See also Misconfigured IIS Request Filtering
TLDR: Misconfigured IIS (Internet Information Services), highlighted in the OWASP Top Ten under “Security Misconfiguration,” can lead to unauthorized access, data breaches, and performance degradation. Issues such as retaining default settings, improper authentication configurations, and weak SSL/TLS protocols compromise server security. Properly configuring IIS, introduced by Microsoft in 1995, ensures the secure delivery of web applications and services.
https://en.wikipedia.org/wiki/Internet_Information_Services
One of the most common issues in misconfigured IIS servers is retaining default settings. Default configurations may include open endpoints, weak authentication settings, and generic error messages that provide attackers with useful information. OWASP recommends hardening default settings by disabling unused features and customizing server configurations.
https://learn.microsoft.com/en-us/iis/
Improper directory permissions are another frequent vulnerability. Granting excessive permissions to web directories, such as `Full Control` for `Everyone`, exposes files to unauthorized modification or deletion. OWASP advises implementing the principle of least privilege to ensure that only authorized accounts have access to critical directories.
https://owasp.org/www-project-cheat-sheets/cheatsheets/Access_Control_Cheat_Sheet.html
Allowing directory browsing in IIS servers creates another layer of risk. Exposing directory contents allows attackers to enumerate files, potentially accessing sensitive data like backups or configuration files. OWASP recommends disabling directory browsing through the IIS Manager or configuration files.
https://owasp.org/www-project-top-ten/
Weak SSL/TLS configurations, such as allowing deprecated protocols like SSL 3.0 or TLS 1.0, leave servers vulnerable to attacks like man-in-the-middle attacks and data interception. OWASP advises enforcing strong TLS settings and disabling insecure protocols to protect transmitted data.
https://learn.microsoft.com/en-us/windows-server/security/tls/tls-guidance
Improper error handling configurations can reveal sensitive information about the server, such as stack traces or software versions, through detailed error messages. OWASP suggests using generic error pages for end users while securely logging detailed error information for internal debugging.
https://owasp.org/www-project-cheat-sheets/cheatsheets/Error_Handling_Cheat_Sheet.html
Exposing administrative interfaces without proper security measures increases the risk of unauthorized access. Attackers targeting these interfaces can modify configurations or disrupt services. OWASP advises securing admin panels with IP restrictions, strong passwords, and multi-factor authentication (MFA).
https://owasp.org/www-project-cheat-sheets/cheatsheets/Authentication_Cheat_Sheet.html
Neglecting to enable request filtering features in IIS can leave applications vulnerable to injection attacks and malicious payloads. OWASP recommends enabling IIS Request Filtering and defining strict rules to block harmful inputs and invalid requests.
https://learn.microsoft.com/en-us/iis/configuration/system.webserver/security/requestfiltering/
Another issue is failing to configure proper logging and monitoring. Without logging access attempts and server activity, it becomes challenging to detect and mitigate attacks. OWASP advises integrating IIS logs with SIEM tools to analyze and respond to potential threats.
https://owasp.org/www-project-cheat-sheets/cheatsheets/Logging_Cheat_Sheet.html
Neglecting to update and patch IIS regularly is a critical oversight. Outdated servers are vulnerable to known exploits and attacks. OWASP emphasizes maintaining a patch management schedule and subscribing to security updates from Microsoft to stay protected.
https://learn.microsoft.com/en-us/windows-server/security/
To mitigate these risks, administrators should perform regular audits, enforce secure configurations, and monitor server activity using tools like OWASP ZAP or Nessus. Adherence to OWASP Top Ten guidelines ensures that IIS servers remain robust and secure.