Medium [CVE-2026-54291] Man-in-the-middle protection bypass via SCRAM-SHA-256-PLUS downgrade

pgjdbc is an open source postgresql JDBC Driver. In releases 42.7.4 through 42.7.11, channelBinding=require connections can be silently downgraded from SCRAM-SHA-256-PLUS with channel binding to plain SCRAM-SHA-256 without it, losing the man-in-the-middle protection the setting is meant to guarantee.

An attacker who can intercept the TLS connection can trigger the downgrade with a certificate whose signature algorithm has no tls-server-end-point channel-binding hash, because the bundled com.ongres.scram:scram-client returns an empty byte array instead of failing and pgJDBC ScramAuthenticator checks only that the server advertised a PLUS mechanism, without rejecting the empty binding or checking that the negotiated mechanism uses channel binding.

This issue is fixed in version 42.7.12. A remote attacker who can intercept a TLS (Transport Layer Security) connection can silently downgrade connections configured to require channel binding from SCRAM-SHA-256-PLUS to plain SCRAM-SHA-256.

This downgrade bypasses the intended man-in-the-middle protection, allowing the attacker to potentially intercept or alter sensitive communication. The vulnerability occurs because the system fails to properly validate the channel binding when a specific type of certificate is used.

Red Hat severity: Moderate — CVSS 5.9 (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N). Weakness: CWE-940.