From 75661a66a1db1e1f3f1245c615f13a7de44c0587 Mon Sep 17 00:00:00 2001
From: Christian Brabandt <cb@256bit.org>
Date: Tue, 31 Mar 2026 18:29:00 +0000
Subject: [PATCH] patch 9.2.0276: [security]: modeline security bypass

Problem:  [security]: modeline security bypass
Solution: disallow mapset() from secure mode, set the P_MLE flag for the
          'complete', 'guitabtooltip' and 'printheader' options.

Github Advisory:
https://github.com/vim/vim/security/advisories/GHSA-8h6p-m6gr-mpw9

Signed-off-by: Christian Brabandt <cb@256bit.org>

Backported for vim 9.1.083
---
 src/map.c                     |  3 +++
 src/optiondefs.h              |  6 +++---
 src/testdir/test_modeline.vim | 25 +++++++++++++++++++++++++
 3 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/src/map.c b/src/map.c
index 0a909fb93b2e4..5f07ef4a81433 100644
--- a/src/map.c
+++ b/src/map.c
@@ -2708,6 +2708,9 @@ f_mapset(typval_T *argvars, typval_T *rettv UNUSED)
     char_u	*arg;
     int		dict_only;

+    if (check_secure())
+	return;
+
     // If first arg is a dict, then that's the only arg permitted.
     dict_only = argvars[0].v_type == VAR_DICT;
     if (in_vim9script()
diff --git a/src/optiondefs.h b/src/optiondefs.h
index ca2795a364b66..a6f8383084285 100644
--- a/src/optiondefs.h
+++ b/src/optiondefs.h
@@ -639,7 +639,7 @@ static struct vimoption options[] =
     {"compatible",  "cp",   P_BOOL|P_RALL,
 			    (char_u *)&p_cp, PV_NONE, did_set_compatible, NULL,
 			    {(char_u *)TRUE, (char_u *)FALSE} SCTX_INIT},
-    {"complete",    "cpt",  P_STRING|P_ALLOCED|P_VI_DEF|P_ONECOMMA|P_NODUP,
+    {"complete",    "cpt",  P_STRING|P_ALLOCED|P_VI_DEF|P_ONECOMMA|P_NODUP|P_MLE,
 			    (char_u *)&p_cpt, PV_CPT, did_set_complete, expand_set_complete,
 			    {(char_u *)".,w,b,u,t,i", (char_u *)0L}
 			    SCTX_INIT},
@@ -1251,7 +1251,7 @@ static struct vimoption options[] =
 			    {(char_u *)NULL, (char_u *)0L}
 #endif
 			    SCTX_INIT},
-    {"guitabtooltip",  "gtt", P_STRING|P_VI_DEF|P_RWIN,
+    {"guitabtooltip",  "gtt", P_STRING|P_VI_DEF|P_RWIN|P_MLE,
 #if defined(FEAT_GUI_TABLINE)
 			    (char_u *)&p_gtt, PV_NONE, NULL, NULL,
 			    {(char_u *)"", (char_u *)0L}
@@ -1950,7 +1950,7 @@ static struct vimoption options[] =
 			    {(char_u *)NULL, (char_u *)0L}
 #endif
 			    SCTX_INIT},
-    {"printheader", "pheader",  P_STRING|P_VI_DEF|P_GETTEXT,
+    {"printheader", "pheader",  P_STRING|P_VI_DEF|P_GETTEXT|P_MLE,
 #ifdef FEAT_PRINTER
 			    (char_u *)&p_header, PV_NONE, NULL, NULL,
 			    // untranslated to avoid problems when 'encoding'
diff --git a/src/testdir/test_modeline.vim b/src/testdir/test_modeline.vim
index 4cc091b9ca586..25ca6fb437003 100644
--- a/src/testdir/test_modeline.vim
+++ b/src/testdir/test_modeline.vim
@@ -469,4 +469,29 @@ func Test_modeline_disable()
   call assert_equal(2, &sw)
 endfunc

+func Test_modeline_forbidden()
+  let tempfile = tempname()
+  let lines =<< trim END
+    some test text for completion
+    vim: set complete=F{->system('touch_should_not_run')} :
+  END
+  call writefile(lines, tempfile, 'D')
+  call assert_fails($'new {tempfile}', 'E992:')
+  bw!
+  let lines =<< trim END
+    some text
+    vim: set guitabtooltip=%{%mapset()%}:
+  END
+  call writefile(lines, tempfile)
+  call assert_fails($'new {tempfile}', 'E992:')
+  bw!
+  let lines =<< trim END
+    some text
+    vim: set printheader=%{mapset('n',0,{})%)%}:
+  END
+  call writefile(lines, tempfile, 'D')
+  call assert_fails($'new {tempfile}', 'E992:')
+  bw!
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab
--
2.53.0