From 0119aa30e0fc78771681cc54e4133bf7bd3a77dd Mon Sep 17 00:00:00 2001
From: Nathan Bossart <nathan@postgresql.org>
Date: Mon, 10 Aug 2026 06:38:06 -0700
Subject: [PATCH] psql: Don't do backquote expansion in \unrestrict.

This oversight in commit 71ea0d6795 allows a malicious server to
inject shell commands into plain-text dump output that are run at
restore time on the machine running psql.  To fix, interpret all
text after \unrestrict until the end of the line as its argument.

Reported-by: Lucas Velgus <velgusgus599@gmail.com>
Reported-by: Filip Janus <fjanus@redhat.com>
Reported-by: Daniel Bakker <daniel@jackds.nl>
Author: Nathan Bossart <nathandbossart@gmail.com>
Reviewed-by: Robert Haas <robertmhaas@gmail.com>
Reviewed-by: Noah Misch <noah@leadboat.com>
Security: CVE-2026-18408
Backpatch-through: 14
---
 doc/src/sgml/ref/psql-ref.sgml |  5 +++++
 src/bin/psql/command.c         | 10 ++++++++--
 src/bin/psql/t/001_basic.pl    |  7 +++++++
 3 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/doc/src/sgml/ref/psql-ref.sgml b/doc/src/sgml/ref/psql-ref.sgml
index 844cd0d5d8b..6cb2f968f12 100644
--- a/doc/src/sgml/ref/psql-ref.sgml
+++ b/doc/src/sgml/ref/psql-ref.sgml
@@ -3859,6 +3859,11 @@ SELECT 1 \bind \sendpipeline
         <application>pg_dumpall</application>, and
         <application>pg_restore</application>, but it may be useful elsewhere.
         </para>
+        <para>
+        Unlike most other meta-commands, the entire remainder of the line is
+        always taken to be the argument of <command>\unrestrict</command>, and
+        neither variable interpolation nor backquote expansion are performed.
+        </para>
         </listitem>
       </varlistentry>
 
diff --git a/src/bin/psql/command.c b/src/bin/psql/command.c
index 027b8ab7ed0..fc5a0d4221f 100644
--- a/src/bin/psql/command.c
+++ b/src/bin/psql/command.c
@@ -2790,6 +2790,12 @@ exec_command_restrict(PsqlScanState scan_state, bool active_branch,
 
 		Assert(!restricted);
 
+		/*
+		 * Unlike \unrestrict, this argument may safely undergo backquote and
+		 * variable expansion: HandleSlashCmds() rejects \restrict in
+		 * restricted mode before its argument is scanned, so we only get here
+		 * when the input could execute such things anyway.
+		 */
 		opt = psql_scan_slash_option(scan_state, OT_NORMAL, NULL, true);
 		if (opt == NULL || opt[0] == '\0')
 		{
@@ -3198,7 +3204,7 @@ exec_command_unrestrict(PsqlScanState scan_state, bool active_branch,
 	{
 		char	   *opt;
 
-		opt = psql_scan_slash_option(scan_state, OT_NORMAL, NULL, true);
+		opt = psql_scan_slash_option(scan_state, OT_WHOLE_LINE, NULL, true);
 		if (opt == NULL || opt[0] == '\0')
 		{
 			pg_log_error("\\%s: missing required argument", cmd);
@@ -3222,7 +3228,7 @@ exec_command_unrestrict(PsqlScanState scan_state, bool active_branch,
 		}
 	}
 	else
-		ignore_slash_options(scan_state);
+		ignore_slash_whole_line(scan_state);
 
 	return PSQL_CMD_SKIP_LINE;
 }
diff --git a/src/bin/psql/t/001_basic.pl b/src/bin/psql/t/001_basic.pl
index bbd330216ae..04644f2fdfc 100644
--- a/src/bin/psql/t/001_basic.pl
+++ b/src/bin/psql/t/001_basic.pl
@@ -540,4 +540,11 @@ psql_fails_like(
 	qr/backslash commands are restricted; only \\unrestrict is allowed/,
 	'meta-command in restrict mode fails');
 
+psql_fails_like(
+	$node,
+	qq{\\restrict test
+\\unrestrict `echo test`},
+	qr/wrong key/,
+	'\unrestrict does not do backquote expansion');
+
 done_testing();