OWASP Security Best Practices Skill

Apply these security standards when writing or reviewing code.

Quick Reference: OWASP Top 10:2025

Vulnerability Key Prevention

A01 Broken Access Control Deny by default, enforce server-side, verify ownership

A02 Security Misconfiguration Harden configs, disable defaults, minimize features

A03 Supply Chain Failures Lock versions, verify integrity, audit dependencies

A04 Cryptographic Failures TLS 1.2+, AES-256-GCM, Argon2/bcrypt for passwords

A05 Injection Parameterized queries, input validation, safe APIs

A06 Insecure Design Threat model, rate limit, design security controls

A07 Auth Failures MFA, check breached passwords, secure sessions

A08 Integrity Failures Sign packages, SRI for CDN, safe serialization

A09 Logging Failures Log security events, structured format, alerting

A10 Exception Handling Fail-closed, hide internals, log with context

Security Code Review Checklist

When reviewing code, check for these issues:

Input Handling

• All user input validated server-side

• Using parameterized queries (not string concatenation)

• Input length limits enforced

• Allowlist validation preferred over denylist

Authentication & Sessions

• Passwords hashed with Argon2/bcrypt (not MD5/SHA1)

• Session tokens have sufficient entropy (128+ bits)

• Sessions invalidated on logout

• MFA available for sensitive operations

Access Control

• Check for framework-level auth middleware (e.g., Next.js middleware.ts, proxy.ts, Express middleware) before flagging missing per-route auth

• Authorization checked on every request

• Using object references user cannot manipulate

• Deny by default policy

• Privilege escalation paths reviewed

Data Protection

• Sensitive data encrypted at rest

• TLS for all data in transit

• No sensitive data in URLs/logs

• Secrets in environment/vault (not code)

Error Handling

• No stack traces exposed to users

• Fail-closed on errors (deny, not allow)

• All exceptions logged with context

• Consistent error responses (no enumeration)

Secure Code Patterns

SQL Injection Prevention

UNSAFE

cursor.execute(f"SELECT * FROM users WHERE id = {user_id}")

SAFE

cursor.execute("SELECT * FROM users WHERE id = %s", (user_id,))

Command Injection Prevention

UNSAFE

os.system(f"convert {filename} output.png")

SAFE

subprocess.run(["convert", filename, "output.png"], shell=False)

Password Storage

UNSAFE

hashlib.md5(password.encode()).hexdigest()

SAFE

from argon2 import PasswordHasher PasswordHasher().hash(password)

Access Control

UNSAFE - No authorization check

@app.route('/api/user/<user_id>') def get_user(user_id): return db.get_user(user_id)

SAFE - Authorization enforced

@app.route('/api/user/<user_id>') @login_required def get_user(user_id): if current_user.id != user_id and not current_user.is_admin: abort(403) return db.get_user(user_id)

Error Handling

UNSAFE - Exposes internals

@app.errorhandler(Exception) def handle_error(e): return str(e), 500

SAFE - Fail-closed, log context

@app.errorhandler(Exception) def handle_error(e): error_id = uuid.uuid4() logger.exception(f"Error {error_id}: {e}") return {"error": "An error occurred", "id": str(error_id)}, 500

Fail-Closed Pattern

UNSAFE - Fail-open

def check_permission(user, resource): try: return auth_service.check(user, resource) except Exception: return True # DANGEROUS!

SAFE - Fail-closed

def check_permission(user, resource): try: return auth_service.check(user, resource) except Exception as e: logger.error(f"Auth check failed: {e}") return False # Deny on error

Agentic AI Security (OWASP 2026)

When building or reviewing AI agent systems, check for:

Risk Description Mitigation

ASI01: Goal Hijack Prompt injection alters agent objectives Input sanitization, goal boundaries, behavioral monitoring

ASI02: Tool Misuse Tools used in unintended ways Least privilege, fine-grained permissions, validate I/O

ASI03: Privilege Abuse Credential escalation across agents Short-lived scoped tokens, identity verification

ASI04: Supply Chain Compromised plugins/MCP servers Verify signatures, sandbox, allowlist plugins

ASI05: Code Execution Unsafe code generation/execution Sandbox execution, static analysis, human approval

ASI06: Memory Poisoning Corrupted RAG/context data Validate stored content, segment by trust level

ASI07: Agent Comms Spoofing between agents Authenticate, encrypt, verify message integrity

ASI08: Cascading Failures Errors propagate across systems Circuit breakers, graceful degradation, isolation

ASI09: Trust Exploitation Social engineering via AI Label AI content, user education, verification steps

ASI10: Rogue Agents Compromised agents acting maliciously Behavior monitoring, kill switches, anomaly detection

Agent Security Checklist

• All agent inputs sanitized and validated

• Tools operate with minimum required permissions

• Credentials are short-lived and scoped

• Third-party plugins verified and sandboxed

• Code execution happens in isolated environments

• Agent communications authenticated and encrypted

• Circuit breakers between agent components

• Human approval for sensitive operations

• Behavior monitoring for anomaly detection

• Kill switch available for agent systems

ASVS 5.0 Key Requirements

Level 1 (All Applications)

• Passwords minimum 12 characters

• Check against breached password lists

• Rate limiting on authentication

• Session tokens 128+ bits entropy

• HTTPS everywhere

Level 2 (Sensitive Data)

• All L1 requirements plus:

• MFA for sensitive operations

• Cryptographic key management

• Comprehensive security logging

• Input validation on all parameters

Level 3 (Critical Systems)

• All L1/L2 requirements plus:

• Hardware security modules for keys

• Threat modeling documentation

• Advanced monitoring and alerting

• Penetration testing validation

Language-Specific Security Quirks

Important: The examples below are illustrative starting points, not exhaustive. When reviewing code, think like a senior security researcher: consider the language's memory model, type system, standard library pitfalls, ecosystem-specific attack vectors, and historical CVE patterns. Each language has deeper quirks beyond what's listed here.

Different languages have unique security pitfalls. Here are the top 20 languages with key security considerations. Go deeper for the specific language you're working in:

JavaScript / TypeScript

Main Risks: Prototype pollution, XSS, eval injection

// UNSAFE: Prototype pollution Object.assign(target, userInput) // SAFE: Use null prototype or validate keys Object.assign(Object.create(null), validated)

// UNSAFE: eval injection eval(userCode) // SAFE: Never use eval with user input

Watch for: eval() , innerHTML , document.write() , prototype chain manipulation, proto

Python

Main Risks: Pickle deserialization, format string injection, shell injection

UNSAFE: Pickle RCE

pickle.loads(user_data)

SAFE: Use JSON or validate source

json.loads(user_data)

UNSAFE: Format string injection

query = "SELECT * FROM users WHERE name = '%s'" % user_input

SAFE: Parameterized

cursor.execute("SELECT * FROM users WHERE name = %s", (user_input,))

Watch for: pickle , eval() , exec() , os.system() , subprocess with shell=True

Java

Main Risks: Deserialization RCE, XXE, JNDI injection

// UNSAFE: Arbitrary deserialization ObjectInputStream ois = new ObjectInputStream(userStream); Object obj = ois.readObject();

// SAFE: Use allowlist or JSON ObjectMapper mapper = new ObjectMapper(); mapper.readValue(json, SafeClass.class);

Watch for: ObjectInputStream , Runtime.exec() , XML parsers without XXE protection, JNDI lookups

C#

Main Risks: Deserialization, SQL injection, path traversal

// UNSAFE: BinaryFormatter RCE BinaryFormatter bf = new BinaryFormatter(); object obj = bf.Deserialize(stream);

// SAFE: Use System.Text.Json var obj = JsonSerializer.Deserialize<SafeType>(json);

Watch for: BinaryFormatter , JavaScriptSerializer , TypeNameHandling.All , raw SQL strings

PHP

Main Risks: Type juggling, file inclusion, object injection

// UNSAFE: Type juggling in auth if ($password == $stored_hash) { ... } // SAFE: Use strict comparison if (hash_equals($stored_hash, $password)) { ... }

// UNSAFE: File inclusion include($_GET['page'] . '.php'); // SAFE: Allowlist pages $allowed = ['home', 'about']; include(in_array($page, $allowed) ? "$page.php" : 'home.php');

Watch for: == vs === , include/require , unserialize() , preg_replace with /e , extract()

Go

Main Risks: Race conditions, template injection, slice bounds

// UNSAFE: Race condition go func() { counter++ }() // SAFE: Use sync primitives atomic.AddInt64(&counter, 1)

// UNSAFE: Template injection template.HTML(userInput) // SAFE: Let template escape {{.UserInput}}

Watch for: Goroutine data races, template.HTML() , unsafe package, unchecked slice access

Ruby

Main Risks: Mass assignment, YAML deserialization, regex DoS

UNSAFE: Mass assignment

User.new(params[:user])

SAFE: Strong parameters

User.new(params.require(:user).permit(:name, :email))

UNSAFE: YAML RCE

YAML.load(user_input)

SAFE: Use safe_load

YAML.safe_load(user_input)

Watch for: YAML.load, Marshal.load, eval, send with user input, .permit!

Rust

Main Risks: Unsafe blocks, FFI boundary issues, integer overflow in release

// CAUTION: Unsafe bypasses safety unsafe { ptr::read(user_ptr) }

// CAUTION: Release integer overflow let x: u8 = 255; let y = x + 1; // Wraps to 0 in release! // SAFE: Use checked arithmetic let y = x.checked_add(1).unwrap_or(255);

Watch for: unsafe blocks, FFI calls, integer overflow in release builds, .unwrap() on untrusted input

Swift

Main Risks: Force unwrapping crashes, Objective-C interop

// UNSAFE: Force unwrap on untrusted data let value = jsonDict["key"]! // SAFE: Safe unwrapping guard let value = jsonDict["key"] else { return }

// UNSAFE: Format string String(format: userInput, args) // SAFE: Don't use user input as format

Watch for: force unwrap (!), try!, ObjC bridging, NSSecureCoding misuse

Kotlin

Main Risks: Null safety bypass, Java interop, serialization

// UNSAFE: Platform type from Java val len = javaString.length // NPE if null // SAFE: Explicit null check val len = javaString?.length ?: 0

// UNSAFE: Reflection clazz.getDeclaredMethod(userInput) // SAFE: Allowlist methods

Watch for: Java interop nulls (! operator), reflection, serialization, platform types

C / C++

Main Risks: Buffer overflow, use-after-free, format string

// UNSAFE: Buffer overflow char buf[10]; strcpy(buf, userInput); // SAFE: Bounds checking strncpy(buf, userInput, sizeof(buf) - 1);

// UNSAFE: Format string printf(userInput); // SAFE: Always use format specifier printf("%s", userInput);

Watch for: strcpy , sprintf , gets , pointer arithmetic, manual memory management, integer overflow

Scala

Main Risks: XML external entities, serialization, pattern matching exhaustiveness

// UNSAFE: XXE val xml = XML.loadString(userInput) // SAFE: Disable external entities val factory = SAXParserFactory.newInstance() factory.setFeature("http://xml.org/sax/features/external-general-entities", false)

Watch for: Java interop issues, XML parsing, Serializable , exhaustive pattern matching

R

Main Risks: Code injection, file path manipulation

UNSAFE: eval injection

eval(parse(text = user_input))

SAFE: Never parse user input as code

UNSAFE: Path traversal

read.csv(paste0("data/", user_file))

SAFE: Validate filename

if (grepl("^[a-zA-Z0-9]+\.csv$", user_file)) read.csv(...)

Watch for: eval() , parse() , source() , system() , file path manipulation

Perl

Main Risks: Regex injection, open() injection, taint mode bypass

UNSAFE: Regex DoS

$input =~ /$user_pattern/;

SAFE: Use quotemeta

$input =~ /\Q$user_pattern\E/;

UNSAFE: open() command injection

open(FILE, $user_file);

SAFE: Three-argument open

open(my $fh, '<', $user_file);

Watch for: Two-arg open() , regex from user input, backticks, eval , disabled taint mode

Shell (Bash)

Main Risks: Command injection, word splitting, globbing

UNSAFE: Unquoted variables

rm $user_file

SAFE: Always quote

rm "$user_file"

UNSAFE: eval

eval "$user_command"

SAFE: Never eval user input

Watch for: Unquoted variables, eval , backticks, $(...) with user input, missing set -euo pipefail

Lua

Main Risks: Sandbox escape, loadstring injection

-- UNSAFE: Code injection loadstring(user_code)() -- SAFE: Use sandboxed environment with restricted functions

Watch for: loadstring , loadfile , dofile , os.execute , io library, debug library

Elixir

Main Risks: Atom exhaustion, code injection, ETS access

UNSAFE: Atom exhaustion DoS

String.to_atom(user_input)

SAFE: Use existing atoms only

String.to_existing_atom(user_input)

UNSAFE: Code injection

Code.eval_string(user_input)

SAFE: Never eval user input

Watch for: String.to_atom , Code.eval_string , :erlang.binary_to_term , ETS public tables

Dart / Flutter

Main Risks: Platform channel injection, insecure storage

// UNSAFE: Storing secrets in SharedPreferences prefs.setString('auth_token', token); // SAFE: Use flutter_secure_storage secureStorage.write(key: 'auth_token', value: token);

Watch for: Platform channel data, dart:mirrors , Function.apply , insecure local storage

PowerShell

Main Risks: Command injection, execution policy bypass

UNSAFE: Injection

Invoke-Expression $userInput

SAFE: Avoid Invoke-Expression with user data

UNSAFE: Unvalidated path

Get-Content $userPath

SAFE: Validate path is within allowed directory

Watch for: Invoke-Expression , & $userVar , Start-Process with user args, -ExecutionPolicy Bypass

SQL (All Dialects)

Main Risks: Injection, privilege escalation, data exfiltration

-- UNSAFE: String concatenation "SELECT * FROM users WHERE id = " + userId

-- SAFE: Parameterized query (language-specific) -- Use prepared statements in ALL cases

Watch for: Dynamic SQL, EXECUTE IMMEDIATE , stored procedures with dynamic queries, privilege grants

Deep Security Analysis Mindset

When reviewing any language, think like a senior security researcher:

• Memory Model: How does the language handle memory? Managed vs manual? GC pauses exploitable?

• Type System: Weak typing = type confusion attacks. Look for coercion exploits.

• Serialization: Every language has its pickle/Marshal equivalent. All are dangerous.

• Concurrency: Race conditions, TOCTOU, atomicity failures specific to the threading model.

• FFI Boundaries: Native interop is where type safety breaks down.

• Standard Library: Historic CVEs in std libs (Python urllib, Java XML, Ruby OpenSSL).

• Package Ecosystem: Typosquatting, dependency confusion, malicious packages.

• Build System: Makefile/gradle/npm script injection during builds.

• Runtime Behavior: Debug vs release differences (Rust overflow, C++ assertions).

• Error Handling: How does the language fail? Silently? With stack traces? Fail-open?

For any language not listed: Research its specific CWE patterns, CVE history, and known footguns. The examples above are entry points, not complete coverage.

When to Apply This Skill

Use this skill when:

• Writing authentication or authorization code

• Handling user input or external data

• Implementing cryptography or password storage

• Reviewing code for security vulnerabilities

• Designing API endpoints

• Building AI agent systems

• Configuring application security settings

• Handling errors and exceptions

• Working with third-party dependencies

• Working in any language - apply the deep analysis mindset above