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The recursion in cdissect() was careless about clearing match data for capturing parentheses after rejecting a partial match. This could allow a later back-reference to succeed when by rights it should fail for lack of a defined referent. To fix, think a little more rigorously about what the contract between different levels of cdissect's recursion needs to be. With the right spec, we can fix this using fewer rather than more resets of the match data; the key decision being that a failed sub-match is now explicitly responsible for clearing any matches it may have set. There are enough other cross-checks and optimizations in the code that it's not especially easy to exhibit this problem; usually, the match will fail as-expected. Plus, regexps that are even potentially vulnerable are most likely user errors, since there's just not much point in writing a back-ref that doesn't always have a referent. These facts perhaps explain why the issue hasn't been detected, even though it's almost certainly a couple of decades old. Discussion: https://postgr.es/m/151435.1629733387@sss.pgh.pa.us
PostgreSQL Database Management System ===================================== This directory contains the source code distribution of the PostgreSQL database management system. PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings. PostgreSQL has many language interfaces, many of which are listed here: https://www.postgresql.org/download/ See the file INSTALL for instructions on how to build and install PostgreSQL. That file also lists supported operating systems and hardware platforms and contains information regarding any other software packages that are required to build or run the PostgreSQL system. Copyright and license information can be found in the file COPYRIGHT. A comprehensive documentation set is included in this distribution; it can be read as described in the installation instructions. The latest version of this software may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.