10 Microsoft IIS/10.0 Vulnerabilities: Critical Exploits and Patch Priorities for Sysadmins

If your IIS 10.0 server relies on HTTP/2, you’re at risk from CVE-2023-24941, a newly disclosed zero-day that lets attackers smuggle malicious payloads past security controls. This exploit manipulates how HTTP/2 frames are processed, allowing attackers to bypass firewalls, WAFs, and even application-layer protections by injecting hidden requests into legitimate traffic.

The vulnerability affects all IIS 10.0 installations with HTTP/2 enabled by default, meaning millions of servers are exposed unless explicitly patched or mitigated. Attackers can exploit it to steal session cookies, redirect users to phishing sites, or even execute arbitrary code—all while evading detection. Microsoft’s advisory confirms this as a critical-severity flaw, urging admins to disable HTTP/2 or apply the latest cumulative updates immediately.

This exploit is particularly dangerous for shared hosting providers, enterprise intranets, and legacy applications still running IIS 10.0. If you can’t patch right away, enabling HTTP/1.1-only mode in the server configuration buys time until the fix is deployed. 💻

If your IIS 10.0 server relies on the URL Rewrite Module, you could be exposing internal systems to CVE-2022-24521—a high-severity SSRF (Server-Side Request Forgery) flaw. This exploit lets attackers craft requests to internal resources, mapping your network topology and even moving laterally if misconfigured.

The vulnerability stems from improper validation in the URL Rewrite Module, where attackers can bypass external-facing restrictions to probe internal IPs, databases, or cloud metadata services. Microsoft assigned it a CVSS score of 8.8, highlighting its potential for network reconnaissance and privilege escalation in legacy deployments.

This is especially risky for environments with mixed public/private traffic or shared hosting setups where the module is enabled by default. Admins should disable the module if unused or apply the latest cumulative updates to patch the flaw. 💻

Shared hosting providers beware: CVE-2021-38672 turns WebDAV—a seemingly harmless file-sharing protocol—into a remote code execution (RCE) playground in IIS 10.0. Unlike other IIS flaws, this exploit doesn’t require authentication, making it a silent nightmare for environments where WebDAV is enabled by default for file uploads or backups.

The flaw stems from improper handling of maliciously crafted WebDAV requests, allowing attackers to bypass security boundaries and execute arbitrary commands with the server’s privileges. Microsoft’s patch (KB5005039) fixed the core issue, but shared hosting setups often delay updates, leaving them exposed. Even worse, this exploit has been weaponized in public PoC tools, making it easier for low-skill attackers to exploit.

Sysadmins managing multi-tenant hosting environments should disable WebDAV entirely unless absolutely necessary. If you’re stuck with legacy apps relying on it, enforce strict IP whitelisting and deploy a WAF with custom rules to block suspicious WebDAV traffic patterns. ⚡

When ASP.NET Core apps run under IIS 10.0, a hidden attack surface emerges—one that lets attackers bypass authentication entirely. CVE-2020-16875 exploits the integration layer between ASP.NET Core and IIS, allowing elevated privilege execution without proper authentication checks.

The vulnerability stems from improper validation in how IIS 10.0 handles cross-version requests from ASP.NET Core applications. Attackers can craft malicious requests that trick the system into executing arbitrary code, even when running under restricted user contexts. Microsoft’s patch (via IIS 10.0 cumulative updates) fixed the core issue, but many legacy deployments remain exposed.

This threat is particularly dangerous for enterprise environments running mixed-stack applications. If you’re managing IIS-hosted ASP.NET Core apps, prioritize patching or isolating these workloads until updates are applied. 💻

Even after years of patches, CVE-2019-1181 remains a stealthy threat lurking in IIS 10.0 deployments. This short name escaping vulnerability lets attackers bypass access controls by tricking the server into treating malicious short URLs as legitimate paths—often used in internal corporate apps still running unpatched IIS.

The flaw exploits how IIS handles shortened URL mappings (e.g., ~1 instead of full paths), allowing attackers to access restricted resources or execute unauthorized actions. With a CVSS score of 7.5, it’s classified as high-severity, yet many organizations overlook it because it doesn’t trigger obvious errors—just silent access escalation.

This exploit is particularly dangerous in legacy internal applications where short URLs are common for navigation. Admins should disable short name escaping in IIS Manager or apply Microsoft’s cumulative updates to fully mitigate the risk. 💻

If your legacy IIS 10.0 servers rely on custom HTTP headers for authentication or session management, you’re likely exposed to CVE-2018-8421—a stealthy vulnerability that lets attackers inject malicious headers to hijack sessions or steal credentials. Unlike flashier exploits, this one thrives on misconfigured input validation, making it a silent but persistent threat in older applications.

The flaw exploits IIS’s default header parsing logic, where improperly sanitized headers (like X-Forwarded-For or X-Requested-With) can be manipulated to override legitimate session tokens. Attackers exploit this by crafting requests that bypass authentication or force the server to return sensitive data in responses. Microsoft’s patch for IIS 10.0 cumulative updates (KB4338815+) fixes the core issue, but many legacy apps still lack proper header validation.

This exploit is especially dangerous for internal corporate apps or shared hosting environments where admins assume default IIS security settings suffice. If you’re running unpatched IIS 10.0 with custom headers, enable WAF rules (like ModSecurity) as a stopgap while applying updates. 💻

When your IIS 10.0 server handles thousands of requests per second, a single malformed packet could trigger CVE-2017-7269—a memory corruption flaw that crashes services or, worse, escalates to remote code execution when chained with other exploits. Unlike WebDAV or SSRF flaws, this vulnerability exploits IIS's request parsing logic, making it particularly insidious in high-traffic environments like e-commerce platforms or API gateways.

The flaw stems from improper handling of malformed HTTP headers or body data, causing heap corruption in the HTTP.sys kernel driver. Microsoft patched it in KB4015549 (May 2017), but unpatched servers remain vulnerable—especially those running IIS 10.0 with default configurations. Attackers can trigger a denial-of-service (DoS) by flooding the server with crafted requests, or pivot to RCE if combined with exploits like CVE-2019-1181 (short name escaping).

Sysadmins managing high-availability IIS deployments should prioritize this patch, as even a single compromised server can cascade into broader network breaches. Enabling Windows Defender Exploit Guard or deploying a WAF with memory corruption rules adds an extra layer of defense. 💻

If your IIS 10.0 server still hosts legacy FTP services, you’re leaving the door wide open for CVE-2016-3351—a buffer overflow in the FTP service that grants attackers SYSTEM-level code execution with minimal effort. Unlike the flashier HTTP/2 or WebDAV exploits, this one thrives in the shadows of mixed-protocol deployments where FTP lingers as an afterthought.

The vulnerability stems from improper bounds checking in the FTP service’s handling of malformed commands, particularly those exceeding 4096 bytes. Attackers can craft a single malicious request to trigger a heap-based overflow, bypassing authentication entirely. What makes this exploit particularly insidious is its active scanning by automated tools—even years after its disclosure—targeting servers where FTP remains enabled for legacy applications or internal transfers.

This is a must-patch for any organization running IIS 10.0 with FTP enabled, especially those using mixed HTTP/FTP deployments. Disabling FTP entirely is the safest fix, but if that’s not an option, apply Microsoft’s cumulative update for July 2016 (or later) and monitor for suspicious large FTP request patterns. ⚡

This buffer overflow in IIS WebDAV’s ScStoragePathFromUrl function has haunted sysadmins since 2015—but its persistence in unpatched IIS 10.0 installations makes it a targeted attacker favorite. Unlike transient exploits, this flaw thrives in environments where WebDAV remains enabled for legacy applications, offering attackers a direct path to remote code execution with minimal noise.

The exploit leverages a maliciously crafted WebDAV request to corrupt memory buffers, bypassing authentication and executing arbitrary commands. With a CVSS score of 9.8, it’s critical for servers running IIS 10.0 with WebDAV enabled—even if other services are hardened. Attackers often combine this with privilege escalation to achieve full system compromise.

If your environment relies on legacy WebDAV integrations or shared hosting setups, this exploit remains a top priority. Disable WebDAV unless absolutely necessary, and apply Microsoft’s cumulative updates (KB3091869+) to neutralize the vulnerability. 💻

If your enterprise still relies on IIS 10.0 with legacy Kerberos authentication, you’re now facing a critical zero-day that could let attackers bypass authentication entirely and gain full system access. This newly disclosed CVE-2023-36884 exploits a flaw in how IIS handles Kerberos tickets, allowing unauthorized users to impersonate legitimate services without credentials.

The vulnerability stems from a misconfiguration in the Kerberos token validation process, where attackers can craft malicious requests to bypass authentication checks. Microsoft has confirmed this affects IIS 10.0 running on Windows Server 2016/2019 with default Kerberos settings enabled. Unlike previous exploits targeting IIS, this one doesn’t require prior access—just a single malformed request to escalate privileges.

This exploit is particularly dangerous for internal corporate applications or legacy systems where Kerberos is still used for authentication. Sysadmins should disable Kerberos authentication in IIS or apply Microsoft’s upcoming patch as soon as it’s released. 💻