CVE-2026-16240: Use of externally-controlled format string in PostgreSQL pg_basebackup allows an attacker having already compromised a server to achieve disclosure from pg_base

Use of externally-controlled format string in PostgreSQL pg_basebackup allows an attacker having already compromised a server to achieve disclosure from pg_basebackup memory, via backup manifest bytes. The vulnerability does not return the improperly-read bytes back to the attacker's server, so a successful attack would need separate implementation-specific secrets for that. Integrity impact is unlikely; in particular, the applicable formatter does not support %n. Versions before PostgreSQL 1