Backport of:

From 4130b022fa5da8994908816302942a7591acea7e Mon Sep 17 00:00:00 2001
From: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Date: Sat, 2 May 2026 22:14:43 +1200
Subject: [PATCH 24/27] CVE-2026-4408: s3:torture: tests for password
 complexity scripts

This tries to demonstrate the new logic for %u in
'check password script'.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=16034

Pair-Programmed-With: Stefan Metzmacher <metze@samba.org>

Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Signed-off-by: Stefan Metzmacher <metze@samba.org>
---
 selftest/tests.py               |   2 +
 source3/torture/test_rpc_samr.c | 358 ++++++++++++++++++++++++++++++++
 source3/torture/wscript_build   |   6 +
 3 files changed, 366 insertions(+)
 create mode 100644 source3/torture/test_rpc_samr.c

--- a/selftest/tests.py
+++ b/selftest/tests.py
@@ -433,6 +433,8 @@ plantestsuite("samba.unittests.test_regi
               [os.path.join(bindir(), "default/source3/test_registry_regfio")])
 plantestsuite("samba.unittests.test_oLschema2ldif", "none",
               [os.path.join(bindir(), "default/source4/utils/oLschema2ldif/test_oLschema2ldif")])
+plantestsuite("samba.unittests.test_rpc_samr", "none",
+              [os.path.join(bindir(), "test_rpc_samr")])
 if have_heimdal_support and not using_system_gssapi:
     plantestsuite("samba.unittests.auth.heimdal_gensec_unwrap_des", "none",
               [valgrindify(os.path.join(bindir(), "test_heimdal_gensec_unwrap_des"))])
--- /dev/null
+++ b/source3/torture/test_rpc_samr.c
@@ -0,0 +1,358 @@
+
+#include <stdarg.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <setjmp.h>
+#include <sys/stat.h>
+#include <cmocka.h>
+#include "includes.h"
+#include "talloc.h"
+#include "libcli/util/ntstatus.h"
+#include "../librpc/gen_ndr/samr.h"
+#include "rpc_server/samr/srv_samr_util.h"
+
+/* set SAMR_DEBUG_VERBOSE to true to print more. */
+#define SAMR_DEBUG_VERBOSE true
+
+#if SAMR_DEBUG_VERBOSE
+#define debug_message(...) print_message(__VA_ARGS__)
+#else
+#define debug_message(...) /* debug_message */
+#endif
+
+static int setup_talloc_context(void **state)
+{
+	TALLOC_CTX *mem_ctx = talloc_new(NULL);
+	*state = mem_ctx;
+	return 0;
+}
+
+static int teardown_talloc_context(void **state)
+{
+	TALLOC_CTX *mem_ctx = *state;
+	TALLOC_FREE(mem_ctx);
+	return 0;
+}
+
+struct cmd_expansion {
+	const char *lp_cmd;
+	const char *username;
+	const char *result_cmd;
+	NTSTATUS result_code;
+};
+
+static struct cmd_expansion expansions[] = {
+	{
+		"/bin/echo '%u'",
+		"bob",
+		"/bin/echo 'bob'",
+		NT_STATUS_OK
+	},
+	{
+		"/bin/echo %u",
+		"bob",
+		"/bin/echo 'bob'",
+		NT_STATUS_OK
+	},
+	{
+		"/bin/echo %u",
+		"bob'",
+		"/bin/echo 'bob_'",
+		NT_STATUS_OK
+	},
+	{
+		"/bin/echo %u",
+		"bob\'",
+		"/bin/echo 'bob_'",
+		NT_STATUS_OK
+	},
+	{
+		"/bin/echo %u",
+		"bob'''",
+		"/bin/echo 'bob___'",
+		NT_STATUS_OK
+	},
+	{
+		"/bin/echo %u",
+		"bob*",
+		NULL,
+		NT_STATUS_INVALID_USER_PRINCIPAL_NAME
+	},
+	{
+		"/bin/echo %u",
+		"bob\"",
+		NULL,
+		NT_STATUS_INVALID_USER_PRINCIPAL_NAME
+	},
+	{
+		"/bin/echo '%u",
+		"bob bob bob",
+		"/bin/echo '__CVE-2026-4408_FallbackUsername__",
+		NT_STATUS_OK
+	},
+	{
+		"/bin/echo \"%u\"",
+		" ",
+		"/bin/echo ' '",
+		NT_STATUS_OK
+	},
+	{
+		"/bin/echo \"--uu=%u\"",
+		"bob",
+		"/bin/echo \"--uu=__CVE-2026-4408_FallbackUsername__\"",
+		NT_STATUS_OK
+	},
+	{
+		"/bin/echo \"--uu=%u\"",
+		"bob !0",
+		"/bin/echo \"--uu=__CVE-2026-4408_FallbackUsername__\"",
+		NT_STATUS_OK
+	},
+	{
+		"/bin/echo %u",
+		"!0",
+		"/bin/echo '!0'",
+		NT_STATUS_OK
+	},
+	{
+		"/bin/echo \"--uu=%u\"",
+		"bob \\",
+		NULL,
+		NT_STATUS_INVALID_USER_PRINCIPAL_NAME
+	},
+	{
+		"/bin/echo --uu='%u'",
+		"bob >> x",
+		NULL,
+		NT_STATUS_INVALID_USER_PRINCIPAL_NAME
+	},
+	{
+		"/bin/echo '--uu=%u\"",
+		"bob",
+		"/bin/echo '--uu=__CVE-2026-4408_FallbackUsername__\"",
+		NT_STATUS_OK
+	},
+	{
+		"/bin/echo --uu='%u'",
+		"bob",
+		"/bin/echo --uu='bob'",
+		NT_STATUS_OK
+	},
+	{
+		"/bin/echo --uu'=%u'",
+		"bob",
+		"/bin/echo --uu'=__CVE-2026-4408_FallbackUsername__'",
+		NT_STATUS_OK
+	},
+	{
+		"/bin/echo --uu'=%u'",
+		"`ls`",
+		"/bin/echo --uu'=__CVE-2026-4408_FallbackUsername__'",
+		NT_STATUS_OK
+	},
+	{
+		"/bin/echo --uu'=%u'",
+		"$(ls)",
+		"/bin/echo --uu'=__CVE-2026-4408_FallbackUsername__'",
+		NT_STATUS_OK
+	},
+	{
+		"/bin/echo --uu='%u'",
+		"$(ls)",
+		"/bin/echo --uu='_(ls)'",
+		NT_STATUS_OK
+	},
+	{
+		"/bin/echo --uu=\"'%u'\"",
+		"bob",
+		"/bin/echo --uu=\"'bob'\"",
+		NT_STATUS_OK
+	},
+	{
+		"/bin/echo --uu='%u' --yy='%u' '%u' %u",
+		"bob",
+		"/bin/echo --uu='bob' --yy='bob' 'bob' __CVE-2026-4408_FallbackUsername__",
+		NT_STATUS_OK
+	},
+	{
+		"/bin/echo --uu=%u%u'' %user 50%u",
+		"bob",
+		"/bin/echo --uu=__CVE-2026-4408_FallbackUsername____CVE-2026-4408_FallbackUsername__'' __CVE-2026-4408_FallbackUsername__ser 50__CVE-2026-4408_FallbackUsername__",
+		NT_STATUS_OK
+	},
+	{
+		"/bin/echo %u",
+		"!!",
+		"/bin/echo '!!'",
+		NT_STATUS_OK
+	},
+	{
+		"/bin/echo %u",
+		">xxx",
+		NULL,
+		NT_STATUS_INVALID_USER_PRINCIPAL_NAME
+	},
+	{
+		"/bin/echo %u",
+		"\\",
+		NULL,
+		NT_STATUS_INVALID_USER_PRINCIPAL_NAME
+	},
+	{
+		"/bin/echo %u",
+		"3",
+		"/bin/echo '3'",
+		NT_STATUS_OK
+	},
+	{
+		"/bin/echo '%u'",
+		"3$",
+		"/bin/echo '3_'",
+		NT_STATUS_OK
+	},
+	{
+		"/bin/echo '%u'",
+		"comp$",
+		"/bin/echo 'comp_'",
+		NT_STATUS_OK
+	},
+	{
+		"/bin/echo '%u'",
+		"3$3",
+		"/bin/echo '3_3'",
+		NT_STATUS_OK
+	},
+	{
+		"/bin/echo '%u'",
+		"q $3",
+		"/bin/echo 'q _3'",
+		NT_STATUS_OK
+	},
+	{
+		"/bin/echo -s '%u' %u",
+		"āāā",
+		"/bin/echo -s 'āāā' __CVE-2026-4408_FallbackUsername__",
+		NT_STATUS_OK
+	},
+	{
+		"/bin/echo -s '%u' %u",
+		"-āāā",
+		"/bin/echo -s '_āāā' __CVE-2026-4408_FallbackUsername__",
+		NT_STATUS_OK
+	},
+	{
+		"/bin/echo -s %u",
+		"āāā",
+		"/bin/echo -s 'āāā'",
+		NT_STATUS_OK
+	},
+	{
+		"/bin/echo -s %u",
+		"a -a",
+		"/bin/echo -s 'a -a'",
+		NT_STATUS_OK
+	},
+	{
+		"/bin/echo -s=%u %u",
+		"ā -a",
+		"/bin/echo -s='ā -a' 'ā -a'",
+		NT_STATUS_OK
+	},
+	{
+		"/bin/echo -s=\"%u %u\"",
+		"ā -a",
+		"/bin/echo -s=\"__CVE-2026-4408_FallbackUsername__ __CVE-2026-4408_FallbackUsername__\"",
+		NT_STATUS_OK
+	},
+	{
+		"/bin/echo -m='fridge' %u",
+		"ā -x -ß",
+		"/bin/echo -m='fridge' __CVE-2026-4408_FallbackUsername__",
+		NT_STATUS_OK
+	},
+	{
+		"/bin/echo -m='fridge' %u",
+		"-ā -a",
+		"/bin/echo -m='fridge' __CVE-2026-4408_FallbackUsername__",
+		NT_STATUS_OK
+	},
+	{
+		"/bin/echo %u",
+		"-n",
+		"/bin/echo '_n'",
+		NT_STATUS_OK
+	},
+	{
+		"/bin/echo %u",
+		"o'clock",
+		"/bin/echo 'o_clock'",
+		NT_STATUS_OK
+	},
+};
+
+static void test_expansions(void **state)
+{
+	TALLOC_CTX *mem_ctx = *state;
+	size_t i;
+
+	for (i = 0; i < ARRAY_SIZE(expansions); i++) {
+		struct cmd_expansion t = expansions[i];
+		char *result_cmd = NULL;
+		NTSTATUS status;
+
+		status = check_password_complexity_internal(mem_ctx,
+							    t.lp_cmd,
+							    t.username,
+							    &result_cmd);
+		if (NT_STATUS_IS_OK(t.result_code) && NT_STATUS_IS_OK(status)) {
+			int cmp;
+
+			cmp = strcmp(t.result_cmd, result_cmd);
+			if (cmp == 0) {
+				debug_message("[%zu] «%s» «%s»   ->   «%s», nstatus %s; AS EXPECTED\n",
+					      i, t.lp_cmd,
+					      t.username,
+					      result_cmd,
+					      nt_errstr(status));
+			} else {
+				debug_message("[%zu] «%s» «%s», nstatus %s; "
+					      "expected   «%s»   got  «%s»\033[1;31m BAD! \033[0m\n",
+					      i, t.lp_cmd,
+					      t.username,
+					      nt_errstr(status),
+					      t.result_cmd,
+					      result_cmd);
+			}
+			assert_int_equal(cmp, 0);
+		} else if (NT_STATUS_EQUAL(status, t.result_code)) {
+			debug_message("[%zu] «%s» «%s», nstatus %s FAILED AS EXPECTED\n",
+				      i, t.lp_cmd,
+				      t.username,
+				      nt_errstr(status));
+		} else {
+			debug_message("[%zu] «%s» «%s» -> «%s», nstatus %s; "
+				      "EXPECTED result «%s»   ntstatus %s; \033[1;31m BAD! \033[0m\n",
+				      i, t.lp_cmd,
+				      t.username,
+				      result_cmd,
+				      nt_errstr(status),
+				      t.result_cmd,
+				      nt_errstr(t.result_code));
+			assert_int_equal(true, false);
+		}
+	}
+	debug_message("ALL correct\n");
+}
+
+int main(void)
+{
+	const struct CMUnitTest tests[] = {
+		cmocka_unit_test(test_expansions),
+	};
+	if (!isatty(1)) {
+		cmocka_set_message_output(CM_OUTPUT_SUBUNIT);
+	}
+	return cmocka_run_group_tests(tests,
+				      setup_talloc_context,
+				      teardown_talloc_context);
+}
