SSL/TLS Downgrade Attack.

An active man-in-the-middle attack that forces a client and server to negotiate a weaker protocol version, cipher, or key size to enable further compromise. It belongs to the Attacks & Threats category of cybersecurity.

An active man-in-the-middle attack that forces a client and server to negotiate a weaker protocol version, cipher, or key size to enable further compromise.

An SSL/TLS downgrade attack manipulates the ClientHello or ServerHello of the handshake so that endpoints settle on a vulnerable parameter set. Examples include POODLE (forcing SSL 3.0 to exploit its CBC padding), FREAK (negotiating RSA_EXPORT), Logjam (DHE_EXPORT 512-bit groups), and version downgrade dances that strip TLS 1.2 hints. Once weakened, the connection becomes vulnerable to known cryptanalysis or key recovery. Defenses include disabling legacy protocols (SSLv2/3, TLS 1.0/1.1) and weak ciphersuites, enforcing TLS 1.2/1.3, supporting the TLS_FALLBACK_SCSV signaling cipher, deploying HSTS, and TLS 1.3's handshake transcript binding which makes silent downgrades detectable.

Defences for SSL/TLS Downgrade Attack typically combine technical controls and operational practices, as detailed in the full definition above.

Common alternative names include: Protocol downgrade, Cipher downgrade.