Gruyere Learn Web Application Exploits Defenses Top
<html> <body> <form action="https://google-gruyere.appspot.com/[your-instance-id]/profile" method="POST"> <input type="hidden" name="name" value="AttackerName"> <input type="hidden" name="about" value="Hacked by CSRF"> </form> <script>document.forms[0].submit();</script> </body> </html>
Cross-Site Request Forgery tricks a victim into submitting a malicious request that inherits the victim's identity and privileges. For most sites, browser requests automatically include any credentials associated with the site, such as session cookies. Consequently, an authenticated site has no way to distinguish between a forged request and a legitimate one.
Path traversal (also called directory traversal) occurs when a program constructs a file path name using input from the user, resulting in access to an unintended file. Attackers inject sequences like ../ (dot-dot-slash) into file path parameters to navigate outside the application's root directory.
Manipulating input fields to alter backend database queries. gruyere learn web application exploits defenses top
An attacker might notice their profile URL is .../profile?user=alice and try changing it to .../profile?user=admin . If the server doesn't verify that the current user is actually "admin," the attacker gains unauthorized access. The Defense:
Stealing, modifying, or deleting database content. 4. Path Traversal
Inputting ' OR '1'='1 into a login field to force the backend logic to evaluate to true, logging the attacker in as the first user in the database. The Defense Path traversal (also called directory traversal) occurs when
It covers the most common and dangerous vulnerabilities [1].
Unlike reading a textbook, Gruyere forces you to find the bugs yourself [1].
Review the source code provided in the Gruyere lab interface. Identify how the application handles requests, parameters, and user sessions. An attacker might notice their profile URL is
Gruyere suffers from multiple forms of XSS, including Reflected XSS (injecting malicious payloads into URLs or input fields that are immediately mirrored back) and Stored XSS (saving a malicious script into a profile or a post snippet so that it executes whenever another user views that content). Attackers use this to steal session tokens, access sensitive DOM data, or deface pages.
Malicious scripts are injected through URL parameters or error messages, executing immediately upon rendering the page. 2. Cross-Site Request Forgery (CSRF)
Verify file types using magic bytes rather than relying strictly on the user-provided file extension. Summary of Top Exploits and Defenses Vulnerability Type Gruyere Exploit Mechanism Primary Defensive Strategy Stored XSS Injecting scripts into profile snippets. Contextual HTML output encoding. CSRF Exploiting predictable URL actions. Anti-CSRF tokens tied to user sessions. Path Traversal Using ../ in file upload names. Strict path resolution and whitelisting. IDOR / BOLA Guessing sequential object IDs. Server-side access control validation. Info Disclosure Triggering Python server stack traces. Global exception handling and generic errors. Moving Forward
