From: Markus Koschany <apo@debian.org>
Date: Wed, 26 Oct 2022 23:24:00 +0200
Subject: CVE-2022-0413

Origin: https://github.com/vim/vim/commit/37f47958b8a2a44abc60614271d9537e7f14e51a
---
 src/ex_cmds.c                   | 19 +++++++++++++++----
 src/testdir/test_substitute.vim | 17 +++++++++++++++++
 2 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/src/ex_cmds.c b/src/ex_cmds.c
index b18f58c..5ad8913 100644
--- a/src/ex_cmds.c
+++ b/src/ex_cmds.c
@@ -4857,6 +4857,7 @@ do_sub(exarg_T *eap)
     int		save_do_all;		/* remember user specified 'g' flag */
     int		save_do_ask;		/* remember user specified 'c' flag */
     char_u	*pat = NULL, *sub = NULL;	/* init for GCC */
+    char_u	*sub_copy = NULL;
     int		delimiter;
     int		sublen;
     int		got_quit = FALSE;
@@ -5152,11 +5153,20 @@ do_sub(exarg_T *eap)
     sub_firstline = NULL;
 
     /*
-     * ~ in the substitute pattern is replaced with the old pattern.
-     * We do it here once to avoid it to be replaced over and over again.
-     * But don't do it when it starts with "\=", then it's an expression.
+     * If the substitute pattern starts with "\=" then it's an expression.
+     * Make a copy, a recursive function may free it.
+     * Otherwise, '~' in the substitute pattern is replaced with the old
+     * pattern.  We do it here once to avoid it to be replaced over and over
+     * again.
      */
-    if (!(sub[0] == '\\' && sub[1] == '='))
+    if (sub[0] == '\\' && sub[1] == '=')
+    {
+	sub = vim_strsave(sub);
+	if (sub == NULL)
+	    return;
+	sub_copy = sub;
+    }
+    else
 	sub = regtilde(sub, p_magic);
 
     /*
@@ -5925,6 +5935,7 @@ outofmem:
 #endif
 
     vim_regfree(regmatch.regprog);
+    vim_free(sub_copy);
 
     /* Restore the flag values, they can be used for ":&&". */
     subflags.do_all = save_do_all;
diff --git a/src/testdir/test_substitute.vim b/src/testdir/test_substitute.vim
index d84daa7..c1e8f30 100644
--- a/src/testdir/test_substitute.vim
+++ b/src/testdir/test_substitute.vim
@@ -500,3 +500,20 @@ func Test_sub_cmd_8()
   enew!
   set titlestring&
 endfunc
+
+" This was using "old_sub" after it was freed.
+func Test_using_old_sub()
+  set compatible maxfuncdepth=10
+  new
+  call setline(1, 'some text.')
+  func Repl()
+    ~
+    s/
+  endfunc
+  silent!  s/\%')/\=Repl()
+
+  delfunc Repl
+  bwipe!
+  set nocompatible
+endfunc
+