The PostgreSQL JDBC Driver (pgJDBC) versions 42.7.4 through 42.7.11 are vulnerable to a silent downgrade of channel-binding authentication from SCRAM-SHA-256-PLUS (which includes channel binding) to SCRAM-SHA-256 (without channel binding). This occurs when the TLS server certificate uses signature algorithms without a tls-server-end-point channel-binding hash (e.g., Ed25519, Ed448, or post-quantum algorithms). The scram-client library bundled with these versions returns an empty byte array instead of failing when it cannot derive the binding hash. Additionally, pgJDBC does not enforce channel binding after negotiation, allowing the downgrade to succeed silently. Only connections explicitly setting channelBinding=require are affected; other policies behave as documented. The issue is resolved in pgJDBC 42.7.12, which enforces channel binding strictly and fails connections lacking valid channel-binding data. No pgJDBC configuration can restore enforcement on affected versions, so upgrading is necessary. Independent TLS certificate verification can mitigate the risk by preventing man-in-the-middle attacks presenting substitute certificates.

Connections using channelBinding=require lose the man-in-the-middle protection provided by SCRAM-SHA-256-PLUS authentication due to silent downgrade to SCRAM-SHA-256 without channel binding. This weakens authentication security against attackers intercepting TLS connections who can present certificates with unsupported signature algorithms. The vulnerability affects only pgJDBC versions 42.7.4 through 42.7.11 and only when channelBinding=require is set. Default or other channel binding policies are not vulnerable to this downgrade. The impact is a loss of intended channel-binding security guarantees, increasing risk of credential interception or session hijacking in affected configurations.

Upgrade pgJDBC to version 42.7.12 or later, which enforces channel binding correctly and fails connections lacking valid channel-binding data. No configuration setting on affected versions can restore proper enforcement. If immediate upgrade is not possible, enforce strict TLS certificate verification by setting sslmode=verify-full and using a truststore containing only the server's CA certificate. This prevents man-in-the-middle attackers from presenting substitute certificates and mitigates the risk independently of channel binding. Connections relying solely on channelBinding=require without certificate verification have no effective workaround other than upgrading.