CVE Description

The Microsoft Exchange Server (affected versions) contains a Reflected Cross-Site Scripting (R-XSS) vulnerability that allows remote attackers to inject arbitrary web scripts or HTML. This vulnerability arises due to improper input validation in the /autodiscover/autodiscover.json endpoint.

By exploiting this vulnerability, an attacker can execute malicious scripts within the victim’s browser and potentially hijack sessions or steal sensitive information.

XSS Description

Cross-site scripting (XSS) is a web security vulnerability that allows an attacker to compromise the interactions that users have with a vulnerable application. It enables an attacker to circumvent the same-origin policy, which is designed to segregate different websites from each other.

XSS vulnerabilities allow an attacker to:

  • Masquerade as a victim user
  • Carry out actions that the user can perform
  • Access the user's data
  • If the victim has privileged access, the attacker can take full control over the application's functionality and data

Steps to Identify

  1. Perform spidering or crawling to gather application URLs.
  2. Check if the application has the following path: /autodiscover/autodiscover.json.
  3. Change the HTTP request method from GET to POST.
  4. Inject an XSS payload into the request body:

    POST /autodiscover/autodiscover.json HTTP/1.1
    Host: target.com
    Content-Type: application/x-www-form-urlencoded
    
    %3Cscript%3Ealert%28document.domain%29%3B+a=%22%3C%2Fscript%3E&x=1
  1. Observe if an alert pop-up appears—if yes, the application is vulnerable to XSS.

Impact

Successful exploitation of this vulnerability can lead to severe security risks, including:

  • Session Hijacking: An attacker can steal session cookies, gaining unauthorized access to a victim's account.
  • Data Theft: Sensitive user data, including login credentials and personal details, can be extracted.
  • Defacement: The attacker may modify web content, leading to misinformation or reputational damage.
  • Privilege Escalation: If an administrator account is compromised, an attacker could gain full control over the application.

Remediation

To mitigate this vulnerability, apply the following security best practices:

  • Apply Microsoft Security Patches: Ensure that all Microsoft Exchange Server instances are updated with the latest security patches.
  • Implement Proper Input Validation: Use server-side validation to sanitize user inputs and prevent script injection.
  • Use Content Security Policy (CSP): Restrict the execution of unauthorized scripts in the browser.
  • Enable HTTPOnly and Secure Cookies: Prevent session hijacking by ensuring cookies are protected from JavaScript access.

PoC Video

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