POSTGRESQL has issued a security fix for a 12-year-old flaw that could enable a replication account to run arbitrary code as the operating-system user running the database server. Tracked as CVE-2026-6471 (CVSS 7.2), the vulnerability has been present since logical decoding was introduced in PostgreSQL 9.4 in 2014 and affects releases prior to 18.6, 17.11, 16.15, 15.19, and 14.24.
The problem arises because a REPLICATION role can specify a loadable library for logical decoding without the usual path restrictions, which in practice allowed exploitation via backup tools, standby servers, CDC pipelines and similar setups that carry the REPLICATION attribute. Cyera’s research described the flaw as PostGREShell, with evidence that a crafted CREATE_REPLICATION_SLOT command could pass a library name to the loader, bypassing prior protections.
The fix, shipped on 13 August, introduces a new server parameter called output_plugin_libraries, which acts as a whitelist of allowed logical decoding output plugins. By default it permits pgoutput and test_decoding; any other plugin, such as wal2json or decoderbufs, will be refused until an administrator adds the library to the list and reloads the configuration.
Administrators are advised to identify currently used plugins with a SELECT DISTINCT plugin FROM pg_replication_slots WHERE plugin IS NOT NULL; upgrade to the fixed releases (18.6, 17.11, 16.15, 15.19, or 14.24 or their distribution equivalents); and then add non-default plugins to output_plugin_libraries and reload with pg_ctl reload or pg_reload_conf. A restart is not required.
As of 4 September 2026, PostgreSQL notes, advice and patches cover supported branches 14–18, with some distribution advisories flagging additional configuration changes when extensions are involved. In the meantime, Cyera recommends removing the REPLICATION attribute where unnecessary and restricting replication entries, among other mitigations.