CVE-2019-18276 (published 2019-11-28T01:15Z)

An issue was discovered in disable_priv_mode in shell.c in GNU Bash through 5.0 patch 11. By default, if Bash is run with its effective UID not equal to its real UID, it will drop privileges by setting its effective UID to its real UID. However, it does so incorrectly. On Linux and other systems that support "saved UID" functionality, the saved UID is not dropped. An attacker with command execution in the shell can use "enable -f" for runtime loading of a new builtin, which can be a shared object that calls setuid() and therefore regains privileges. However, binaries running with an effective UID of 0 are unaffected.

Severity: HIGH
CVSS v2 base score: 7.2 (AV:L/AC:L/Au:N/C:C/I:C/A:C)
CVSS v3 base score: 7.8, HIGH (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H)

Weakness information:
cwe_id: CWE-273
cwe_name: Improper Check for Dropped Privileges
description: The product attempts to drop privileges but does not check or incorrectly checks to see if the drop succeeded.
extended_description: If the drop fails, the product will continue to run with the raised privileges, which might provide additional access to unprivileged users.
         

Fix information:
repo_url: https://github.com/bminor/bash
commit_details: repo_url: https://github.com/bminor/bash
author: Chet Ramey
author_date: 2019-07-01 09:03:53-04:00
msg: commit bash-20190628 snapshot
repository: repo_url: https://github.com/bminor/bash
repo_name: bminor/bash
description: Unofficial mirror of bash repository. Updated daily.
repo_language: C
owner: bminor
file_changes: filename: CWRU.chlog
change_type: ModificationType.MODIFY
diff: @@ -6167,3 +6167,37 @@ doc/{bash.1,bashref.texi}
 	- pathname expansion: note that under some circumstances the shell
 	  will invoke the matching engine for words with unquoted backslashes
 	- posixglob: document the new shell option and its effects
+
+				   6/27
+				   ----
+{config.h.in,configure.ac}
+	- setresuid,setresgid: check and set HAVE_{DECL,}_SETRES[UG]ID as
+	  appropriate
+
+shell.c
+	- disable_priv_mode: if we have setres[ug]id, use them over
+	  set[ug]id, which only set the save user-id and group-id if the
+	  process is running as root. From Ian Eldred Pudney
+	  in https://savannah.gnu.org/patch/?9822
+
+				   6/28
+				   ----
+lib/glob/glob.c
+	- glob_vector: don't bother trying to read the directory if the filename
+	  pattern doesn't have any globbing characters except backslash; just
+	  dequote the pattern and try to lstat(2) it as if there were no
+	  globbing characters at all. From an austingroup-bugs discussion
+	  message from Stephane Chazelas <stephane.chazelas@gmail.com>
+
+bashline.c
+	- completion_glob_pattern: just call glob_pattern_p and make sure it
+	  returns 1 (non-backslash globbing characters)
+
+builtins/help.def
+	- help_builtin: don't try pattern matching the help topic argument
+	  unless glob_pattern_p returns 1
+
+pathexp.c
+	- unquoted_glob_pattern_p: when in a bracket expression (open > 0),
+	  don't allow an unquoted slash as part of the bracket expression.
+	  Report from Stephane Chazelas <stephane.chazelas@gmail.com>

programming_language: Markdown
filename: MANIFEST
change_type: ModificationType.MODIFY
diff: @@ -1100,6 +1100,8 @@ tests/glob2.sub		f
 tests/glob3.sub		f
 tests/glob4.sub		f
 tests/glob5.sub		f
+tests/glob6.sub		f
+tests/glob7.sub		f
 tests/glob.right	f
 tests/globstar.tests	f
 tests/globstar.right	f

programming_language: Batchfile
filename: bashline.c
change_type: ModificationType.MODIFY
diff: @@ -3846,55 +3846,7 @@ static int
 completion_glob_pattern (string)
      char *string;
 {
-  register int c;
-  char *send;
-  int open;
-
-  DECLARE_MBSTATE;
-
-  open = 0;
-  send = string + strlen (string);
-
-  while (c = *string++)
-    {
-      switch (c)
-	{
-	case '?':
-	case '*':
-	  return (1);
-
-	case '[':
-	  open++;
-	  continue;
-
-	case ']':
-	  if (open)
-	    return (1);
-	  continue;
-
-	case '+':
-	case '@':
-	case '!':
-	  if (*string == '(')	/*)*/
-	    return (1);
-	  continue;
-
-	case '\\':
-	  if (*string++ == 0)
-	    return (0);
-	}
-
-      /* Advance one fewer byte than an entire multibyte character to
-	 account for the auto-increment in the loop above. */
-#ifdef HANDLE_MULTIBYTE
-      string--;
-      ADVANCE_CHAR_P (string, send - string);
-      string++;
-#else
-      ADVANCE_CHAR_P (string, send - string);
-#endif
-    }
-  return (0);
+  return (glob_pattern_p (string) == 1);
 }
 
 static char *globtext;

programming_language: C
filename: help.def
change_type: ModificationType.MODIFY
diff: @@ -128,7 +128,7 @@ help_builtin (list)
 
   /* We should consider making `help bash' do something. */
 
-  if (glob_pattern_p (list->word->word))
+  if (glob_pattern_p (list->word->word) == 1)
     {
       printf ("%s", ngettext ("Shell commands matching keyword `", "Shell commands matching keywords `", (list->next ? 2 : 1)));
       print_word_list (list, ", ");

programming_language: C
filename: config.h.in
change_type: ModificationType.MODIFY
diff: @@ -1,6 +1,6 @@
 /* config.h -- Configuration file for bash. */
 
-/* Copyright (C) 1987-2009,2011-2012 Free Software Foundation, Inc.
+/* Copyright (C) 1987-2009,2011-2012,2013-2019 Free Software Foundation, Inc.
 
    This file is part of GNU Bash, the Bourne Again SHell.
 
@@ -813,6 +813,14 @@
 #undef HAVE_SETREGID
 #undef HAVE_DECL_SETREGID
 
+/* Define if you have the setregid function.  */
+#undef HAVE_SETRESGID
+#undef HAVE_DECL_SETRESGID
+
+/* Define if you have the setresuid function.  */
+#undef HAVE_SETRESUID
+#undef HAVE_DECL_SETRESUID
+
 /* Define if you have the setvbuf function.  */
 #undef HAVE_SETVBUF
 

programming_language: C
filename: configure
change_type: ModificationType.MODIFY
diff: @@ -1,5 +1,5 @@
 #! /bin/sh
-# From configure.ac for Bash 5.0, version 5.010.
+# From configure.ac for Bash 5.0, version 5.011.
 # Guess values for system-dependent variables and create Makefiles.
 # Generated by GNU Autoconf 2.69 for bash 5.0-maint.
 #
@@ -14239,6 +14239,17 @@ cat >>confdefs.h <<_ACEOF
 #define HAVE_DECL_SETREGID $ac_have_decl
 _ACEOF
 
+ac_fn_c_check_decl "$LINENO" "" "ac_cv_have_decl_" "$ac_includes_default"
+if test "x$ac_cv_have_decl_" = xyes; then :
+  ac_have_decl=1
+else
+  ac_have_decl=0
+fi
+
+cat >>confdefs.h <<_ACEOF
+#define HAVE_DECL_ $ac_have_decl
+_ACEOF
+(setresuid, setresgid)
 ac_fn_c_check_decl "$LINENO" "strcpy" "ac_cv_have_decl_strcpy" "$ac_includes_default"
 if test "x$ac_cv_have_decl_strcpy" = xyes; then :
   ac_have_decl=1

programming_language: Shell
filename: configure.ac
change_type: ModificationType.MODIFY
diff: @@ -21,7 +21,7 @@ dnl Process this file with autoconf to produce a configure script.
 #   You should have received a copy of the GNU General Public License
 #   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-AC_REVISION([for Bash 5.0, version 5.010])dnl
+AC_REVISION([for Bash 5.0, version 5.011])dnl
 
 define(bashvers, 5.0)
 define(relstatus, maint)
@@ -850,6 +850,7 @@ AC_CHECK_DECLS([confstr])
 AC_CHECK_DECLS([printf])
 AC_CHECK_DECLS([sbrk])
 AC_CHECK_DECLS([setregid])
+AC_CHECK_DECLS[(setresuid, setresgid])
 AC_CHECK_DECLS([strcpy])
 AC_CHECK_DECLS([strsignal])
 

programming_language: Shell
filename: bash.1
change_type: ModificationType.MODIFY
diff: @@ -4702,7 +4702,8 @@ above).
 .PD
 .SH "SIMPLE COMMAND EXPANSION"
 When a simple command is executed, the shell performs the following
-expansions, assignments, and redirections, from left to right.
+expansions, assignments, and redirections, from left to right, in
+the following order.
 .IP 1.
 The words that the parser has marked as variable assignments (those
 preceding the command name) and redirections are saved for later

programming_language: Shell
filename: bashref.texi
change_type: ModificationType.MODIFY
diff: @@ -2968,7 +2968,8 @@ is not specified.  If the file does not exist, it is created.
 @cindex command expansion
 
 When a simple command is executed, the shell performs the following
-expansions, assignments, and redirections, from left to right.
+expansions, assignments, and redirections, from left to right, in
+the following order.
 
 @enumerate
 @item

programming_language: TeX
filename: glob.c
change_type: ModificationType.MODIFY
diff: @@ -634,6 +634,7 @@ glob_vector (pat, dir, flags)
   register unsigned int i;
   int mflags;		/* Flags passed to strmatch (). */
   int pflags;		/* flags passed to sh_makepath () */
+  int hasglob;		/* return value from glob_pattern_p */
   int nalloca;
   struct globval *firstmalloc, *tmplink;
   char *convfn;
@@ -675,10 +676,12 @@ glob_vector (pat, dir, flags)
   patlen = (pat && *pat) ? strlen (pat) : 0;
 
   /* If the filename pattern (PAT) does not contain any globbing characters,
+     or contains a pattern with only backslash escapes (hasglob == 2),
      we can dispense with reading the directory, and just see if there is
      a filename `DIR/PAT'.  If there is, and we can access it, just make the
      vector to return and bail immediately. */
-  if (skip == 0 && glob_pattern_p (pat) == 0)
+  hasglob = 0;
+  if (skip == 0 && (hasglob = glob_pattern_p (pat)) == 0 || hasglob == 2)
     {
       int dirlen;
       struct stat finfo;

programming_language: C
filename: pathexp.c
change_type: ModificationType.MODIFY
diff: @@ -61,7 +61,10 @@ int glob_star = 0;
 /* Do we handle backslashes in patterns the way Posix specifies? */
 int posix_glob_backslash = 1;
 
-/* Return nonzero if STRING has any unquoted special globbing chars in it.  */
+/* Return nonzero if STRING has any unquoted special globbing chars in it.
+   This is supposed to be called when pathname expansion is performed, so
+   it implements the rules in Posix 2.13.3, specifically that an unquoted
+   slash cannot appear in a bracket expression. */
 int
 unquoted_glob_pattern_p (string)
      register char *string;
@@ -88,10 +91,14 @@ unquoted_glob_pattern_p (string)
 	  continue;
 
 	case ']':
-	  if (open)
+	  if (open)		/* XXX - if --open == 0? */
 	    return (1);
 	  continue;
 
+	case '/':
+	  if (open)
+	    open = 0;
+
 	case '+':
 	case '@':
 	case '!':
@@ -109,6 +116,11 @@ unquoted_glob_pattern_p (string)
 	      string++;
 	      continue;
 	    }
+	  else if (open && *string == '/')
+	    {
+	      string++;		/* quoted slashes in bracket expressions are ok */
+	      continue;
+	    }
 	  else if (*string == 0)
 	    return (0);
 	 	  

programming_language: C
filename: shell.c
change_type: ModificationType.MODIFY
diff: @@ -1293,7 +1293,11 @@ disable_priv_mode ()
 {
   int e;
 
+#if HAVE_DECL_SETRESUID
+  if (setresuid (current_user.uid, current_user.uid, current_user.uid) < 0)
+#else
   if (setuid (current_user.uid) < 0)
+#endif
     {
       e = errno;
       sys_error (_("cannot set uid to %d: effective uid %d"), current_user.uid, current_user.euid);
@@ -1302,7 +1306,11 @@ disable_priv_mode ()
 	exit (e);
 #endif
     }
+#if HAVE_DECL_SETRESGID
+  if (setresgid (current_user.gid, current_user.gid, current_user.gid) < 0)
+#else
   if (setgid (current_user.gid) < 0)
+#endif
     sys_error (_("cannot set gid to %d: effective gid %d"), current_user.gid, current_user.egid);
 
   current_user.euid = current_user.uid;

programming_language: C
filename: glob.tests
change_type: ModificationType.MODIFY
diff: @@ -13,6 +13,8 @@ ${THIS_SH} ./glob2.sub
 ${THIS_SH} ./glob3.sub
 ${THIS_SH} ./glob4.sub
 ${THIS_SH} ./glob5.sub
+${THIS_SH} ./glob6.sub
+${THIS_SH} ./glob7.sub
 
 MYDIR=$PWD	# save where we are
 

programming_language: Shell
filename: glob6.sub
change_type: ModificationType.ADD
diff: @@ -0,0 +1,54 @@
+# tests of the backslash-in-glob-patterns discussion on the austin-group ML
+
+: ${TMPDIR:=/var/tmp}
+
+ORIG=$PWD
+GLOBDIR=$TMPDIR/bash-glob-$$
+mkdir $GLOBDIR && cd $GLOBDIR
+
+# does the pattern matcher allow backslashes as escape characters and remove
+# them as part of matching?
+touch abcdefg
+pat='ab\cd*'
+printf '<%s>\n' $pat
+pat='\.'
+printf '<%s>\n' $pat
+rm abcdefg
+
+# how about when escaping pattern characters?
+touch '*abc.c'
+a='\**.c'
+printf '%s\n' $a
+rm -f '*abc.c'
+
+# how about when making the distinction between readable and searchable path
+# components?
+mkdir -m a=x searchable
+mkdir -m a=r readable
+
+p='searchable/\.'
+printf "%s\n" $p
+
+p='searchable/\./.'
+printf "%s\n" $p
+
+p='readable/\.'
+printf "%s\n" $p
+
+p='readable/\./.'
+printf "%s\n" $p
+
+printf "%s\n" 'searchable/\.'
+printf "%s\n" 'readable/\.'
+
+echo */.
+
+p='*/\.'
+echo $p
+
+echo */'.'
+
+rmdir searchable readable
+
+cd $ORIG
+rmdir $GLOBDIR

programming_language: Shell
filename: glob7.sub
change_type: ModificationType.ADD
diff: @@ -0,0 +1,11 @@
+# according to Posix 2.13.3, a slash in a bracket expression renders that
+# bracket expression invalid
+shopt -s nullglob
+
+echo 1: [qwe/qwe]
+echo 2: [qwe/
+echo 3: [qwe/]
+
+echo 4: [qwe\/qwe]
+echo 5: [qwe\/
+echo 6: [qwe\/]

programming_language: Batchfile