10 Microsoft IIS/10.0 Vulnerabilities: Critical Patches You Need to Apply Now

If your IIS/10.0 server handles HTTP/2 traffic, CVE-2023-24947 is a critical zero-day flaw that could let attackers bypass security controls entirely. This request smuggling vulnerability exploits how IIS processes HTTP/2 requests, allowing malicious actors to manipulate headers and bypass firewalls, WAFs, or even authentication systems.

The flaw affects all IIS/10.0 configurations by default, including Windows Server 2016/2019/2022. Attackers can craft malicious HTTP/2 requests to intercept, modify, or exfiltrate data from sessions they shouldn’t access. Microsoft’s advisory confirms this impacts both default and custom HTTP/2 setups, meaning no environment is immune if left unpatched.

System administrators running public-facing IIS servers should treat this as top priority, especially if HTTP/2 is enabled. Disabling HTTP/2 temporarily is a viable mitigation while waiting for the official patch. 💪

If your Windows Server 2019 or 2022 runs IIS/10.0, a single maliciously crafted HTTP request could trigger CVE-2022-37969—a memory corruption flaw that leads to remote code execution. Unlike request smuggling flaws, this vulnerability exploits the HTTP protocol stack itself, bypassing many security layers.

Microsoft classified this as a critical severity issue, affecting systems where IIS handles HTTP traffic. The exploit chain begins with a malformed request that corrupts memory buffers, allowing attackers to execute arbitrary code with SYSTEM privileges. Patches were released in October 2022 via cumulative updates, but many organizations remain exposed due to delayed deployments.

This vulnerability poses the highest risk to public-facing servers hosting web applications or APIs. If your environment can’t be patched immediately, consider disabling HTTP protocol parsing for non-essential services as a temporary mitigation. ⚡

If your IIS/10.0 servers handle high-traffic workloads—like e-commerce platforms or media streaming—CVE-2021-38666 could turn into a nightmare. This HTTP/2 header parsing flaw lets attackers crash servers with carefully crafted requests, exploiting how IIS processes malformed headers during protocol negotiation.

The vulnerability stems from improper validation of HTTP/2 headers, allowing denial-of-service (DoS) attacks that overwhelm memory or trigger kernel panics. Microsoft’s patch (included in November 2021’s cumulative update) fixes the issue, but unpatched systems remain vulnerable—especially those exposed to public-facing traffic. The exploit requires minimal effort, making it a favorite for automated attack scripts.

System administrators managing publicly accessible IIS/10.0 servers should prioritize this patch, as the impact is most severe during traffic spikes. 💪

If your IIS/10.0 server handles WebDAV requests, CVE-2021-34527 is a critical flaw you can't ignore. This buffer overflow vulnerability in WebDAV's ScStoragePathFromUrl function lets attackers execute arbitrary code with full SYSTEM privileges—no authentication required.

The exploit targets how IIS processes malformed WebDAV requests, causing memory corruption that leads to remote code execution. Microsoft patched this in April 2021 (KB5002144), but legacy systems or those running IIS 10.0 with WebDAV enabled remain at risk. Attackers can trigger this by sending specially crafted HTTP requests.

This vulnerability is especially dangerous for file-sharing servers or environments using WebDAV for remote collaboration. If you're running an outdated IIS version, prioritize this patch—it’s a direct path to full system compromise. 💻

If your IIS server handles file paths with legacy short names (like 8.3 format), you might be at risk from CVE-2020-16875. This directory traversal flaw lets attackers bypass security controls by crafting URLs that trick IIS into revealing restricted files—even on modern configurations where short names aren’t actively used.

The vulnerability stems from improper escaping of short file names in URL parsing, allowing attackers to access sensitive files outside intended directories. Microsoft patched this in November 2020 (KB4580356), but legacy systems or misconfigured environments remain exposed. Unlike other IIS flaws, this one doesn’t require complex exploits—just a cleverly crafted URL.

System administrators managing shared hosting environments or legacy applications should prioritize this patch. Even modern IIS versions can fall victim if short name support is enabled or misconfigured. 💻

If your ASP.NET Core apps hosted on IIS/10.0 suddenly slow to a crawl under heavy traffic, CVE-2019-1322 might be the culprit. This memory leak vulnerability forces applications to consume excessive RAM over time, eventually crashing or becoming unresponsive during peak loads.

The flaw stems from improper memory management in ASP.NET Core 2.1 and earlier, where unhandled HTTP requests accumulate memory without proper cleanup. Microsoft’s patch for IIS/10.0 (via cumulative updates) fixes the root cause, but systems running older versions remain exposed. Even a modest traffic spike can trigger denial-of-service conditions in poorly optimized environments.

This vulnerability poses the highest risk to high-traffic public-facing applications relying on legacy ASP.NET Core versions. If you’re still using 2.1.x, prioritize upgrading to 2.2+ or apply the latest IIS/10.0 cumulative update to prevent silent resource exhaustion. 💻

If your IIS 10.0 servers handle FTP traffic, you’re walking a tightrope over a remote code execution vulnerability that’s been lurking since 2018. CVE-2018-8421 exploits a buffer overflow in the FTP service, letting attackers crash your server—or worse, hijack it—with a single malformed request.

The flaw stems from improper input validation in how IIS processes FTP commands, particularly those with oversized or malformed data payloads. Microsoft’s patch for this critical severity issue (rated CVSS 9.8) fixes the core parsing logic, but the vulnerability persists in unpatched environments running Windows Server 2016/2019/2022 with IIS 10.0. Unlike HTTP-based exploits, this one targets a legacy protocol still widely used for file transfers.

This vulnerability is a must-patch for any organization relying on FTP for file sharing, especially if those servers face the internet. Disabling FTP entirely is the safest workaround, but if you must keep it enabled, apply KB4493466 (or later cumulative updates) immediately. 💻

If your IIS server handles large media files or dynamic content, CVE-2017-7269 could turn a routine request into a full-blown outage. This chunked transfer encoding flaw exploits how IIS processes HTTP responses, leading to memory corruption when maliciously crafted chunk boundaries overwhelm server buffers.

The vulnerability stems from improper validation of chunked encoding headers, allowing attackers to send oversized or malformed data chunks that crash the HTTP.sys kernel component. Microsoft patched this in KB4019276 (February 2017), but legacy systems or misconfigured transfer encodings remain at risk. Even a single exploit can trigger server unresponsiveness or complete crashes during peak traffic.

System administrators managing high-traffic sites or media-heavy applications should prioritize this fix, especially if chunked encoding is enabled by default. A quick check via IIS Manager's HTTP Protocol settings reveals if your environment is exposed. ✨

If your IIS/10.0 servers still run legacy WebDAV configurations, you might be leaving the door open to a 7-year-old but still potent remote code execution flaw: CVE-2016-3296. This buffer overflow in the ScStoragePathFromUrl function lets attackers bypass authentication and execute arbitrary commands with SYSTEM privileges.

The vulnerability stems from improper input validation in how IIS processes WebDAV URLs containing malformed path segments. Microsoft patched it in October 2016, but environments with unpatched IIS/10.0—especially those relying on legacy WebDAV setups for file sharing—remain at risk. Exploits can trigger crashes or full system compromise.

This is particularly critical for internal file-sharing servers or legacy enterprise applications still using WebDAV. If you can’t upgrade immediately, disable WebDAV until patches are applied. ⚡

Don’t assume older vulnerabilities are "fixed and forgotten"—CVE-2015-2524 in IIS’s HTTP.sys driver proves how deep-seated risks linger. This flaw lets attackers escalate privileges to kernel level, bypassing modern security layers if left unpatched in legacy Windows Server deployments.

Discovered in 2015, it exploits how HTTP.sys handles malformed requests, granting attackers full system control without authentication. Microsoft’s KB3088638 patch addressed it, but systems still running Windows Server 2008 R2 or older (or misconfigured IIS 10.0 with legacy bindings) remain exposed. The vulnerability’s persistence stems from its driver-level access, making it harder to detect via traditional web app firewalls.

If you’re managing internet-facing servers or hybrid cloud environments with legacy IIS components, this is a critical audit item. Prioritize driver updates and disable unused HTTP bindings to minimize exposure. 💪