Affected: Progressive Robot Ltd hMailServer

Misinterpretation of SQL statement text in the database layer of Progressive Robot hMailServer 6.0.0-B1 through 6.3.7 allows a remote unauthenticated attacker to have a failed database write reported to the server as successful. The layer answers a failed statement as a success when it finds the marker [IGNORE-ERRORS], which is meant only for the server's own schema statements (its upgrade scripts and the database log's tables), and statements carry values from outside - an envelope address, the user name of a failed logon, a message's headers - in their text on MySQL/MariaDB and PostgreSQL, and in the batches of the database log on every engine. Up to 6.2.18 the marker was honoured anywhere in a statement, a value included, on MySQL/MariaDB and PostgreSQL. From 6.2.19 it was honoured only inside a comment, but the layer read a backslash inside a string literal as an escape, which SQL Server, SQL Server Compact and PostgreSQL with standard_conforming_strings on (its default) do not, so that on those engines a value holding a backslash could make the layer take part of the statement's literals for statement text and find the marker there: on PostgreSQL from 6.3.3 for every statement carrying an outside value that holds a backslash, with no setting changed for a message delivered into a local mailbox (through an internationalised (SMTPUTF8) envelope sender) and for the IP range an auto-ban writes (named after the user name of the failed logon), and on SQL Server and SQL Server…