top-web-vulnerabilities skill
This skill should be used when the user asks to "identify web application vulnerabilities", "explain common security flaws", "understand vulnerability categories", "learn about injection attacks", "review access control weaknesses", "analyze API security issues", "assess security misconfigurations", "understand client-side vulnerabilities", "examine mobile and IoT security flaws", or "reference the OWASP-aligned vulnerability taxonomy". Use this skill to provide comprehensive vulnerability definitions, root causes, impacts, and mitigation strategies across all major web security categories.
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A skill is a folder. Copy it into your agent's skills folder and the agent loads it when the task matches its description.
git clone --depth 1 https://github.com/zebbern/claude-code-guide.git /tmp/claude-code-guide mkdir -p ~/.claude/skills cp -r /tmp/claude-code-guide/skills/top-web-vulnerabilities ~/.claude/skills/top-web-vulnerabilities
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In the Claude apps, zip the folder and upload it from the Skills settings. The folder on GitHub
The instructions your agent would load
SKILL.md as published, without the frontmatter. Read it on GitHub
Top 100 Web Vulnerabilities Reference
Purpose
Provide a comprehensive, structured reference for the 100 most critical web application vulnerabilities organized by category. This skill enables systematic vulnerability identification, impact assessment, and remediation guidance across the full spectrum of web security threats. Content organized into 15 major vulnerability categories aligned with industry standards and real-world attack patterns.
Prerequisites
- Basic understanding of web application architecture (client-server model, HTTP protocol)
- Familiarity with common web technologies (HTML, JavaScript, SQL, XML, APIs)
- Understanding of authentication and authorization concepts
- Access to web application security testing tools (Burp Suite, OWASP ZAP)
- Knowledge of secure coding principles recommended
Outputs and Deliverables
- Complete vulnerability catalog with definitions, root causes, impacts, and mitigations
- Category-based vulnerability groupings for systematic assessment
- Quick reference for security testing and remediation
- Foundation for vulnerability assessment checklists and security policies
Core Workflow
Phase 1: Injection Vulnerabilities Assessment
Evaluate injection attack vectors targeting data processing components:
SQL Injection (1)
- Definition: Malicious SQL code inserted into input fields to manipulate database queries
- Root Cause: Lack of input validation, improper use of parameterized queries
- Impact: Unauthorized data access, data manipulation, database compromise
- Mitigation: Use parameterized queries/prepared statements, input validation, least privilege database accounts
Cross-Site Scripting - XSS (2)
- Definition: Injection of malicious scripts into web pages viewed by other users
- Root Cause: Insufficient output encoding, lack of input sanitization
- Impact: Session hijacking, credential theft, website defacement
- Mitigation: Output encoding, Content Security Policy (CSP), input sanitization
Command Injection (5, 11)
- Definition: Execution of arbitrary system commands through vulnerable applications
- Root Cause: Unsanitized user input passed to system shells
- Impact: Full system compromise, data exfiltration, lateral movement
- Mitigation: Avoid shell execution, whitelist valid commands, strict input validation
XML Injection (6), LDAP Injection (7), XPath Injection (8)
- Definition: Manipulation of XML/LDAP/XPath queries through malicious input
- Root Cause: Improper input handling in query construction
- Impact: Data exposure, authentication bypass, information disclosure
- Mitigation: Input validation, parameterized queries, escape special characters
Server-Side Template Injection - SSTI (13)
- Definition: Injection of malicious code into template engines
- Root Cause: User input embedded directly in template expressions
- Impact: Remote code execution, server compromise
- Mitigation: Sandbox template engines, avoid user input in templates, strict input validation
Phase 2: Authentication and Session Security
Assess authentication mechanism weaknesses:
Session Fixation (14)
- Definition: Attacker sets victim's session ID before authentication
- Root Cause: Session ID not regenerated after login
- Impact: Session hijacking, unauthorized account access
- Mitigation: Regenerate session ID on authentication, use secure session management
Brute Force Attack (15)
- Definition: Systematic password guessing using automated tools
- Root Cause: Lack of account lockout, rate limiting, or CAPTCHA
- Impact: Unauthorized access, credential compromise
- Mitigation: Account lockout policies, rate limiting, MFA, CAPTCHA
Session Hijacking (16)
- Definition: Attacker steals or predicts valid session tokens
- Root Cause: Weak session token generation, insecure transmission
- Impact: Account takeover, unauthorized access
- Mitigation: Secure random token generation, HTTPS, HttpOnly/Secure cookie flags
Credential Stuffing and Reuse (22)
- Definition: Using leaked credentials to access accounts across services
- Root Cause: Users reusing passwords, no breach detection
- Impact: Mass account compromise, data breaches
- Mitigation: MFA, breach password checks, unique credential requirements
Insecure "Remember Me" Functionality (85)
- Definition: Weak persistent authentication token implementation
- Root Cause: Predictable tokens, inadequate expiration controls
- Impact: Unauthorized persistent access, session compromise
- Mitigation: Strong token generation, proper expiration, secure storage
CAPTCHA Bypass (86)
- Definition: Circumventing bot detection mechanisms
- Root Cause: Weak CAPTCHA algorithms, improper validation
- Impact: Automated attacks, credential stuffing, spam
- Mitigation: reCAPTCHA v3, layered bot detection, rate limiting
Phase 3: Sensitive Data Exposure
Identify data protection failures:
IDOR - Insecure Direct Object References (23, 42)
- Definition: Direct access to internal objects via user-supplied references
- Root Cause: Missing authorization checks on object access
- Impact: Unauthorized data access, privacy breaches
- Mitigation: Access control validation, indirect reference maps, authorization checks
Data Leakage (24)
- Definition: Inadvertent disclosure of sensitive information
- Root Cause: Inadequate data protection, weak access controls
- Impact: Privacy breaches, regulatory penalties, reputation damage
- Mitigation: DLP solutions, encryption, access controls, security training
Unencrypted Data Storage (25)
- Definition: Storing sensitive data without encryption
- Root Cause: Failure to implement encryption at rest
- Impact: Data breaches if storage compromised
- Mitigation: Full-disk encryption, database encryption, secure key management
Information Disclosure (33)
- Definition: Exposure of system details through error messages or responses
- Root Cause: Verbose error handling, debug information in production
- Impact: Reconnaissance for further attacks, credential exposure
- Mitigation: Generic error messages, disable debug mode, secure logging
Phase 4: Security Misconfiguration
Assess configuration weaknesses:
Missing Security Headers (26)
- Definition: Absence of protective HTTP headers (CSP, X-Frame-Options, HSTS)
- Root Cause: Inadequate server configuration
- Impact: XSS attacks, clickjacking, protocol downgrade
- Mitigation: Implement CSP, X-Content-Type-Options, X-Frame-Options, HSTS
Default Passwords (28)
- Definition: Unchanged default credentials on systems/applications
- Root Cause: Failure to change vendor defaults
- Impact: Unauthorized access, system compromise
- Mitigation: Mandatory password changes, strong password policies
Directory Listing (29)
- Definition: Web server exposes directory contents
- Root Cause: Improper server configuration
- Impact: Information disclosure, sensitive file exposure
- Mitigation: Disable directory indexing, use default index files
Unprotected API Endpoints (30)
- Definition: APIs lacking authentication or authorization
- Root Cause: Missing security controls on API routes
- Impact: Unauthorized data access, API abuse
- Mitigation: OAuth/API keys, access controls, rate limiting
Open Ports and Services (31)
- Definition: Unnecessary network services exposed
- Root Cause: Failure to minimize attack surface
- Impact: Exploitation of vulnerable services
- Mitigation: Port scanning audits, firewall rules, service minimization
Misconfigured CORS (35)
- Definition: Overly permissive Cross-Origin Resource Sharing policies
- Root Cause: Wildcard origins, improper CORS configuration
- Impact: Cross-site request attacks, data theft
- Mitigation: Whitelist trusted origins, validate CORS headers
Unpatched Software (34)
- Definition: Systems running outdated vulnerable software
- Root Cause: Neglected patch management
- Impact: Exploitation of known vulnerabilities
- Mitigation: Patch management program, vulnerability scanning, automated updates
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