Understanding Persistent XSS in Inout Webmail

What this paper is

This paper details a Persistent Cross-Site Scripting (XSS) vulnerability found in Inout Webmail, a webmail solution. The vulnerability allows an attacker to inject malicious scripts into the application that will then be executed by other users when they interact with the affected parts of the application. This means the malicious script "persists" within the application, rather than just being executed in the attacker's browser.

Simple technical breakdown

The core issue is that Inout Webmail doesn't properly check or clean user-provided data before storing and displaying it. When a user inputs something into fields like "contacts" or "emailfilter," and this input contains malicious JavaScript code, the application saves it as is. Later, when another user views this data (e.g., looking at contacts or email filter settings), the browser interprets and runs the embedded JavaScript. This can lead to various attacks, such as stealing session cookies, redirecting users to malicious sites, or defacing the web page.

Complete code and payload walkthrough

The provided paper does not contain any executable code or shellcode. It describes the vulnerability and provides example attack parameters and URLs.

• Attack parameter: "><script>alert("xss")</script>

  • Practical Purpose: This is a standard XSS payload. The "> part is designed to break out of any existing HTML attributes or tags that might be wrapping user input. The <script>alert("xss")</script> part is the actual JavaScript code that, when executed by a victim's browser, will display a pop-up box with the text "xss". This is a common proof-of-concept to demonstrate that XSS is possible.

• Example URLs:

  • http://server/path/index.php?page=mail/mailbox
  • http://server/index.php?page=settings/emailfilter
  • Practical Purpose: These URLs indicate the specific pages within the Inout Webmail application where the vulnerability is likely exploitable. The page parameter suggests that the application dynamically loads different modules or views based on its value. Injecting the malicious payload into input fields associated with these pages could lead to persistent XSS.

Mapping:

• "> (in attack parameter) -> Escapes HTML context.
• <script>alert("xss")</script> (in attack parameter) -> Executes JavaScript to demonstrate XSS.
• page=mail/mailbox (in URL) -> Target page for potential XSS in contact management.
• page=settings/emailfilter (in URL) -> Target page for potential XSS in email filtering rules.

Practical details for offensive operations teams

• Required Access Level: Typically, an attacker would need a low-privileged user account within the Inout Webmail application to inject the persistent payload. This is because the vulnerability lies in how user-submitted data is handled and stored, not in exploiting a server-side vulnerability that grants elevated privileges.
• Lab Preconditions:
  • A running instance of Inout Webmail (version vulnerable to this specific flaw).
  • A user account with login credentials for the Inout Webmail application.
  • Knowledge of which input fields are associated with the contacts and emailfilter functionalities.
• Tooling Assumptions:
  • A web browser to interact with the application.
  • A proxy tool (like Burp Suite or OWASP ZAP) is highly recommended for intercepting and modifying requests, making it easier to craft and inject payloads.
  • A text editor for constructing payloads.
• Execution Pitfalls:
  • Input Sanitization: Modern versions of Inout Webmail (or any web application) might have implemented input sanitization that could filter out or encode the payload. Testing different encoding methods or payload variations might be necessary.
  • Contextual Escaping: The effectiveness of the "> part of the payload depends on the specific HTML context where the user input is rendered. If the input is already within a JavaScript string or a different HTML attribute, the payload might need adjustment.
  • User Interaction: For the XSS to execute, a victim user must visit the page where the malicious data is displayed. This might require social engineering or other methods to lure victims.
  • Payload Delivery: The attacker needs to find a way to get the victim to view the data containing the payload. This could be by sharing a link to a contact entry, or by having the victim view their email filter settings.
• Telemetry:
  • Web Server Logs: Look for requests to the vulnerable pages (index.php with page=mail/mailbox or page=settings/emailfilter) that contain suspicious input in parameters that are not explicitly mentioned in the paper but are likely related to contact details or filter rules.
  • Application Logs: If the application logs user input or errors, these might show the injected script.
  • Victim Browser Activity: If the XSS payload is designed to exfiltrate data (e.g., cookies), monitoring network traffic from the victim's machine for outbound connections to attacker-controlled servers would be key.

Where this was used and when

• Context: This vulnerability was relevant to organizations using the Inout Webmail application for their website's email services.
• When: Published in December 2010. Exploitation would have been possible on Inout Webmail versions vulnerable at that time.

Defensive lessons for modern teams

• Input Validation and Sanitization: Always validate and sanitize all user-supplied input on both the client-side (for user experience) and, critically, on the server-side before storing or processing it. Use established libraries for sanitization to avoid common pitfalls.
• Output Encoding: When displaying user-supplied data in HTML, always encode it appropriately for the context. For example, use HTML entity encoding for data displayed within HTML tags, and JavaScript encoding for data displayed within JavaScript.
• Content Security Policy (CSP): Implement a strong CSP to restrict the sources from which scripts can be loaded and executed, significantly mitigating the impact of XSS vulnerabilities.
• Web Application Firewalls (WAFs): While not a foolproof solution, WAFs can help detect and block common XSS attack patterns.
• Regular Security Audits and Patching: Keep web applications and their dependencies updated with the latest security patches. Conduct regular security assessments to identify and address vulnerabilities proactively.

ASCII visual (if applicable)

This vulnerability is primarily about data flow within the application and how user input is handled. An ASCII diagram can illustrate the basic concept of persistent XSS:

+-----------------+      +-------------------+      +-----------------+
| Attacker        | ---> | Inout Webmail App | ---> | Victim's Browser|
| (Injects Script)|      | (Stores Data)     |      | (Executes Script)|
+-----------------+      +-------------------+      +-----------------+
        ^                                                     |
        |                                                     |
        +-----------------------------------------------------+
                      (Victim views stored data)

Explanation:

1. The Attacker crafts a malicious input containing a script.
2. The Inout Webmail App receives this input and, due to improper sanitization, stores it directly in its database or files.
3. Later, when a Victim accesses the application and views the data that contains the attacker's script (e.g., contacts list, email filter settings), the application retrieves and displays this data.
4. The Victim's Browser renders the HTML and encounters the script embedded within the data. It then executes this script, leading to the XSS attack.

Source references

• Paper ID: 15781
• Paper Title: Inout Webmail Script - Persistent Cross-Site Scripting
• Author: Sid3^effects
• Published: 2010-12-20
• Paper URL: https://www.exploit-db.com/papers/15781

Original Exploit-DB Content (Verbatim)

#Name :inoutwebmail Persistent Xss Vulnerability
#Date : Dec,20 2010
#Vendor Url :http://www.inoutscripts.com/
#Author : Sid3^effects aKa HaRi <shell_c99[at]yahoo.com>
#Big hugs : Th3 RDX,Hanan_butt,
#special thanks to : r0073r (inj3ct0r.com),L0rd CruSad3r,SeeMe,MaYur,MA1201,KeDar,Sonic,gunslinger_,Sn!pEr.S!Te,n4pst3rr,tranquiller,Sug@R
#greetz to :!Op3x_ninjato team,www.topsecure.net ,trent Dillman,All ICW members and my friends :) luv y0 guyz
#######################################################################################################
Description:
Inout Webmail is a complete webmail solution for your website. Build your own personal secure mail service today

###############################################################################################################
Exploit:Persistent Xss Vulnerability

The vulnerability exists due to failure in the script to properly sanitize user-supplied input.Successful exploitation of this vulnerability could result in a compromise of the application,disclosure or modification of sensitive data.


>The Xss vulnerability exists in "contacts",emailfilter
>Also the attacker can send malicious xss scripts to the users who are using this application

Attack parameter: "><script>alert("xss")</script>

>http://server/path/index.php?page=mail/mailbox
>http://server/index.php?page=settings/emailfilter

###############################################################################################################
Fix:
   N/a
###############################################################################################################
# 0day no more
# Sid3^effects
# 1337day.com