Reject substituting extension schemas or owners matching ["$'\].

Substituting such values in extension scripts facilitated SQL injection
when @extowner@, @extschema@, or @extschema:...@ appeared inside a
quoting construct (dollar quoting, '', or "").  No bundled extension was
vulnerable.  Vulnerable uses do appear in a documentation example and in
non-bundled extensions.  Hence, the attack prerequisite was an
administrator having installed files of a vulnerable, trusted,
non-bundled extension.  Subject to that prerequisite, this enabled an
attacker having database-level CREATE privilege to execute arbitrary
code as the bootstrap superuser.  By blocking this attack in the core
server, there's no need to modify individual extensions.  Back-patch to
v11 (all supported versions).

Reported by Micah Gate, Valerie Woolard, Tim Carey-Smith, and Christoph
Berg.

Security: CVE-2023-39417

1 files changed, 16 insertions, 0 deletions

diff --git a/src/backend/commands/extension.c b/src/backend/commands/extension.c
index 7e81d848190..0f9edf68c3a 100644
--- a/src/backend/commands/extension.c
+++ b/src/backend/commands/extension.c
@@ -888,6 +888,16 @@ execute_extension_script(Oid extensionOid, ExtensionControlFile *control,
 		char	   *c_sql = read_extension_script_file(control, filename);
 		Datum		t_sql;
 
+		/*
+		 * We filter each substitution through quote_identifier().  When the
+		 * arg contains one of the following characters, no one collection of
+		 * quoting can work inside $$dollar-quoted string literals$$,
+		 * 'single-quoted string literals', and outside of any literal.  To
+		 * avoid a security snare for extension authors, error on substitution
+		 * for arguments containing these.
+		 */
+		const char *quoting_relevant_chars = "\"$'\\";
+
 		/* We use various functions that want to operate on text datums */
 		t_sql = CStringGetTextDatum(c_sql);
 
@@ -912,6 +922,7 @@ execute_extension_script(Oid extensionOid, ExtensionControlFile *control,
 		 */
 		if (!control->relocatable)
 		{
+			Datum		old = t_sql;
 			const char *qSchemaName = quote_identifier(schemaName);
 
 			t_sql = DirectFunctionCall3Coll(replace_text,
@@ -919,6 +930,11 @@ execute_extension_script(Oid extensionOid, ExtensionControlFile *control,
 											t_sql,
 											CStringGetTextDatum("@extschema@"),
 											CStringGetTextDatum(qSchemaName));
+			if (t_sql != old && strpbrk(schemaName, quoting_relevant_chars))
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
+						 errmsg("invalid character in extension \"%s\" schema: must not contain any of \"%s\"",
+								control->name, quoting_relevant_chars)));
 		}
 
 		/*