Detailed Technical Analysis of "50 Ways to Inject Your Neighbor"

Overview: Sebastian Lekies' presentation titled "50 Ways to Inject Your Neighbor" delivered at AppSec EU 2017 delves into numerous web injection vulnerabilities. The presentation focuses on attacks such as Cross-Site Scripting (XSS), Cross-Site Request Forgery (CSRF), and related injection flaws, providing detailed explanations and live demonstrations.

Key Technical Details:

1. Injection Vulnerabilities:

Injection vulnerabilities occur when untrusted data is sent to an interpreter as part of a command or query. The attacker’s hostile data tricks the interpreter into executing unintended commands or accessing unauthorized data.

Typical Types of Injection: - SQL Injection (SQLi): Involving maliciously crafted SQL queries. - Command Injection: Shell commands executed within web applications. - LDAP Injection: Crafting queries to LDAP directories. - Template Injection: Exploiting dynamic template rendering engines.

2. Cross-Site Scripting (XSS):

XSS is one of the most prevalent injection attacks. It allows attackers to inject malicious scripts into content from otherwise trusted websites.

Types of XSS: - Stored XSS: The payload is stored permanently on the target server, such as in a database, message forum, or visitor log.

Example: An attacker injects a script in a forum post, which is then rendered every time the post is viewed.

• Reflected XSS: The payload is reflected off the web server, such as in an error message or search result, and is delivered to other users via links.

Example: Manipulating search query parameters sent to users.

• DOM-based XSS: The payload is executed as a result of modifications in the web page DOM.

Example: Using JavaScript functions like document.write() or eval() which processes input improperly.

3. Client-Side Template Injection:

Client-Side Template Injection (CSTI) involves the manipulation of templates to include malicious payloads.

Template Engines: - Mustache: Used in environments where user-generated content is rendered. - Malicious User Input: Modifying templates like {{payload}} to inject arbitrary script execution.

4. Cross-Site Request Forgery (CSRF):

CSRF exploits the web application's trust in the user's browser. It tricks the victim into submitting a malicious request, typically via a crafted URL or form submission.

CSRF Defenses: - CSRF Tokens: Unique tokens per session or request to validate the legitimacy. - SameSite Attribute: Controls whether a cookie is sent with cross-site requests, which mitigates CSRF.

5. Advanced Injection Techniques:

Lekies discusses various bypass techniques that attackers can use to circumvent traditional security mechanisms.

• Polyglot Payloads: Payloads that can function across different contexts or interpreters.
• Encoding and Obfuscation: Altered encoding (Base64, URL encoding) to bypass input filters.
• Unicode and Alternate Encodings: Using different character encodings to evade signature-based detection mechanisms.

In-Depth Examples:

Polyglot XSS:

A typical scenario involves an input that serves multiple purposes (HTML/Text). By carefully crafting the input, an attacker can inject a payload that gets executed in a particular context.

Example:

<script>alert(1)</script>

This payload can be crafted to work across various interpreters, ensuring execution if any one of the filtering mechanisms fails.

Defense Mechanisms:

1. Input Validation and Output Encoding:
2. Validate and sanitize inputs. Use whitelisting over blacklisting.

3. Context-specific output encoding (e.g., HTML, URL, CSS) to neutralize potentially dangerous characters.

4. Content Security Policy (CSP):

5. Deploying a CSP restricts sources from where scripts can be loaded and executed.

6. Reduces the impact of XSS by blocking inline scripts and disallowing dynamic script execution (<script> tags), eval() calls.

7. Auto-Escaping:

8. Use frameworks that auto-escape variables within the templates.

9. Same-Origin Policy (SOP):

10. Ensuring cross-origin resources are accessed securely, leveraging web platform security features.

Key Takeaways:

• Versatility of Injection Attacks: Injection attacks extend beyond simple SQL and scripting inclusions. They encompass any untrusted input influencing the execution context.
• Comprehensive Filtering: Ensuring a layered security model that includes consistent input validation, context-aware output encoding, proper use of CSP, and continuously updated defense mechanisms.
• Understanding Attack Surfaces: A clear grasp of all the parsers (HTML, SQL, etc.) and the data they process within the application architecture helps identify and mitigate potential injection points.

Conclusion:

Sebastian Lekies' presentation highlights the depth and breadth of injection vulnerabilities affecting modern web applications. The live demonstrations and examples illustrate the potential impact and the necessity for robust defensive coding practices, comprehensive input validation, and systematized security protocols to protect web applications from such attacks.

For full details, check the original slides here.