Common TLS Attacks

Because TLS protects so much traffic, attackers constantly look for weaknesses.

Most attacks try to downgrade security, strip encryption, or exploit old protocol flaws.

In a downgrade attack, an attacker interferes with the handshake to force both sides onto an older, weaker protocol or cipher.

The POODLE attack abused a forced downgrade to SSL 3.0.

Defenses include:

• Disabling old protocols (SSL 2/3, TLS 1.0/1.1).
• The TLS downgrade protection built into TLS 1.3.
• The SCSV fallback signal in TLS 1.2.

SSL stripping happens when a user types a plain http:// link. A man-in-the-middle keeps the connection unencrypted toward the user while talking HTTPS to the server.

The victim never sees the lock icon, often unnoticed.

HTTP Strict Transport Security (HSTS) tells browsers to always use HTTPS for a domain, blocking stripping.

A man-in-the-middle (MITM) sits between client and server, relaying traffic.

Proper certificate validation defeats this: the attacker cannot present a valid certificate for the target domain that a trusted CA signed.

CRIME and BREACH exploited TLS or HTTP compression to leak secrets like session cookies by observing compressed response sizes.

The fix: disable TLS compression and be careful mixing secrets with attacker-controlled data.

Old CBC-mode ciphers were vulnerable to padding oracle attacks like Lucky 13.

Modern AEAD ciphers (AES-GCM, ChaCha20-Poly1305) eliminate this entire class of bugs.

Heartbleed was a memory-disclosure bug in OpenSSL, not a TLS protocol flaw. It let attackers read server memory, potentially leaking private keys.

Lesson: keep your TLS libraries patched.

Older TLS allowed unsafe renegotiation and truncation attacks where injected data or cut-off messages could be abused.

Secure renegotiation extensions and TLS 1.3 address these.

To harden TLS:

• Use only TLS 1.2 and 1.3.
• Prefer AEAD cipher suites with forward secrecy.
• Enable HSTS.
• Disable compression.
• Keep libraries patched.

Which defense specifically prevents SSL stripping attacks?

You learned about common TLS attacks.

• Downgrade and stripping force weaker or no encryption.
• HSTS and disabling old protocols are key defenses.
• AEAD ciphers and patching kill padding-oracle and library bugs.

Next module: Multi-Factor Authentication.