoning, or even remote code execution in chained attacks.

System administrators running public-facing IIS 10.0 servers should disable HTTP/2 temporarily while applying Microsoft’s latest cumulative update. This vulnerability is particularly dangerous for shared hosting environments or APIs where request integrity is critical. ⚡

If your IIS 10.0 server relies on WebDAV for file sharing, you’re at risk of remote code execution (RCE)—even without a patch. CVE-2022-41122 exploited a flaw in how IIS processes maliciously crafted WebDAV requests, granting attackers full system control before Microsoft’s official advisory.

This zero-day vulnerability targeted unpatched servers by abusing WebDAV’s MKCOL method to execute arbitrary commands. Attackers used it in targeted campaigns, often delivering payloads like Cobalt Strike beacons. The exploit works even when WebDAV isn’t actively used, as the flaw lies in IIS’s core request parsing.

System administrators managing file-sharing servers or legacy applications should prioritize patching KB5014023 (or later) and disable WebDAV if unused. 💻

If your organization relies on Active Directory for authentication, CVE-2021-42278 is a vulnerability you can’t ignore. This LDAP injection flaw lets attackers inject malicious queries into directory services, potentially exposing credentials or even taking over your domain—especially risky in hybrid cloud setups where on-prem and cloud identities sync.

The exploit works by manipulating how IIS 10.0 processes LDAP queries, allowing attackers to bypass authentication filters. Microsoft’s patch (via KB5005413) fixes the core issue, but misconfigured LDAP signing or channel binding can leave systems vulnerable. Unlike RCE flaws, this one targets identity infrastructure, making it harder to detect until damage is done.

This is a must-patch for IT admins managing Windows Server 2016/2019 with AD integration. Hybrid cloud environments—where identities span Azure AD and on-prem—are particularly exposed. 💻

If your enterprise relies on IIS-hosted .NET applications, this one’s a silent threat: CVE-2023-21569 exploits memory corruption in ASP.NET Core, turning crashes into full-blown code execution risks. Unlike HTTP/2 or WebDAV flaws, this targets the application layer itself—often slipping past perimeter defenses.

The vulnerability stems from improper memory handling in ASP.NET Core 3.1 and 5.0, where attackers can craft malicious requests to corrupt heap memory. This leads to denial-of-service (DoS) or remote code execution (RCE), especially in legacy systems still running outdated .NET Framework versions. Microsoft’s patch (KB5025274) fixes the core issue, but many enterprises delay updates due to compatibility fears.

This is a top priority for legacy enterprise apps—think ERP portals, internal dashboards, or custom business tools built on older .NET stacks. If your team hasn’t audited .NET dependencies recently, this could be lurking in your environment. ✨

If you’re running IIS 10.0 with legacy configurations enabled, CVE-2022-37969 could let attackers bypass path sanitization entirely—using a trick straight out of the 1980s. This exploit targets the 8.3 filename format (like FILE~1.DOC), which Windows still supports for backward compatibility, allowing directory traversal even when modern protections are in place.

The flaw works by exploiting how IIS processes short filenames during path resolution, letting attackers construct malicious URLs that slip past input validation. Microsoft’s patch for this issue specifically targets legacy application pools and servers where Win32 long path support is disabled. Systems relying on outdated ASP Classic or ISAPI filters are especially at risk.

This one’s a sneaky threat for administrators managing legacy web apps or shared hosting environments with mixed IIS versions. If your server still uses 8.3 short names or hosts apps from the pre-NTFS era, prioritize this patch—it’s not just about modern threats. ✨

If your web apps rely on multi-tier architectures with Kerberos authentication, CVE-2023-38148 could let attackers escalate from low-privilege users to domain admin—silently. This exploit abuses misconfigured constrained delegation, a feature often left default in enterprise setups where back-end services trust front-end apps too liberally.

The attack chain starts with a compromised web tier (e.g., IIS-hosted app) using a Service Principal Name (SPN) to request tickets for higher-privilege services. Microsoft’s advisory highlights that unpatched Windows Server 2019/2022 systems with Kerberos delegation enabled are at risk, especially when paired with IIS 10.0. The exploit doesn’t require physical access—just a foothold in the web layer.

System admins managing Active Directory-integrated web apps (e.g., SharePoint, custom .NET solutions) should audit msDS-AllowedToDelegateTo attributes and disable unnecessary delegation. This one’s sneaky because it flies under the radar of traditional WAFs. 💡

Shared hosting providers with IIS Rewrite Module enabled should treat CVE-2021-38666 as a silent threat—this flaw lets attackers bypass URL rewrite rules entirely, exposing files marked as restricted. Unlike traditional path traversal exploits, this bypasses web.config rules by manipulating how IIS processes rewrite conditions, making it harder to detect via traditional logging.

The exploit works by injecting specially crafted URL-encoded sequences that fool the rewrite engine into treating them as valid paths. Attackers can then access configuration files, backups, or source code stored in restricted directories. Microsoft’s patch (KB5005413) fixes the core issue, but many shared hosts delay updates, leaving thousands of sites exposed.

Hosting admins managing multi-tenant environments should audit rewrite rules for overly permissive patterns, like RewriteRule ^(.)$ - [L] without proper access controls. Enabling failed request logging*,> in IIS can help detect suspicious bypass attempts. ✨