CVE-2015-5593

Step 1: Payload Delivery: An attacker crafts a malicious payload, typically a JavaScript snippet, designed to execute within the victim's browser. This payload is wrapped in HTML tags to bypass the sanitization function's intended filtering. Step 2: Input Injection: The attacker injects the crafted payload into a vulnerable input field within the Zenphoto application. This could be a comment field, a user profile field, or any other area where user-supplied data is displayed. Step 3: Data Storage (if applicable): The injected payload is stored in the Zenphoto database or other storage mechanism. Step 4: Victim Interaction: A victim accesses a page within the Zenphoto application that displays the attacker's injected payload. This could be a blog post, a user profile, or any page that renders the attacker's input. Step 5: Payload Execution: The victim's browser interprets and executes the malicious JavaScript code injected by the attacker. This allows the attacker to perform actions on behalf of the victim, such as stealing cookies, redirecting the user to a malicious website, or defacing the website.

The vulnerability stems from the sanitize_string function's inadequate handling of HTML tags. Specifically, the function fails to properly filter or escape malicious HTML tags and attributes, allowing attackers to inject arbitrary JavaScript code. The root cause is a flawed regular expression or logic within the sanitization function that permits the bypass of intended security measures. The vulnerability allows for the injection of malicious JavaScript code through crafted input, which is then executed in the context of the victim's browser. This is a classic XSS vulnerability, where the attacker controls the content displayed to the user.