security-scan

name

security-scan

description

Deep security scanning for .NET applications across 6 layers: vulnerable packages, secrets detection, OWASP code patterns, auth configuration, CORS policy, and data protection. Produces severity-rated findings with specific remediation steps. Load this skill when: "security scan", "security audit", "check for vulnerabilities", "find secrets", "OWASP", "auth review", "CORS check", "security review", "penetration test prep", "CVE check", "vulnerability scan", "hardcoded password", "data protection", "security posture".

Security Scan

Core Principles

1. Defense in depth — Scan multiple layers: packages, source code, configuration, and infrastructure. A project with zero CVEs can still have hardcoded secrets, SQL injection, and missing auth. Each layer catches different vulnerability classes.

2. Prioritize by exploitability — A Critical SQL injection in a public endpoint is more urgent than a Low-severity info disclosure in an admin-only page. Prioritize findings by: exploitability (how easy to exploit), impact (what an attacker gains), and exposure (public vs internal endpoint).

3. No false sense of security — This is static analysis, not a penetration test. It catches known patterns but misses business logic flaws, authorization bypass through complex flows, and runtime-only vulnerabilities. State this clearly in every report.

4. Actionable findings — Every issue includes severity, file and line, description of the vulnerability, impact if exploited, and specific remediation code. "Fix the security issue" is not a finding. "OrderController.cs:23 — Missing [Authorize] on DELETE /orders/{id}. Impact: unauthenticated users can delete orders. Fix: Add [Authorize(Policy = \"OrderAdmin\")]" is.

5. Follow OWASP Top 10 — Structure the scan around known vulnerability categories. The OWASP Top 10 is the industry baseline for web application security. Every finding should map to an OWASP category.

Patterns

6-Layer Security Scan Pipeline

Execute all 6 layers. Each produces findings rated Critical, High, Medium, or Low.

Layer 1: Package Vulnerabilities

dotnet list package --vulnerable --include-transitive

Check for known CVEs in direct and transitive dependencies.

Severity mapping:

• Critical: CVSS 9.0-10.0 — Remote code execution, authentication bypass
• High: CVSS 7.0-8.9 — Privilege escalation, data exposure
• Medium: CVSS 4.0-6.9 — Denial of service, information disclosure
• Low: CVSS 0.1-3.9 — Minor information leakage

Remediation pattern:

<!-- BEFORE — vulnerable package -->
<PackageReference Include="System.Text.Json" Version="8.0.0" />

<!-- AFTER — patched version -->
<PackageReference Include="System.Text.Json" Version="10.0.0" />

If a patch isn't available, document the risk and apply compensating controls.

Layer 2: Secrets Detection

Scan all .cs, .json, .yml, .yaml, .xml, and .config files for hardcoded secrets.

Patterns to detect:

HIGH-CONFIDENCE PATTERNS (almost always a real secret):
- "Password=" or "Pwd=" in connection strings outside appsettings.Development.json
- "Bearer " followed by a base64 token in source code
- "-----BEGIN PRIVATE KEY-----" or "-----BEGIN RSA PRIVATE KEY-----"
- AWS: "AKIA" followed by 16 alphanumeric characters
- Azure: strings matching Azure Storage/Service Bus key patterns

MEDIUM-CONFIDENCE PATTERNS (need context to determine):
- "ApiKey", "Secret", "Token" as variable names with string literal assignments
- Base64-encoded strings longer than 40 characters in source code
- Connection strings with server addresses in non-Development config files

FALSE-POSITIVE INDICATORS (skip these):
- Values in appsettings.Development.json (development-only)
- Placeholder values: "your-key-here", "changeme", "TODO", empty strings
- Test fixtures with obviously fake values
- User secrets references: "UserSecretsId" in .csproj

Remediation:

// BAD — hardcoded connection string
var connectionString = "Server=prod-db;Database=Orders;User=admin;Password=S3cret!";

// GOOD — configuration with user secrets / environment variables
var connectionString = builder.Configuration.GetConnectionString("OrdersDb");
// Store actual values in:
// - Development: dotnet user-secrets set "ConnectionStrings:OrdersDb" "..."
// - Production: Environment variable or Azure Key Vault

Layer 3: OWASP Code Patterns

Scan source code for vulnerability patterns mapped to OWASP Top 10.

A03:2021 — Injection
  Detect: String concatenation in SQL queries, raw SQL with user input
  Pattern: FromSqlRaw($"SELECT * FROM Orders WHERE Id = '{userInput}'")
  Fix: FromSqlInterpolated($"SELECT * FROM Orders WHERE Id = {userInput}")
       or use parameterized queries / LINQ

A07:2021 — Cross-Site Scripting (XSS)
  Detect: Raw HTML output without encoding in Razor/Blazor
  Pattern: @Html.Raw(userInput)
  Fix: Use Razor's default encoding (@userInput) or sanitize explicitly

A08:2021 — Insecure Deserialization
  Detect: BinaryFormatter, JsonConvert with TypeNameHandling.All
  Pattern: JsonConvert.DeserializeObject<T>(json, new JsonSerializerSettings
           { TypeNameHandling = TypeNameHandling.All })
  Fix: Use System.Text.Json (no type name handling by default)
       If Newtonsoft is required: TypeNameHandling.None + explicit type converters

A02:2021 — Cryptographic Failures
  Detect: MD5, SHA1 for security purposes, ECB mode, hardcoded encryption keys
  Pattern: MD5.Create().ComputeHash(...)
  Fix: Use SHA256 minimum, prefer HMACSHA256 for authentication
       Use AES-GCM for encryption, derive keys from passwords using Rfc2898DeriveBytes

A04:2021 — Insecure Direct Object References
  Detect: Endpoints that use user-supplied IDs without ownership verification
  Pattern: GET /orders/{id} — returns any order regardless of who owns it
  Fix: Add ownership check: where o.Id == id && o.CustomerId == currentUser.Id

Layer 4: Auth Configuration

Review authentication and authorization setup across the application.

CHECKLIST:
1. All endpoints have explicit auth attributes
   - MCP: find_references(symbolName: "AllowAnonymous") — list deliberately public endpoints
   - MCP: find_references(symbolName: "Authorize") — list protected endpoints
   - Gap: endpoints with neither attribute (implicit policy depends on global config)

2. JWT validation settings are secure
   - ValidateIssuer: true (prevents token from wrong issuer)
   - ValidateAudience: true (prevents token meant for another app)
   - ValidateLifetime: true (prevents expired tokens)
   - ValidateIssuerSigningKey: true (prevents tampered tokens)
   - ClockSkew: TimeSpan.FromMinutes(1) max (default 5 min is too generous)

3. Authorization policies are specific
   - BAD: [Authorize] with no policy — just checks "is authenticated"
   - GOOD: [Authorize(Policy = "OrderAdmin")] — role/claim-based authorization

4. No auth bypass patterns
   - Middleware ordering: UseAuthentication() before UseAuthorization()
   - No global AllowAnonymous that accidentally opens everything
   - API key validation in middleware, not in each controller

// BAD — JWT configuration with weak validation
builder.Services.AddAuthentication().AddJwtBearer(options =>
{
    options.TokenValidationParameters = new()
    {
        ValidateIssuer = false,          // Anyone can issue tokens
        ValidateAudience = false,        // Token works for any app
        ValidateLifetime = false,        // Expired tokens accepted
        IssuerSigningKey = new SymmetricSecurityKey(
            "short-key"u8.ToArray())     // Key too short (< 256 bits)
    };
});

// GOOD — secure JWT configuration
builder.Services.AddAuthentication().AddJwtBearer(options =>
{
    options.TokenValidationParameters = new()
    {
        ValidateIssuer = true,
        ValidIssuer = builder.Configuration["Jwt:Issuer"],
        ValidateAudience = true,
        ValidAudience = builder.Configuration["Jwt:Audience"],
        ValidateLifetime = true,
        ClockSkew = TimeSpan.FromMinutes(1),
        ValidateIssuerSigningKey = true,
        IssuerSigningKey = new SymmetricSecurityKey(
            Convert.FromBase64String(builder.Configuration["Jwt:Key"]!))
    };
});

Layer 5: CORS Configuration

Review Cross-Origin Resource Sharing policy for misconfigurations.

// CRITICAL — wildcard origin with credentials
builder.Services.AddCors(options =>
{
    options.AddDefaultPolicy(policy =>
    {
        policy.AllowAnyOrigin()      // Any website can call this API
              .AllowCredentials();    // ...and send cookies/auth headers
        // This is a security vulnerability — browsers block this combo,
        // but it signals a misunderstanding of CORS
    });
});

// HIGH — wildcard origin without credentials
policy.AllowAnyOrigin()             // Any website can read API responses
      .AllowAnyHeader()
      .AllowAnyMethod();
// Acceptable ONLY for truly public APIs (e.g., public data feeds)

// GOOD — explicit origins
builder.Services.AddCors(options =>
{
    options.AddDefaultPolicy(policy =>
    {
        policy.WithOrigins(
                builder.Configuration.GetSection("Cors:AllowedOrigins").Get<string[]>()!)
              .AllowCredentials()
              .WithMethods("GET", "POST", "PUT", "DELETE")
              .WithHeaders("Content-Type", "Authorization");
    });
});

Check for:

• Wildcard origins (AllowAnyOrigin) — should be restricted to specific domains
• Exposed headers that leak internal information
• Overly broad methods (allowing PATCH, OPTIONS when only GET/POST needed)
• CORS in development vs production — different policies for different environments

Layer 6: Data Protection

Scan for PII and sensitive data handling issues.

CHECKS:
1. PII in logs — email, phone, SSN, credit card in logging statements
   Pattern: logger.LogInformation("User {Email} placed order", user.Email)
   Fix: logger.LogInformation("User {UserId} placed order", user.Id)
   Rule: Log identifiers (IDs), not identity data (email, name, phone)

2. Sensitive data in responses — returning more data than needed
   Pattern: Returning full User entity (with password hash) from an endpoint
   Fix: Use a response DTO that excludes sensitive fields

3. Missing Data Protection API — storing sensitive data without encryption
   Pattern: Storing API keys as plain text in the database
   Fix: Use IDataProtector to encrypt before storage

4. Unencrypted sensitive configuration — secrets in appsettings.json
   Pattern: "SmtpPassword": "actualpassword" in appsettings.json
   Fix: Use user secrets (dev), Key Vault (prod), or environment variables

// BAD — PII in logs
logger.LogInformation("Order placed by {Email} for {CreditCard}",
    order.CustomerEmail, order.PaymentCard);

// GOOD — identifiers only
logger.LogInformation("Order {OrderId} placed by customer {CustomerId}",
    order.Id, order.CustomerId);

Full Scan Report

Each finding uses format: #### [SEVERITY] File:Line — Title with OWASP Category, Description, Impact, and Remediation (with code before/after).

## Security Scan Report

**Project:** MyApp | **Date:** 2026-03-04 | **Scanner:** Claude (static analysis)

> This is a static analysis scan. It catches known patterns but does not replace
> penetration testing, dynamic analysis, or threat modeling.

### Summary

| Severity | Count |
|----------|-------|
| Critical | 0 |
| High | 2 |
| Medium | 3 |
| Low | 1 |

### Findings

#### [HIGH] src/Orders/Features/SearchOrders.cs:34 — SQL Injection
...

#### [HIGH] src/Api/Program.cs:12 — Missing Authorization on DELETE endpoint
...

### Layer Results

| Layer | Status | Findings |
|-------|--------|----------|
| 1. Package Vulnerabilities | PASS | 0 CVEs |
| 2. Secrets Detection | PASS | No hardcoded secrets |
| 3. OWASP Code Patterns | FAIL | 1 SQL injection, 1 insecure deserialization |
| 4. Auth Configuration | WARN | 2 endpoints missing explicit auth |
| 5. CORS Configuration | PASS | Origins properly restricted |
| 6. Data Protection | WARN | PII found in 2 log statements |

Anti-patterns

Only Scanning Packages

# BAD — NuGet packages are clean, declare victory
dotnet list package --vulnerable → "No vulnerable packages found"
"Security scan passed!"
# Missed: hardcoded password in appsettings.json, SQL injection in SearchOrders,
# missing [Authorize] on 3 endpoints, PII in logs

# GOOD — all 6 layers for complete coverage
Layer 1 (Packages): PASS
Layer 2 (Secrets): Found connection string in appsettings.Production.json
Layer 3 (OWASP): SQL injection in SearchOrders.cs:34
Layer 4 (Auth): 3 endpoints without [Authorize]
Layer 5 (CORS): Wildcard origin in production config
Layer 6 (Data): Customer email logged at Information level

Everything is Critical

# BAD — alert fatigue from over-classification
[CRITICAL] Missing XML comment on public method
[CRITICAL] Using var instead of explicit type
[CRITICAL] Connection string in appsettings.Development.json

# GOOD — severity matches actual risk
[LOW] Missing XML comment on public method (not a security issue)
[INFO] appsettings.Development.json has connection string (expected for dev)
[HIGH] appsettings.Production.json has hardcoded password (real secret exposure)

Scanning Without Context

# BAD — flagging test fixtures as security issues
[HIGH] Tests/OrderTests.cs:15 — Hardcoded API key: "test-key-12345"
# This is a test fixture with a fake value, not a real secret

# GOOD — context-aware scanning
Skip files in test projects for secret detection (test data is expected to be fake).
Flag only if the pattern matches a real secret format (e.g., starts with "AKIA" for AWS).

No Remediation Steps

# BAD — finding without a fix
[HIGH] SQL Injection in SearchOrders.cs:34
"Fix this."

# GOOD — finding with specific remediation
[HIGH] SQL Injection in SearchOrders.cs:34
Current: FromSqlRaw($"SELECT * FROM Orders WHERE Name LIKE '%{search}%'")
Fix: Use parameterized query:
  db.Orders.Where(o => EF.Functions.Like(o.Name, $"%{search}%"))
Impact: Attacker can read/modify/delete any data in the database.

Decision Guide

Scenario	Layers	Notes
Pre-release security gate	All 6	Full scan, non-negotiable before production
After dependency update	1	Package vulnerabilities only
New endpoint added	3, 4, 5	OWASP, auth, CORS for the new endpoint
Auth system changes	4	Deep auth configuration review
Config file changes	2	Secrets detection in changed configs
Logging changes	6	Check for PII in new log statements
Pre-pentest preparation	All 6	Fix static issues before paying for a pentest
Incident response	All 6	Full scan after a security incident
Quarterly security review	All 6	Regular cadence, also useful for onboarding
Public API exposure	3, 4, 5	Focus on external attack surface
Internal service	1, 2, 3	Lower CORS/auth scrutiny if truly internal