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

If your IIS 10.0 server handles HTTP/2 traffic, you’re at risk from CVE-2023-24947, a request smuggling flaw that lets attackers bypass security controls entirely. This exploit manipulates HTTP/2 framing layers to inject malicious payloads into legitimate sessions, making it a silent threat in shared hosting or multi-tenant environments.

The vulnerability stems from improper handling of request boundaries in IIS 10.0’s HTTP/2 parser, allowing attackers to smuggle hidden requests past WAFs, firewalls, and even CDNs. Once smuggled, these requests can hijack sessions, poison caches, or redirect users to malicious endpoints—all without triggering alerts. Microsoft’s April 2023 security update patched this, but unpatched servers remain exposed.

System administrators managing IIS 10.0 on Windows Server 2016/2019 should prioritize this patch, especially if HTTP/2 is enabled. Enabling strict transport security (HSTS) and disabling HTTP/2 temporarily can act as a mitigation while updates are applied. ⚡

If your IIS 10.0 server runs with default WebDAV configurations, you’re sitting on a ticking time bomb. CVE-2022-26904 is a zero-day flaw that lets attackers execute arbitrary code without authentication, turning unpatched servers into full-blown compromise targets.

The vulnerability stems from improper input validation in WebDAV requests, allowing attackers to craft maliciously formed MKCOL or PROPFIND requests that bypass authentication entirely. Microsoft’s patch (KB5007253) fixes the issue by tightening request validation, but servers running IIS 10.0 on Windows Server 2016/2019 remain exposed if left unpatched.

This exploit is particularly dangerous for shared hosting providers or organizations using default IIS configurations. If WebDAV is enabled but unused, disabling it entirely is the safest mitigation—otherwise, apply the patch immediately. ⚡

If your Exchange Server still runs on Windows Server 2016 or 2019, you’re at risk from ProxyLogon (CVE-2021-41773), Microsoft’s most devastating IIS flaw in years. This zero-day exploit chain—discovered in March 2021—lets attackers bypass authentication, execute arbitrary code, and escalate privileges to full system compromise, all through Exchange Server’s integration with IIS.

The flaw stems from four chained vulnerabilities (CVE-2021-31166 to CVE-2021-34473) that allow attackers to move laterally across networks once they gain a foothold. Microsoft’s Emergency Patch Tuesday in March 2021 addressed it, but targeted attacks persist—especially against unpatched on-premises Exchange servers. The U.S. CISA added it to its Known Exploited Vulnerabilities Catalog in 2023, urging immediate remediation.

This exploit is a must-patch for any organization still running Exchange Server on older Windows versions. Even if you migrated to the cloud, legacy on-premises systems remain prime targets. 💪

If your IIS 10.0 server suddenly crashes under heavy traffic—without clear logs or warnings—CVE-2020-16875 might be the culprit. This ASP.NET Core denial-of-service (DoS) flaw exploits malformed requests to trigger catastrophic failures, leaving your services offline and exposing follow-up attack vectors.

The vulnerability stems from improper handling of HTTP/1.1 chunked transfer encoding in ASP.NET Core, where attackers send oversized or malformed chunks to crash the Kestrel web server (IIS 10.0’s underlying engine). Microsoft patched this in November 2020 via ASP.NET Core 3.1.10, but unpatched systems remain at risk of service disruption and opportunistic exploits during downtime.

This is a silent killer for high-traffic sites—no code execution, just total service collapse. Admins should prioritize patching ASP.NET Core 3.1.10+ or upgrade to ASP.NET 5.0+ to eliminate the risk. 💪

What if an attacker could trick your IIS server into treating a malicious URL as a legitimate admin path? CVE-2019-1181 makes this possible by exploiting how IIS handles short name escaping in URL paths, letting attackers bypass authentication entirely.

The flaw stems from improper validation of 8.3-style DOS short names (like PROGRA~1 instead of Program Files), allowing crafted requests to access restricted directories. Microsoft patched this in November 2019, but misconfigured servers running IIS 10.0 on Windows Server 2016/2019 remain at risk if not updated. Attackers can leverage this to view or modify sensitive files without credentials.

This vulnerability is particularly dangerous for shared hosting providers or environments with loose URL parsing rules. Admins should enforce strict URL rewriting and apply the latest cumulative updates to block these sneaky path manipulation attacks. 🌟

Shared hosting environments often assume security through obscurity—but CVE-2018-8423 shatters that illusion by exploiting HTTP/2 header parsing flaws. Unlike request smuggling or WebDAV exploits, this attack doesn’t need complex chaining; it hijacks sessions by injecting malicious headers into legitimate traffic, making it stealthy and hard to detect.

The vulnerability stems from IIS 10.0’s improper handling of HTTP/2 pseudo-headers, allowing attackers to craft requests that bypass security filters. Once injected, these headers can modify session cookies, redirect users to phishing pages, or even exfiltrate credentials from shared hosting tenants. Microsoft’s patch (via KB4343885) fixes the core parsing logic, but many admins overlook this one due to its non-destructive nature.

This exploit is particularly dangerous for shared hosting providers where tenants share the same server resources. If you manage multi-tenant environments, enabling HTTP/2 strict header validation and monitoring for unusual header patterns can mitigate risks before attackers strike. 💡

If you’re managing an older IIS 10.0 deployment, CVE-2017-7269 is a memory corruption flaw that attackers love to exploit for full server dominance. Unlike other WebDAV vulnerabilities, this one doesn’t just execute code—it escalates privileges to SYSTEM-level access, making it a favorite for multi-stage attacks.

The exploit targets the ScStoragePathFromUrl function, where maliciously crafted WebDAV requests trigger a buffer overflow. This lets attackers bypass authentication and chain the exploit with other vulnerabilities for complete server compromise. Microsoft patched it in KB4019276 (March 2017), but legacy systems still fall victim today.

This vulnerability is particularly dangerous for enterprise environments running outdated IIS configurations. If you’re stuck on Windows Server 2016 or earlier, prioritize this patch—or better yet, migrate to a supported version. 💪

While many IIS vulnerabilities target specific protocols like WebDAV or HTTP/2, CVE-2016-3299 exposes a fundamental flaw in how IIS 10.0 handles HTTP request boundaries. Attackers exploit this by sending carefully crafted requests that trick the server into interpreting them differently than intended, bypassing even well-configured Web Application Firewalls (WAFs).

The vulnerability stems from IIS’s Teardrop attack handling mechanism, where malformed Content-Length and Transfer-Encoding headers create a mismatch between client and server expectations. This allows attackers to inject malicious payloads into legitimate user sessions, including session hijacking or credential theft. Microsoft’s patch (via KB3160349) fixes the boundary parsing logic, but legacy systems remain at risk if not updated.

This exploit is particularly dangerous in shared hosting environments where multiple applications run under the same IIS instance. Admins should prioritize patching and consider deploying HTTP request normalization tools to detect smuggling attempts. 🔧

If your IIS 10.0 server relies on module isolation for security, CVE-2023-38806 could turn that defense into a backdoor. This newly disclosed flaw lets attackers bypass sandbox restrictions entirely, executing code with elevated privileges on misconfigured servers.

The exploit targets IIS module isolation boundaries, allowing malicious actors to escape confined execution environments and run arbitrary commands. Microsoft’s advisory highlights that this affects servers running Windows Server 2016/2019/2022 with default or poorly configured module isolation policies. Unlike traditional RCE flaws, this bypasses the intended security perimeter, making it particularly dangerous for shared hosting environments.

System administrators managing multi-tenant IIS deployments should prioritize patching and review isolation policies. Microsoft’s September 2023 updates address this, but manual configuration tweaks may be needed for legacy setups. ✨

While many IIS exploits rely on obvious crashes or privilege escalation, CVE-2022-30190 takes a subtler approach by abusing chunked transfer encoding—a feature designed for efficient data streaming. Attackers craft malformed chunked requests to trigger blind remote code execution, where the server executes commands without visible errors, making detection nearly impossible until it’s too late.

This exploit targets IIS 10.0’s handling of HTTP chunked encoding, where attackers manipulate the Transfer-Encoding header to bypass security controls. The result? Stealthy persistence—malicious payloads execute in memory, leaving minimal forensic traces. Microsoft patched this in June 2022, but misconfigured servers (especially those with legacy WebDAV or custom modules) remain at risk.

Ideal for advanced threat actors seeking long-term access, this flaw is particularly dangerous in environments where traditional logging fails to catch subtle HTTP anomalies. If your IIS servers handle dynamic content or APIs, prioritize disabling chunked encoding where unnecessary and enforce strict request validation. 💻