Authentication Failures Explained (OWASP A07) — 2026

Identification and authentication failures (#7 on the OWASP Top 10) cover the many ways login and session handling go wrong — letting attackers impersonate legitimate users. Since authentication is the front door, getting it wrong is catastrophic.

The core idea

Authentication proves who you are. If that proof can be guessed, stolen, bypassed, or reused, an attacker becomes you — no exploit required. (Note: authentication is "who are you"; authorization is "what can you do" — that's broken access control.)

Common failures

• Weak password policies — allowing trivial or common passwords.
• Credential stuffing — attackers reuse passwords leaked in other breaches; if your users reused theirs, they're in.
• Brute force — no rate limiting on login attempts.
• No MFA — a single stolen password = full access.
• Poor session management — predictable tokens, sessions that never expire, tokens exposed in URLs.
• Insecure password recovery — weak "forgot password" flows that are easier to attack than the login.

How to prevent it

1. Require MFA — the single highest-impact control. Even a phished password often fails without the second factor.
2. Enforce strong passwords — length over complexity; block known-breached passwords.
3. Rate-limit and lock out — stop brute force and credential stuffing.
4. Secure sessions — random, sufficiently long tokens; expire them; use HttpOnly + Secure cookies; rotate on login.
5. Harden recovery flows — they're a common bypass.
6. Use proven auth — frameworks/providers (OAuth/OIDC), not homegrown login code.

Why MFA is the headline

Most account takeovers trace back to passwords — guessed, reused, or phished. MFA breaks that chain. If you do one thing, do MFA everywhere.

How it's found

Testers probe for weak policies, missing rate limits, predictable sessions, and bypassable recovery — within an authorized pentest. These are logic-and-config issues, so both human and AI-driven testing help.

Related: Cryptographic Failures (how passwords should be stored). Learn authentication security free at the Pentevo Academy.